Endangered and Threatened Wildlife and Plants; Withdrawal of Proposed Rule To List the Flat-Tailed Horned Lizard as Threatened

DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R8-ES-2010-0008; MO 92210-0-0008]

RIN 1018-AX07

Endangered and Threatened Wildlife and Plants; Withdrawal of Proposed Rule To List the Flat-Tailed Horned Lizard as Threatened

AGENCY:

Fish and Wildlife Service, Interior.

ACTION:

Proposed rule; withdrawal.

SUMMARY:

We, the U.S. Fish and Wildlife Service (Service), determine that the listing of the flat-tailed horned lizard (

Phrynosoma mcallii

) as a threatened species under the Endangered Species Act of 1973, as amended (Act), is not warranted, and we therefore withdraw our November 29, 1993, proposed rule to list it under the Act. We made this determination in this withdrawal because threats to the species as identified in the 1993 proposed rule are not as significant as earlier believed, and available data do not indicate that the threats to the species and its habitat, as analyzed under the five listing factors described in section 4(a)(1) of the Act, are likely to endanger the species in the foreseeable future throughout all or a significant portion of its range.

DATES:

The November 29, 1993 (58 FR 62624), proposal to list the flat-tailed horned lizard as a threatened species is withdrawn as of March 15, 2011.

ADDRESSES:

This withdrawal of the proposed rule is available on the Internet at

http://www.regulations.gov.

Comments and materials received, as well as supporting documentation for this rulemaking is available for public inspection, by appointment, during normal business hours at the U.S. Fish and Wildlife Service, Carlsbad Fish and Wildlife Office, 6010 Hidden Valley Road, Suite 101, Carlsbad, CA 92011; telephone 760-431-9440; facsimile 760-431-9624.

FOR FURTHER INFORMATION CONTACT:

Jim Bartel, Field Supervisor, Carlsbad Fish and Wildlife Office (

see

ADDRESSES

section). If you use a telecommunications device for the deaf (TDD), call the Federal Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION:

Background

The flat-tailed horned lizard (

Phrynosoma mcallii

) is a small, spiny lizard found in the Sonoran Desert of the southwestern United States and northwestern Mexico. All of the species of lizards in the genus

Phrynosoma

—the horned lizards—have dorso-ventrally flattened, “pancake-like” bodies; spiny scales; head spines or “horns”; cryptic coloration; and certain similar behavioral traits (Sherbrooke 2003, pp. 4-17; Stebbins 2003, p. 299; Leaché and McGuire 2006, p. 629).

Among horned lizard species, the flat-tailed horned lizard has particularly long and sharp horns (Funk 1981, p. 281.1; Sherbrooke 2003, p. 40; Young

et al.

2004a, p. 65). Other characteristics that help distinguish flat-tailed horned lizards from other members of the genus include a dark line down the middle of the back (vertebral stripe), lack of external ear openings, two rows of fringe scales, an unspotted vent, and—as indicated by its common name—a long, broad, flattened tail (Funk 1981, p. 281.1; Sherbrooke 2003, p. 40). The flat-tailed horned lizard is average in size when compared to other horned lizard species. Flat-tailed horned lizards become adults when about 60 to 64 millimeters (mm) (2.4 to 2.5 inches (in)) long, not including the tail (snout-to-vent length), and may grow to be about 87 mm (3.4 in) long (Young and Young 2000, p. 34; Rorabaugh and Young 2009, p. 182). The dorsal coloration of flat-tailed horned lizards varies and closely matches the colors of the desert soils on which they live, ranging from pale gray to light rust-brown, while their ventral coloration is white or cream-colored (Funk 1981, p. 281.1; Flat-tailed Horned Lizard Interagency Coordinating Committee [FTHLICC] 2003, p. 1; Stebbins 2003, p. 304). First described by Hallowell in 1852, no subspecies have been described or are recognized for the flat-tailed horned lizard (Crother

et al.

2008, p. 35).

The flat-tailed horned lizard occurs within the range of the desert horned lizard (

Phrynosoma platyrhinos

). Additionally, Goode's horned lizard (

P.

[

platyrhinos

]

goodie

), which Klauber (1935, p. 179) considered to be a subspecies of the desert horned lizard (Klauber 1935, p. 179), also occurs within the range of the flat-tailed horned lizard in the portion southeast of the confluence of the Gila and Colorado Rivers (Mulcahy

et al.

2006, p. 1823). Recent genetic analyses support Goode's horned lizard as a differentiable evolutionary species (Mulcahy

et al.

2006, pp. 1807-1826). Hybrids between flat-tailed and Goode's horned lizards, exhibiting a mix of morphological and genetic characters, have been observed southeast of Yuma, Arizona (Mulcahy

et al.

2006, p. 1810), while apparent hybrids between flat-tailed and desert horned lizards have been observed in the vicinity of Ocotillo, California (Stebbins 2003, p. 302). Additionally, the regal horned lizard (

P. solare

) also occurs in northwestern Sonora, Mexico (Rorabaugh 2008, p. 39); we are not aware of hybridization with this species.

Life History

Flat-tailed horned lizards are oviparous (egg-laying), are early maturing, and may produce multiple clutches within a breeding season (Howard 1974, p. 111; Turner and Medica 1982, p. 819), which, when it occurs, results in two groups of individuals in a single year that are all generally the same age (that is, two cohorts). However, some authors question whether the observed two cohorts is the result of individual females producing two clutches in a year or whether different groups of females lay eggs at different times (Muth and Fisher 1992, p. 46; Young and Young 2000, p. 11). Flat-tailed horned lizards produce relatively small clutches of eggs (mean clutch size = 4.7; range = 3 to 7) (Howard 1974, p. 111) compared to most other horned lizards (Sherbrook 2003, p. 139). The first cohort hatches in July to August (Muth and Fisher 1992, p. 19; Young and Young 2000, p. 13), and when it occurs, the second cohort may be produced in September (Howard 1974, p. 111; Muth and Fisher 1992, p. 19). Hatchlings from the first cohort may reach sexual maturity after their first winter season, whereas individuals that hatch later may require an additional growing season to mature (Howard 1974, p. 111). Flat-tailed horned lizards typically live for 4 years, or rarely even 6 years, in the wild (FTHLICC 2003a, p. 10).

A

home range

is the area in which an animal (as an individual) typically lives. Flat-tailed horned lizards can have relatively large home ranges compared to other species of lizards of similar size (FTHLICC 2003a, p. 9). Muth and Fisher (1992, p. 34) found the mean home range size was 2.7 hectares (ha) (6.7 acres (ac)) on the West Mesa, California. In the Yuma Desert of Arizona, Young and Young (2000, p. 54) found mean home ranges for males differed between drought and wet years, while those of females did not. The mean home range size for males was 2.5 ha (6.2 ac) during a dry year versus 10.3 ha (25.5 ac) during a wet year. Female mean home ranges were smaller at 1.3 ha (3.2 ac) and 1.9 ha (4.7 ac) in dry and wet years, respectively (Young and Young 2000, p. 54). Young and Young (2000, p. 55) noted a wide variation in movement

patterns, with a few home ranges estimated at greater than 34.4 ha (85 ac).

Flat-tailed horned lizards are not known to drink standing water (FTHLICC 2003a, p. 8), but they apparently do rain-harvest (Grant 2005, pp. 66-67), which is a behavior that some horned lizard species use to channel precipitation or condensation collected on the lizard's body to its mouth for consumption (Sherbrook 2003, p. 104). Thus, nearly all of the water consumed by flat-tailed horned lizards is from the food they eat (preformed water) (FTHLICC 2003a, p. 8; Grant 2005, pp. 66-67). Most horned lizard species, including the flat-tailed horned lizard, are ant-foraging specialists (Pianka and Parker 1975, pp. 141-162; Sherbrooke and Schwenk 2008, pp. 447-459). More than 95 percent of the diet of flat-tailed horned lizards is composed of ants, with species of harvester ants (genera

Messor

and

Pogonomyrmex

) predominating in most areas of the lizard's range, but species of

Dorymyrmex, Pheidole,

and

Myrmecocystus

are also consumed (Pianka and Parker 1975, p. 148; Turner and Medica 1982, p. 820; Young and Young 2000, p. 38; FTHLICC 2003a, p. 8).

Flat-tailed horned lizards, typical of reptiles, obtain their body heat from the surrounding environment (ectothermic) (Mayhew 1965, p. 104; Sherbrooke 2003, pp. 75-81). To gain body heat, they bask in the sun, often on rocks or other substrates that are warmed by insolation. During the heat of the day, to escape extreme surface temperatures, flat-tailed horned lizards may bury themselves just below the surface (Norris 1949, pp. 178-179) or retreat to a burrow made by other organisms (Young and Young 2000, p. 12). Adult flat-tailed horned lizards are reported to be obligatory hibernators (

i.e.,

an organism that must enter a dormant period regardless of environmental conditions) (Mayhew 1965, p. 103). Hibernation may begin as early as October and end as late as March (Muth and Fisher 1992, p. 33), although individuals have been noted on the surface during January and February (FTHLICC 2003a, p. 9). Hibernation burrows appear to be self-constructed (as opposed to using burrows constructed by other animals) and are typically within 10 centimeters (cm) (3.9 in) of the surface (Muth and Fisher 1992, p. 33). Mayhew (1965, p. 115) found that the majority of lizards hibernated within 5 cm (2 in) of the surface, with one as deep as 20 cm (8 in) below the surface.

Flat-tailed horned lizards generally lie close to the ground and remain motionless when approached (Wone and Beauchamp 1995, p. 132); however, they may occasionally bury themselves in loose sand if it is available (Norris 1949, p. 176), and even more rarely, flee (Young and Young 2000, p. 12). Their propensity to remain motionless and bury in the sand, along with their cryptic coloration and flattened body, make them difficult to detect visually, which serves as a way to evade predators but also makes them difficult for surveyors to find in the field (FTHLICC 2003a, pp. 9, 65; Grant and Doherty 2007, p. 1050) (see also “

Population Dynamics

” section, below).

Additional life-history information is available in the Flat-tailed Horned Lizard Rangewide Management Strategy (FTHLICC 2003a, pp. 6-11).

Setting and Habitat

The flat-tailed horned lizard is endemic (restricted) to the Salton Trough and the region north of the Gulf of California in northwest Sonora, Mexico, both of which lie within the Lower Colorado Subdivision of the Sonoran Desert (Shreve and Wiggins 1964, p. 6). The climatic conditions over the range of the flat-tailed horned lizard are characterized by hot summer temperatures, mild winter temperatures, and little rainfall. Winter rainfall predominates in the western portion of the species' range while summer rainfall predominates in the eastern portion of the species' range (Shreve and Wiggins 1964, pp. 17-20, 49, 50; Johnson and Spicer 1985, p. 14). Periods of drought are not uncommon (Shreve and Wiggins 1964, p. 18).

Although the region in northwest Sonora, Mexico, represents roughly half of the current range of the flat-tailed horned lizard, its distribution within the Salton Trough has been more dynamic. As discussed below, the geologic and land use changes in the Salton Trough have substantially shaped the status of the species today.

To better understand population trends of the flat-tailed horned lizard relative to the geologic setting and its current distribution within sandy habitat, we are providing a summary of the recent geologic history of the area in the following paragraphs (summarized from Parish 1914, pp. 85-114; Sykes 1914, pp. 13-20; Durham and Alison 1960, pp. 47-91; van de Kamp 1973, pp. 827-848; Waters 1983, pp. 373-387; Blount and Lancaster 1990, pp. 724-728; Blount

et al.

1990, pp. 15,463-15,482; Stokes

et al.

1997, pp. 63-75; Patten

et al.

2003, pp. 1-6; Li

et al.

2008, pp. 182-197).

The Salton Trough (Trough) is a low-elevation valley that represents the northwestward continuation of the Gulf of California. During the period starting at least several million years ago, as sea levels rose and fell, the Gulf of California filled the present-day Salton Trough, often extending the Gulf northward into the present-day San Gorgonio Pass, east of Cabazon, California. The Colorado River flowed into the Gulf at roughly the same geographical area as today, but with the Gulf extending to a more northerly point, the river flowed into the Gulf mid-way along its length.

The Colorado River, which originates in the Rocky Mountains and flows through the Grand Canyon, historically transported large quantities of fine-grained sediment. Where the river joined the Gulf, sediments were deposited forming a broad delta. These sediments continued to increase and created a barrier that divided the Gulf into a land-locked northern portion (the Trough) and a marine-linked southern portion (the Gulf). The northern portion, which remains below sea level but without a direct connection with the ocean, eventually dried out. However, the Colorado River continued to meander across its delta and seasonal flooding promoted avulsion (i.e., abandonment of an old river channel and the creation of a new one). Thus, the river would sometimes flow into the Gulf and sometimes into the Trough, the lowest point of which—referred to as the Salton Basin—is about minus 84 meters (m) elevation (277 feet (ft) below sea level).

Water from the meandering Colorado River periodically filled the Salton Basin to varying depths (and areal extent), depositing sediments in the process. The lake that periodically formed, especially in its recent but prehistoric incarnations, is referred to by most authors as Lake Cahuilla. Its maximum depth depended on elevation of the delta, which is now about 12 m elevation (39 ft above sea level). The Lake was full as recently as the early 1600s, but smaller, shallower manifestations were present at various times since then (including the modern Salton Sea, discussed below). When Lake Cahuilla was full, the Colorado River water flowed into the Basin from the southeast, marked today by the Alamo River and New River channels, and exited the Basin farther west along a southerly route, marked today by the Río Hardy channel, ultimately emptying into the Gulf of California. Floodwaters and sediments also periodically flowed into Laguna Salada, in northwestern Baja California, Mexico. Thus, even areas of the present-day Imperial, Mexicali, and San Luis Valleys that

were never or were less-frequently inundated by Lake Cahuilla, were regularly influenced by hydrologic forces associated with the Colorado River. Despite being in the middle of one of the driest deserts in North America, some of these areas were, at least periodically, part of an intricate water distribution system of channels, sloughs, and lagoons.

Water also flowed into the Trough from surrounding highlands, bringing locally derived sediments with it. One notable inflow is marked by the present-day Whitewater River that flows into the Basin from the north. Water from the local sources would occasionally result in standing water in the Basin, but these sources could not compete with the sheer volume the Colorado River periodically provided.

After flowing into the Trough for a period of time, the Colorado River would eventually meander back and once again flow into the Gulf. Over time, Lake Cahuilla would then become dry and the transported sediments would become exposed, with local sediment sources predominating the north end of the Trough, and Colorado River-derived sediments predominating the south end of the Trough. During dry periods, the fine-grained sediments in the Trough would be transported and sorted by prevailing winds. Thus, much of the Trough outside of those areas that were regularly influenced by the flooding and meandering of the Colorado River was ultimately blanketed with soft, friable (crumbly) or arenaceous (sandy) soils. Similarly, sediments deposited in the Colorado River delta and along the northeast shore of the Gulf of California were transported by winds where they formed areas of soft, friable (crumbly) or arenaceous (sandy) soils, including the “sand sea” of the Gran Desierto de Altar.

As a result, typical flat-tailed horned lizard habitat today includes areas of these sandy flats as well as the associated valleys created by these geologic events. Turner

et al.

(1980, p. 14) stated the best habitats are generally low-relief areas with surface soils of packed, fine sand or low-relief areas of pavement (hardpan) overlain with loose, fine sand. However, the available scientific information indicates that flat-tailed horned lizards may occur in areas with soil substrates and plant associations that differ from these generalizations, as described below.

Flat-tailed horned lizards are also known to occur at the edges of vegetated sand dunes, on barren clay soils, and within sparse

Atriplex

spp. (saltbush) plant communities. Although Turner

et al.

(1980, p. 15) suspected that these recorded occurrences were actually individuals that had dispersed from more suitable habitats, Wone

et al.

(1991, p. 16) questioned this conclusion (see also Wone and Beauchamp 1995, p. 132; Beauchamp

et al.

1998, p. 213), suggesting instead that flat-tailed horned lizards regularly occupy at least some of these areas.

Within a creosote plant community in the West Mesa area, Muth and Fisher (1992, p. 61) found that flat-tailed horned lizards preferred sandy substrates with white bursage and

Psorothamnus emoryi

(Emory dalea), and avoided areas with creosote and

Tiquilia plicata

(fanleaf crinklemat). In Arizona, Rorabaugh

et al.

(1987, p.103) found flat-tailed horned lizard abundance correlated with

Pleuraphis rigida

(big galleta grass) and sandy substrates, but they suggested that the presence of sandy substrates was more important than grass.

Several researchers have investigated the relationship between density of perennial plants and flat-tailed horned lizard abundance. The observed relationships varied among studies. For example, Altman

et al.

(1980, p.

ii

) and Turner and Medica (1982, p. 815) found the relative abundance of flat-tailed horned lizards was significantly and positively correlated with perennial plant density in creosote-white bursage plant communities (that is, horned lizard abundance increased as perennial plant density increased). In contrast, Beauchamp

et al.

(1998, p. 210) found flat-tailed horned lizards to be present in higher densities in sparsely vegetated areas with large patches of concretions (i.e., a volume of sedimentary rock in which a mineral cement fills the spaces between the sediment grains), gravel, and silt, than in areas that were sandy or densely vegetated. Altman

et al.

(1980, p. 7) also reported finding flat-tailed horned lizards in desert pavement areas. Foley (2002, p. 54) found little correlation in substrate texture and distribution of flat-tailed horned lizards, when using three experimental treatments consisting of sandy, rocky and mixed substrates. However, Wright and Grant (2003, p. 3) found flat-tailed horned lizard abundance was positively correlated with percentage of sand cover. Thus, flat-tailed horned lizard habitat includes a variety of soils and other plant associations, but the habitat is best characterized as sandy flats and valleys in a creosote-white bursage plant association.

Plants and harvester ants are important components to flat-tailed horned lizard habitat because they comprise its primary food chain. Seeds make up the primary food of harvester ants (Johnson 2000, p. 92). The ants often collect seeds from annual plants, including some nonnative species (Rissing 1988, p. 362), but they also gather seeds from perennial plants (Gordon 1980, p. 72). Thus, a simplified food chain for the flat-tailed horned lizard may be described as follows: Plants produce seeds, harvester ants eat the seeds, and flat-tailed horned lizards eat harvester ants.

Range and Distribution

A species' range is the region over which it is distributed. The range of the flat-tailed horned lizard includes the Salton Trough and the region north of the Gulf of California. In general, this range includes portions of southeastern California (eastern San Diego County, central Riverside County, and southwestern Imperial County) and southwestern Arizona (southwestern Yuma County) in the United States, and northeastern Baja California and northwestern Sonora in Mexico (Turner and Medica 1982, p. 815) (Figure 1). Within its range, the flat-tailed horned lizard is limited to areas below an upper elevation. Although the species has been recorded as high as 520 m (1,706 ft) above sea level (Turner

et al.

1980, p. 13), flat-tailed horned lizards are more commonly found below about 230 m (about 750 ft) in elevation (FTHLICC 2003a, p. 3).

BILLING CODE 4310-55-P

EP15MR11.041

BILLING CODE 4310-55-C

Extensive manmade changes, chiefly for agriculture, have occurred over a large portion of the land within the Salton Trough. Below we present a summary of the history of agricultural development in the Salton Trough (summarized from Furnish and Ladman 1975, pp. 83-107; Woerner 1989, pp. 109-112; Imperial Irrigation District [IID] 2002, pp. 3.1-66 to 3.1-77; Patten

et al.

2003, pp. 1-6).

Near the start of the 20th century, a canal was built to import water to the Salton Trough from the Colorado River. The Salton Basin is below sea level and much of the rest of the Salton Trough is at a lower elevation than where the head of the canal was located. Thus, with the regionally abundant sunshine and river-sediment soils, the importation of water by a gravity-fed system allowed agriculture to proliferate. For example, by 1904 approximately 60,700 ha (150,000 ac) were in cultivation.

Unlike the current canal, the original canal was poorly designed because it had no headgate to regulate flows into the canal. Prior to extensive dams on the Colorado River, the river was prone to flooding. The high waters of one such flood during the winter of 1904-05 flowed into the canal. Soon, nearly the entire Colorado River flowed through the canal, releasing water into the Salton Basin. Part of the flow followed the two historical riverbeds (the Alamo River and the New River) that were deepened and widened by the torrent. Despite heroic efforts, the flow continued until 1907. The Salton Basin filled to a depth of about 22 m (72 ft) (at its deepest point) and covered about 121,400 ha (300,000 ac), thus creating the modern Salton Sea.

Although the “creation” of the Salton Sea is often times described as an accident, the inundation of the Salton Basin by water flowing from the Colorado River from 1905 to 1907 was merely the most recent of many such inundations over historical and prehistorical times (

see

“

Setting and Habitat”

section above). Even without the canal, the flood of 1905 may have naturally flowed into the Basin.

Since the formation of the modern Salton Sea, agricultural practices in the region have maintained the water levels of the Salton Sea. If too much irrigation water is allowed to evaporate in the fields, salt levels, which are high in Colorado River water, build up in the soil, making it inhospitable for crops. To prevent this hypersalinization of the soils, a surplus of water is used for irrigation. The excess water drains by gravity from the fields through a network of ditches into the Salton Sea. Even with the high evaporation rates in the desert climate, inflow rates of drainage water have been high enough to maintain, and, for a time, even increase, the surface water elevation of the Salton Sea.

Efforts to bring irrigation water to the region continued through the 1900s, and the system of irrigation canals was eventually improved and expanded. In addition to the Imperial Valley, the Coachella Canal was constructed to bring water to the southern Coachella Valley, allowing irrigated agriculture to develop north of the Salton Sea. Similar canal systems were built in Mexico, allowing agriculture to develop and expand in the Mexicali and San Luis Valleys. Because these systems were gravity fed, the distribution canals within the region were dictated by elevation, which in turn, determined where irrigated agricultural development occurred. Thus, the majority of agricultural development was confined within the outer-most (highest elevation) canals. Moreover, croplands (and associated urbanization and infrastructure) were contiguous in the Salton Trough region, with little to no intervening undeveloped natural areas. Additionally, smaller amounts of agricultural development using pumped groundwater have occurred on a smaller scale outside these areas.

The geographically confined agricultural growth in the region is currently limited by the amount of water available from the Colorado River, which is dependent on annual precipitation in the Upper and Lower Colorado River Basins. The amount of irrigation water that can be delivered to the Salton Trough from the Colorado River is limited by interstate and international agreements (Furnish and Ladman 1975, pp. 83-107). Water conservation and transfer agreements completed in 2003 with the San Diego County Water Authority, Imperial Irrigation District, Metropolitan Water District of Southern California, and Coachella Valley Water District has reduced the amount of water available in the Imperial Valley and some fields have been fallowed, resulting in a decrease in the amount of irrigated agriculture in this region (IID 2006, p. 1).

Aerial and satellite imagery (Carlsbad Fish and Wildlife Office geographic information system (GIS) files) illustrates the development of active cultivation and associated urbanization and infrastructure extending from the present-day delta of the Colorado River, with a longer fork extending north-northwest through the Mexicali and Imperial Valleys to the Coachella Valley (punctuated by the Salton Sea), and a smaller fork extending northeast through the eastern Mexicali Valley and the San Luis Valley (Lower Colorado River Valley) to Yuma. Although there are specimens of flat-tailed horned lizards collected historically from within the now-altered region (Funk 1981, p. 281.1; Johnson and Spicer 1985, pp. 14-24), areas of agricultural and urban development do not constitute habitat for the flat-tailed horned lizard, and this continuous swath of altered land use is no longer occupied by flat-tailed horned lizards.

The current distribution of the flat-tailed horned lizard is often described within four, geographically descriptive “populations.” We use the term population in this document to refer to a loosely bounded, regionally distributed collection of individuals of the same species. These four populations are defined as:

(1) The Coachella Valley Population, including those individuals northwest of the Salton Sea, California;

(2) The Western Population, including those individuals in the areas west of the Salton Sea and the Imperial Valley, California, and west of the Mexicali Valley, Baja California, Mexico;

(3) The Eastern Population, including those individuals in the areas east of the Salton Sea and the Imperial Valley but west of the Colorado River; and

(4) The Southeastern Population, including those individuals in the areas east of the Colorado River, extending from Yuma south into Mexico and east to the Gulf of California.

These current designations closely follow the description of populations discussed in our January 3, 2003, analysis (68 FR 331), although in that document we used the United States-Mexico border to further divide the populations (see Figure 1 above). Additionally, these populations roughly correspond to those used by Mulcahy

et al.

(2006, pp. 1807-1826) in their analysis of flat-tailed horned lizard genetic data (see below for details). At the end of the Background section, below, we summarize these four populations in greater detail. We also use these four population names to identify the geographical habitat they occupy.

Populations and Genetics

The separation of the four populations of flat-tailed horned lizards described above in the “

Range and Distribution”

section is supported by genetic data, to varying degrees. Analyses of mitochondrial DNA data (Mulcahy

et al.

2006, pp. 1807-1826; see also Mendelson

et al.

2004, pp. 1-42) and nuclear microsatellite data (Culver and

Dee 2008, pp. 1-14) revealed significant differences in the prevalence of certain alleles in flat-tailed horned lizard populations on either side of the Colorado River; that is, the Southeastern Population differs from the other three populations. These analyses also showed that more gene flow has occurred near the Colorado River delta, suggesting the shifting course of the river over time in this area posed less of a barrier than the more stable portions of the river channel farther north (Mulcahy

et al.

2006, p. 1822; Culver and Dee 2008, p. 11). Although Culver and Dee (2008, p. 10) noted genetic variation in some individuals across the Southeastern Population, they found that flat-tailed horned lizards in Arizona are “not genetically isolated from neighboring populations in Mexico.” Thus, the flat-tailed horned lizards east of the Colorado River (i.e., the Southeastern Population) may be considered one population that is significantly and genetically distinct from the populations west of the river (i.e., the Coachella Valley, Western, and Eastern Populations).

The three populations west of the Colorado River also showed varying levels of genetic differentiation. Mulcahy

et al.

(2006, p. 1821) noted the Eastern Population “was significantly differentiated from [the Western and Coachella Valley Populations], suggesting that there has not been substantial gene flow across the Imperial Valley since the drying of Lake Cahuilla.” However, the difference between the Coachella Valley and Western Populations was less pronounced. Although their difference was supported by the presence of haplotypes unique to the Coachella Valley Population (Mulcahy

et al.

2006, Table 1 on p. 1811, and p. 1817), the difference between the Western and Coachella Valley Populations was not statistically significant (the other populations had unique haplotypes, too). This lack of significant difference suggested to the authors that the Coachella Valley Population “had more recent gene flow” with the Western Population (Mulcahy

et al.

2006, p. 1821). Thus, genetic data readily support three of the four geographic populations described above, but the distinction between the Western and Coachella Valley Populations is weak or equivocal. This suggests that the Coachella Valley Population was not a separate population historically, but is one now because it was “created” by an artificial barrier resulting from past agricultural and urban development.

Management and Populations

Three notable management mechanisms are in place within the U.S. portion of the flat-tailed horned lizard range: the Interagency Conservation Agreement, which includes the Flat-tailed Horned Lizard Rangewide Management Strategy (Rangewide Management Strategy); the Coachella Valley Multiple Species Habitat Conservation Plan (Coachella Valley MSHCP); and the Lower Colorado River Multi-Species Conservation Plan (Lower Colorado MSCP). Implementation of the Interagency Conservation Agreement has recently positively affected and is anticipated to continue to positively affect the status of flat-tailed horned lizard populations in the United States and, to a lesser extent, in Mexico. The recently permitted Coachella Valley MSHCP is also worth noting because it is a regional habitat conservation plan (HCP) developed under section 10 of the Act that covers the flat-tailed horned lizard in the Coachella Valley, an area addressed at length in our previous withdrawals. Additionally, the Lower Colorado MSCP is also an HCP that addresses the flat-tailed horned lizard.

Interagency Conservation Agreement and Flat-tailed Horned Lizard Rangewide Management Strategy

In June of 1997, the Service, Bureau of Land Management (BLM), Bureau of Reclamation (BOR), U.S. Marine Corps, U.S. Navy, Arizona Game and Fish Department, California Department of Fish and Game (CDFG), and California Department of Parks and Recreation (CDPR) entered into an Interagency Conservation Agreement. All signatories agreed to:

(1) Further develop and implement the objectives, strategies, and tasks of the Flat-tailed Horned Lizard Rangewide Management Strategy [original, FTHLICC 1997, pp. 1-106; revised: FTHLICC 2003a, p. 104; see below];

(2) As needed for the conservation effort, and as available, provide program personnel with facilities, equipment, logistical support, and access to lands under their control;

(3) Participate regularly in Interagency Coordinating Committee and Management Oversight Group meetings to enhance communication and cooperation, and to help develop annual or other work plans and reports;

(4) Develop and distribute public information and educational materials on the conservation effort;

(5) Provide ongoing review of, and feedback on, the conservation effort;

(6) Cooperate in development of major media releases and media projects;

(7) Keep local governments, communities, the conservation community, citizens, and other interested and affected parties informed on the status of the conservation effort, and solicit their input on issues and actions of concern or interest to them;

(8) Whenever possible, develop voluntary opportunities and incentives for local communities and private landowners to participate in the conservation effort; and

(9) Assist in generating the funds necessary to implement the conservation effort.

The purpose of the Rangewide Management Strategy is to provide a framework for conserving sufficient habitat to maintain several viable populations of the flat-tailed horned lizard throughout the range of the species in the United States. The Rangewide Management Strategy was developed by an interagency working group over a 2-year period. Despite being a voluntary agreement, many of the measures to conserve flat-tailed horned lizards are formally incorporated into planning documents of participating agencies, such as the Bureau of Land Management's California Desert Conservation Area Plan.

As part of the Interagency Conservation Agreement, agencies delineated specific areas under their jurisdiction as Management Areas. As of 2009, approximately 185,653 ha (458,759 ac) of the flat-tailed horned lizard habitat managed by signatories of the Interagency Conservation Agreement exists within five Management Areas (see Table 1 below) (FTHLICC 2009, p. 10). These Management Areas include the Borrego Badlands, West Mesa, and Yuha Desert (also referred to as the Yuha Basin) in the Western Population, the East Mesa in the Eastern Population, and the Yuma Desert in the Southeastern Population (Figure 2). Additionally, the Ocotillo Wells State Vehicular Recreation Area (SVRA) was designated as a research area.

EP15MR11.042

The five Management Areas were designed to include large areas of public land in the United States where flat-tailed horned lizards have been found, and to include most flat-tailed horned lizard habitat identified by the FTHLICC (1997, p. 35) as “key” areas for survival as determined in previous studies (Turner

et al.

1980, pp. 1-47; Turner and Medica 1982, pp. 815-823; Rorabaugh

et al.

1987, pp. 103-109). Management Areas were proposed based on standard principles of preserve design, utilizing the best information available at the time (FTHLICC 2003a, p. 47).

The Management Areas were delineated to include areas as large as possible, while avoiding extensive, existing and predicted management conflicts (such as off-highway vehicle (OHV) open areas). The Management Areas are meant to be the core areas for maintaining self-sustaining populations of flat-tailed horned lizards in the United States (FTHLICC 2003a, p. 24). The Management Areas constitute roughly 42 percent of the U.S. current distribution. Although the majority of lands within each Management Area are State or federally owned, some private inholdings occur within Management Area boundaries.

The 2003 Rangewide Management Strategy includes measures to avoid, minimize, and compensate impacts to the flat-tailed horned lizard and its habitat from construction projects and other development activities permitted by signatory agencies. As described in detail in the Rangewide Management Strategy (FTHLICC 2003a, pp. 58-60), the avoidance and minimization measures include (in part) avoidance of flat-tailed horned lizard Management Areas and the Research Area, project oversight and compliance measures, minimized project footprint, use of existing roads rather than creating new roads, use of barrier fencing, and project-specific habitat restoration. The Rangewide Management Strategy outlines avoidance, minimization, and mitigation measures intended to limit the impacts from permitted projects within the Management Areas to a maximum of 1 percent of the total area of each Management Area (FTHLICC 2003a, pp. 24-43). Additionally, the Rangewide Management Strategy (FTHLICC 2003a, pp. 60-62) describes compensation measures for projects within and outside the Management Areas where residual effects would occur after all reasonable on-site mitigation has been applied. The goal of compensation under the Rangewide Management Strategy is to “prevent the net loss of [flat-tailed horned lizard] habitat and make the net effect of a project neutral or positive to [flat-tailed horned lizards] by maintaining a habitat [baseline]” (FTHLICC 2003a, p. 61). Compensation funds may be used “to acquire, protect, or restore [flat-tailed horned lizard] habitat both within and contiguous with [Management Areas]” (FTHLICC 2003a, p. 60). Compensation ratios range from one-to-one to six-to-one (meaning, in latter ratio for instance, that six acres-worth of compensation will be required for every one acre of impact), depending on the location and nature of the impacts (FTHLICC 2003a, p. 61). Funds obtained through compensation associated with implementation of the Rangewide Management Strategy are being used to consolidate land ownership within the Management Areas or to enhance flat-tailed horned lizard habitat (FTHLICC 2003a, p. 25; FTHLICC 2010, p. 8). The original and current acreages of each Management Area are listed in Table 1.

Table 1—Area (hectares and acres) of Flat-tailed Horned Lizard Management Areas Owned by Signatories to the Interagency Conservation Agreement Implementing the Flat-tailed Horned Lizard Rangewide Management Strategy and Area Owned by Non-signatories (Predominantly Private) in 1997 and Through 2009, Plus Area and Percentage of Project-related Impacts Permitted by Signatories Within Each Management Area (Sources: FTHLICC 1997, p. 74; FTHLICC 2003a, p. 48; FTHLICC 2009, p. 10; FTHLICC 2010, p. 8)

Management area

Area of

signatory lands in 1997

Area of non-signatory lands in 1997

Area of non-signatory lands added to

signatory lands since 1997

Total area of

signatory lands in 2009

Total area of

management area

Total area

permitted for

impact as of 2009

Percent of total area of

management area permitted for impact as of 2009 (percent)

Borrego Badlands

14,771 ha (36,500 ac)

2,388 ha (5,900 ac)

592 ha *(1,464 ac)

15,363 ha (37,964 ac)

17,159 ha (42,400 ac)

0 ha (0 ac)

0.0

West Mesa

46,256 ha (114,300 ac)

8,822 ha (21,800 ac)

2,624 ha (6,483 ac)

48,880 ha (120,785 ac)

55,078 ha (136,100 ac)

86.77 ha (214.42 ac)

0.16

Yuha Desert

23,148 ha (57,200 ac)

1,214 ha (3,000 ac)

0 ha (0 ac)

23,148 ha (57,200 ac)

24,362 ha (60,200 ac)

35.90 ha (88.70 ac)

0.15

East Mesa

43,868 ha (108,400 ac)

2,792 ha (6,900 ac)

1,380 ha (3,410 ac)

45,248 ha (111,810 ac)

46,660 ha (115,300 ac)

38.40 ha (94.90 ac)

0.08

Yuma Desert

46,741 ha (115,500 ac)

6,273 ha (15,500 ac)

6,273 ha (15,500 ac)

53,014 ha (131,000 ac)

53,014 ha (131,000 ac)

10.50 ha (25.95 ac)

0.02

Total

174,784 ha (431,900 ac)

21,489 ha (53,100 ac)

10,869 ha (26,857 ac)

185,653 ha (458,759 ac)

196,273 ha (485,000 ac)

171.57 ha (423.97 ac)

0.09

* Includes 350 ha (864 ac) owned by the Anza-Borrego Foundation.

Representatives from the agencies participating on the Rangewide Management Strategy (also known as the Interagency Coordinating Committee) meet several times a year to coordinate and implement management actions (FTHLICC 2003a, pp. 1-104). The Interagency Coordinating Committee regularly documents progress made to conserve the flat-tailed horned lizard collectively or by participating agencies (FTHLICC 1998, pp. 1-11; FTHLICC 1999, pp. 1-13; FTHLICC 2001, pp. 1-24; FTHLICC 2003b, pp. 1-32; FTHLICC 2004, pp. 1-33; FTHLICC 2005, pp. 1-37; FTHLICC 2006, pp. 1-34; FTHLICC 2007, pp. 1-33; FTHLICC 2008a, pp. 1-35; FTHLICC 2009, pp. 1-38; FTHLICC 2010, pp. 1-33). These reports document and summarize the progress member agencies have made towards implementation of the Planning Actions identified in Rangewide Management Strategy (FTHLICC 2003a, pp. 25-32). The reports indicate that progress by signatory agencies has been made in the following areas: (1) Designation of the five Management Areas and the one Research Area; (2) requiring actions by permittees to follow the avoidance, minimization, and mitigation measures outlined in the Rangewide Management Strategy; (3) rehabilitating damaged and degraded habitat within the Management Areas; and (4) purchase of lands for flat-tailed horned lizard conservation from willing sellers. Although some lower priority actions (tasks), such as research on natural barriers, remain outstanding, the committee reports that nearly all tasks, many of which are ongoing or multi-year actions, are on schedule (FTHLICC 2010, pp. 21-25). Thus, despite being a voluntary agreement, the signatory agencies generally have been implementing the Interagency Conservation Agreement and associated Rangewide Management Strategy by meeting regularly, working to implement the measures of the Rangewide Management Strategy including providing personnel, developing and distributing public information, and providing ongoing review and feedback.

Coachella Valley Multiple Species Habitat Conservation Plan (Coachella Valley MSHCP)

Our past assessments of the status of the flat-tailed horned lizard, particularly the 2003 withdrawal (68 FR 331), addressed the Coachella Valley in detail; thus, for consistency we again address the Coachella Valley here and elsewhere in this document. Since the 2003 withdrawal, and even since our June 28, 2006, withdrawal (71 FR 36745), we have issued an incidental take permit for a large, regional HCP in the Coachella Valley. The Coachella Valley MSHCP is a large-scale, multi-jurisdictional habitat conservation plan encompassing about 445,156 ha (1.1 million ac) in the Coachella Valley of central Riverside County. An additional 27,923 ha (69,000 ac) of Tribal reservation lands distributed within the plan area boundary are not included in the Coachella Valley MSHCP. The Coachella Valley MSHCP addresses 27 listed and unlisted “covered species,” including the flat-tailed horned lizard. On October 1, 2008, the Service issued a single incidental take permit (TE-104604-0) under section 10(a)(1)(B) of the Act to 19 permittees under the Coachella Valley MSHCP for a period of 75 years. Participants in the Coachella Valley MSHCP include eight cities (Cathedral City, Coachella, Indian Wells, Indio, La Quinta, Palm Desert, Palm Springs, and Rancho Mirage); the County of Riverside, including the Riverside County Flood Control and Water Conservation District, Riverside County Parks and Open Space District, and Riverside County Waste Management District; the Coachella Valley Association of Governments; Coachella Valley Water District; Imperial Irrigation District; California Department of Transportation; California State Parks; Coachella Valley Mountains Conservancy; and the Coachella Valley Conservation Commission (the created joint powers regional authority). The Coachella Valley MSHCP was designed to establish a multiple species habitat conservation program that minimizes and mitigates the expected loss of habitat and incidental take of covered species, including flat-tailed horned lizard (USFWS 2008, pp. 1-207, and Appendix A, pp. 298-328). The Coachella Valley MSHCP is also a “Subregional Plan” under the State of

California's Natural Community Conservation Planning (NCCP) Act, as amended.

The permit covers incidental take resulting from habitat loss and disturbance associated with urban development and other proposed covered activities. These activities include public and private development within the plan area that require discretionary and ministerial actions by permittees subject to consistency with the Coachella Valley MSHCP policies. An associated Management and Monitoring Program is also included in the Coachella Valley MSHCP and identifies specific management actions for the conservation of the flat-tailed horned lizard and its habitat.

The Coachella Valley MSHCP identifies a reserve system that, upon full implementation, will establish 21 conservation areas that are either adjacent to each other or are linked by biological corridors. The acquisition program for the plan's reserve system is designed to conserve 52,484 ha (129,690 ac) during the first 30 years. This program is to be implemented such that acquisitions occur commensurate (in “rough step”) with impacts from urban development that is covered under the plan.

The flat-tailed horned lizard is now known to occur only at two locations within the Coachella Valley MSHCP area, the Thousand Palms and Dos Palmas conservation areas (CVCC 2010, p. 13) (see also

Description of Specific “Populations”

section below). Table 2 describes the amount of flat-tailed horned lizard habitat conserved and identified to be conserved through implementation of the Coachella Valley MSHCP. Additionally, plan implementation is expected to limit impacts of development and other covered activities on lands within conservation areas but that have not yet been acquired for conservation as part of the Coachella Valley MSHCP reserve system. The plan also designates one core habitat area (as used in that plan, this refers to an area that is large enough to maintain a self-sustaining population)—the Thousand Palms conservation area—and commits to establishing two more self-sustaining populations in other parts of the reserve system, if feasible, to benefit the flat-tailed horned lizard. Because of the distances separating appropriate parts of the reserve system, relocation of flat-tailed horned lizards will be required to re-establish or enhance populations in suitable habitat areas that have the potential to, but currently do not, support self-sustaining populations. Additionally, the plan calls for Management and Monitoring Programs that are expected to conserve this species in the plan area. Required management activities include limiting activities that degrade flat-tailed horned lizard habitat, evaluation and management of edge effects and other impacts through adaptive management, control of invasive species where necessary, and restoration and enhancement of degraded habitat as necessary according to monitoring results (CVAG 2007, p. 9-123). In our evaluation of the potential impacts of the plan's implementation on the flat-tailed horned lizard (USFWS 2008, p. 178), we concluded: “After reviewing the current status of this species, environmental baseline for the action area, effects of the proposed action, and cumulative effects, it is the Service's biological opinion that the action, as proposed, is not likely to jeopardize the continued existence of the flat-tailed horned lizard. Loss of the Coachella Valley population would have a negligible [effect] on the status of the species as a whole, since it makes up approximately 1 percent of the current range of the flat-tailed horned lizard. Persistence of the species in the Plan area is likely only with effective Plan implementation.”

Table 2—Area of Flat-tailed Horned Lizard Habitat Conserved, Anticipated To Be Conserved, Impacted, and Anticipated To Be Impacted Through Implementation of the Coachella Valley MSHCP

Criterion (source)

Thousand Palms

Dos Palmas

Flat-tailed horned lizard habitat area conserved at permit issuance in 2008 (CVAG 2007, p. 9-115)

1,318 ha (3,256 ac)

608 ha (1,503 ac)

Additional flat-tailed horned lizard habitat area conserved in 2008 (CVCC 2009, p. 79)

274 ha (678 ac)

107 ha (265 ac)

Additional flat-tailed horned lizard habitat area conserved in 2009 (CVCC 2010, pp. 39 & 51)

8 ha (20 ac)

0 ha (0 ac)

Total flat-tailed horned lizard habitat area under conservation through 2009 (calculated)

1,600 ha (3,954 ac)

715 ha (1,768 ac)

Total flat-tailed horned lizard habitat area expected to be conserved by MSHCP implementation (CVAG 2007, p. 9-115)

1,707 ha (4,219 ac)

2,078 ha (5,134 ac)

Percent flat-tailed horned lizard habitat area conserved through 2009 compared to amount required upon full implementation of the plan (calculated)

94%

34%

Area of flat-tailed horned lizard habitat impacted by permitted activities through 2009 (CVCC 2009, p. 79; CVCC 2010, pp. 39 & 51)

0 ha (0 ac)

0 ha (0 ac)

Area of flat-tailed horned lizard habitat anticipated to be impacted by permitted activities (CVAG 2007, p. 9-115)

44 ha (108 ac)

163 ha (403 ac)

Percent flat-tailed horned lizard habitat area anticipated to be impacted compared to total area of flat-tailed horned lizard habitat in conservation area (calculated)

2%

7%

Lower Colorado River Multi-Species Conservation Plan (Lower Colorado River MSCP)

The Lower Colorado River MSCP is a joint effort by Federal and non-Federal (State, local, and private) entities with management authority for storage, delivery, and diversion of water; hydropower generation, marketing, and delivery; and land management or Native American Trust responsibilities along the Lower Colorado River, to address regulatory requirements under sections 7, 9, and 10 of the Act for their activities. We issued the 50-year permit (TE-086834) on April 4, 2005. Most of the activities addressed by the Lower Colorado MSCP are outside the range of the flat-tailed horned lizard. The flat-tailed horned lizard habitat contained within the Lower Colorado River MSCP

planning area is under control of agencies, especially the Bureau of Reclamation, that have agreed to implement the Rangewide Management Strategy (USFWS 2005, p. 202).

Implementation of the Lower Colorado River MSCP is expected to provide for the acquisition and long-term protection of 230 acres of existing flat-tailed horned lizard habitat that is currently unprotected. This action is compensation for anticipated impacts to approximately 128 acres of flat-tailed horned lizard habitat (USFWS 2005, pp. 201-202). Purchase of protected habitat, potentially near the Dos Palmas reserve area, is scheduled to start in 2011 (BOR 2010, p. 274). Additionally, activities covered under the permit will be designed to avoid or minimize effects to the species and its habitat in accordance the conservation needs identified in the Rangewide Management Strategy (USFWS 2005, pp. 201-202).

We found that implementation of the Lower Colorado River MSCP was “Not Likely to Jeopardize the Continued Existence of the Species” (USFWS 2005, p. 202), noting “The habitat area that would be included [under the plan] is not a significant amount of the available habitat for the species. * * * Research and monitoring of the species within the [Lower Colorado River MSCP] area will contribute to understanding the species, its distribution, and habitat needs. * * * [and] There are not likely to be any adverse effects to the species' conservation elsewhere in the range from the issuance of an incidental take permit for the [Lower Colorado River MSCP]” (USFWS 2005, p. 202).

Population Dynamics

Flat-tailed horned lizards are difficult to detect, which limits the effectiveness of surveys for the species (FTHLICC 2003a, pp. 9, 65; Grant and Doherty 2007, p. 1050). As a result, not only is presence and especially absence difficult to determine, but determining the size, trend, and demography of populations is problematic as well. The history of flat-tailed horned lizard monitoring and the shortcomings of the techniques used are described in the Rangewide Management Strategy (FTHLICC 2003a, p. 64) and our 2003 withdrawal document (68 FR 332-333). Monitoring using more rigorous data collection and analytical methodologies has been conducted as part of the implementation of the Rangewide Management Strategy (FTHLICC 2003a, pp. 64-66; FTHLICC 2008b, pp. 1-38). The results from this monitoring effort are described below.

As detailed in the Flat-tailed Horned Lizard Monitoring Plan (FTHLICC 2008b, pp. 1-38), flat-tailed horned lizard monitoring consists of two surveys used in tandem: (1) Occupancy estimation surveys and (2) demographic plot surveys. Occupancy estimation was designed to determine whether the distribution (but not numbers of individuals or densities) of flat-tailed horned lizards in the management and research areas is stable, increasing, or decreasing. This component of the monitoring was meant to detect large-scale changes in the status of flat-tailed horned lizard distribution in the Management Areas. The monitoring of demographic plots was designed to delineate flat-tailed horned lizard population dynamics and trends by estimating abundance each summer and yearly survival, recruitment, and population growth rate between years. This component was meant to gather more in-depth information on a smaller number of plots. However, the demographic plots were non-randomly established within areas known or suspected to support greater densities of flat-tailed horned lizards. The Management Areas overall were selected because they provided generally high-quality flat-tailed horned lizard habitat. However, the use of the two complementary survey types, one dispersed and coarse and the other focused and narrow, allows managers to draw, with caution, more detailed conclusions about an entire Management Area than they could have otherwise done by interpreting just one of the survey types alone. Below we summarize the information available from these monitoring efforts (source: USFWS 2010a, pp. 1-76).

Occupancy surveys were conducted at West Mesa (2005 and 2009), East Mesa (2006), Yuha Desert (2008), and Ocotillo Wells State Vehicular Recreation Area (SVRA) (2006-2009). Separate occupancy analyses of these areas were conducted based on three survey methodologies: visual observations of flat-tailed horned lizards, lizard scat observations, and a combination of visual and scat observations. Multi-year analyses also were conducted for a subset of 53 plots in Ocotillo Wells SVRA that were surveyed annually from 2006 to 2009. Our analysis indicates the combined visual-and-scat surveys were the most likely to correctly yield a statistically significant result (i.e., this survey methodology had the greatest statistical power). Although there are no comparable historical data with which to provide context, our analysis suggests that the level of occupancy of flat-tailed horned lizards within the surveyed areas seemed relatively high at all sites. For example, visual-and-scat survey results show that flat-tailed horned lizards occupied at least 80 percent of the Management Areas in the years surveyed, except in the West Mesa Management Area in 2005, which had a low level of survey effort that year. Additionally, results from the 53-plot subset with multi-year data from 2006 to 2009 suggested that the level of flat-tailed horned lizard occupancy stayed about the same or may have even increased slightly over time. Moreover, our analysis showed considerable support to conclude that there was no linear decline in the proportion of survey plots occupied by flat-tailed horned lizards. These results only reflect the occupancy of flat-tailed horned lizards within the areas surveyed and do not necessarily reflect the level of occupancy throughout the range of the species; nevertheless, we conclude from the above results that the level of occupancy within the survey areas is not low, and that there is no indication of a decline.

Data from the demographic plots were gathered from six 9-hectare (22.2-acre) plots at the following flat-tailed horned lizard Management Areas: East Mesa (1 plot, 2007-2009), West Mesa (1 plot, 2007-2009; 1 plot, 2008-2009), Yuha Desert (1 plot, 2007-2009), and Yuma Desert (2 plots, 2008-2009). Hatchlings were captured at all Management Areas except East Mesa (which was surveyed prior to the time that flat-tailed horned lizards eggs would have been likely to have hatched), indicating that flat-tailed horned lizards were reproducing. The presence of hatchlings during 2008, and especially 2009, suggested that reproductive conditions were favorable in those years.

Because of the complexities of analyzing a cryptic species, we used two methodologies to calculate flat-tailed horned lizard abundance. Because the surveyed plots were not closed (meaning flat-tailed horned lizards could move in and out of the areas being surveyed), we used two different methods (calculations) to estimate the “effective survey area” so that we could translate abundance (number of individuals) into densities (number of individuals per unit area). Using the first method (using a mean maximum distance moved buffer strip to estimate effective survey area), the density of adult flat-tailed horned lizards ranged from 0.3 to 3.3 individuals per ha (0.1 to 1.3 individuals per ac), while the second method (using a hierarchical, spatially indexed capture-recapture model to estimate effective survey area) yielded a range from 0.7 to 4.4 individuals per ha (0.3 to 1.8

individuals per ac). The results from the second method are likely to be more realistic because they incorporated additional spatial information.

Other estimates of density of flat-tailed horned lizards are available in the scientific literature, but comparisons between and among the different studies (including the recent monitoring) are confounded by differing survey and analysis methodologies. Nevertheless, the above densities at the three California Management Areas were generally within the range of estimates reported by Grant (2005, pp. 39-40) during 2002-2004. Similarly, the densities of adult flat-tailed horned lizards at the Yuma Desert Management Area reported above were generally similar to the ranges of estimates presented by Young and Young (2000, p. 28) during 1997-1998, Young

et al.

(2004b, p.

i

) during 2003, and Young and Royle (2006, p. 9) in 2005. Comparisons to even earlier estimations of flat-tailed horned lizard densities, although even more tenuous because of differing methodologies, are also within similar ranges. Despite similar ranges in densities reported from the various studies through time, the increased statistical and methodological rigor of recent efforts has reduced the level of uncertainty in the results. Thus, these recent density estimates are an improvement over older estimates.

The available data indicate that flat-tailed horned lizard abundances and densities have remained relatively stable from 2007 to 2009; however, with only 3 years of standardized monitoring, these data cannot yet provide meaningful inferences about long-term trends. Additionally, no abundance or density information is available for the lower-quality habitat areas outside the demographic plots. However, the complementary coarse-scale occupancy survey data mentioned above suggests flat-tailed horned lizards are widely distributed spatially and, in at least at one Management Area, temporally consistent. This conclusion suggests that flat-tailed horned lizard population trends in the surveyed lower-quality habitat areas are not dissimilar to those of the surveyed higher-quality habitat areas. Moreover, because the recent (2007-2009) and older (1997-2005) density estimates are all generally within similar ranges, this suggests the overall density of flat-tailed horned lizards within the surveyed Management Areas has not markedly decreased over the past decade or so. Thus, with the previously mentioned caveats in mind, we conclude that flat-tailed horned lizard populations in the Management Areas are not low and have not declined since 2007, and probably not declined since 1997.

Description of Specific “Populations”

As stated earlier, we have divided the current range of the flat-tailed horned lizard into four populations based on geographic locales. The 2003 Rangewide Management Strategy includes a GIS-based map (FTHLICC 2003a, p. 5) of the “current distribution” of the flat-tailed horned lizard. Except for the Coachella Valley Population, where the flat-tailed horned lizard is now limited to two occurrences, we used the GIS data as a basis for our assessment of the distribution of flat-tailed horned lizard populations. A summary of these populations is presented below.

Coachella Valley Population

(California)—The “current distribution” within the Coachella Valley as defined by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5) does not represent the best scientific distribution information available for this region. Urban and agricultural development has continued in the Coachella Valley, and there are many areas of unsuitable or degraded habitat. In addition to areas of unsuitable habitat, many of which serve as a barrier to flat-tailed horned lizard movement, other potential manmade barriers exist, including several major highways, a railway, and canals. The only area within the Coachella Valley proper that is now known to be occupied by flat-tailed horned lizards is in the Thousand Palms reserve (CVCC 2010, p. 13). Other areas of potentially suitable habitat occur in the region, including areas that were formerly known to be occupied (Barrows

et al.

2008, p. 1891), although recent surveys have not detected any flat-tailed horned lizards (CVCC 2010, p. 13). Thus, the “current distribution” as defined by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5) does not accurately reflect the area occupied by flat-tailed horned lizards in the Coachella Valley; as such, we do not use a GIS-based assessment for the Coachella Valley as we do for the other geographical “populations.”

The Coachella Valley MSHCP is the primary driver of monitoring and management activities for the Coachella Valley Population of the flat-tailed horned lizard because the Rangewide Management Strategy does not include any Management Areas in this region. The Coachella Valley Population area is the smallest of the four geographic “populations,” and we primarily identify it as a separate population to be consistent with our past analyses. Flat-tailed horned lizards also occur in the vicinity of the Dos Palmas Preserve near the northeast shore of the Salton Sea (Turner and Medica 1982, p. 817; FTHLICC 2003a, pp. 2-6; CVCC 2010, p. 13). The Dos Palmas population is small and likely isolated from other populations because of the presence of the Salton Sea to the west; canals, roads and urban and agricultural development to the northwest; and canals, roads and urban and agricultural development to the southeast. However, not all of these barriers are likely to completely restrict flat-tailed horned lizard movement (see the Factor E discussion, below). The genetic affinities of the Dos Palmas population are not known. Geographically, the flat-tailed horned lizards at Dos Palmas Preserve could arguably be considered part of either the Western Population or Eastern Population (see below); however, because the true affinities of this population are not known, and because the Dos Palmas reserve area is covered under the Coachella Valley MSHCP and its associated monitoring and management, herein we consider the Dos Palmas flat-tailed horned lizards to be part of the Coachella Valley Population. The area of flat-tailed horned lizard habitat in the Coachella Valley Population is about 3,785 ha (9,353 ac) (see Table 2).

Western Population

(California and Baja California)—This population includes flat-tailed horned lizards in the areas west of the Salton Sea, the Imperial Valley, and the Mexicali Valley. Using a GIS-based assessment to estimate the area of this portion of the “current distribution” as defined by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5), we estimated that the Western Population occupies 341,989 ha (845,073 ac). Of this acreage, approximately 253,020 ha (625,226 ac) is within the United States. Within the U.S. portion of the Western Population, approximately 48,262 ha (119,258 ac), or about 19 percent, is non-Federal or non-State owned, or is more likely to be developed. The habitat within this area is mostly intact except for a few developed areas, but as discussed in the “Barriers and Small Populations” section under Factor E, potential manmade barriers to flat-tailed horned lizard movement (in addition to areas of urban and agricultural development) include Interstate 8; State Routes 78, 86, and 98; two railways; the fence and other activities along the international border in the United States, and Mexico Federal Highway 2 in Mexico. The Rangewide Management Strategy designates three Management Areas in this population area, including Borrego Badlands, West Mesa, and Yuha Desert

(see Table 1), and a research area at the Ocotillo Wells SVRA. Much of the westernmost portion of this population is within Anza-Borrego Desert State Park. Additionally, private lands are scattered throughout the U.S. portion, with large aggregations in the Borrego Springs area and in the vicinity of (but outside of) Ocotillo Wells SVRA. The range of the flat-tailed horned lizard in this population also extends southward into Mexico, crossing the international border at the Yuha Desert and continuing south along the east side of the Peninsular Ranges and west of Laguna Salada in Baja California (FTHLICC 2003a, pp. 2-5). The status of the population in this portion of the range in Mexico is poorly known, but there have been few substantive changes to the landscape in this area. Additionally, flat-tailed horned lizards were observed recently near Cerro Prieto, Baja California, which is east of the Sierra de Los Cucapahs (Sierra Cucapá) and west of the agricultural areas of the Mexicali Valley (A. Calvo Fonseca, Pronatura Noroeste,

in litt.

2010). This recent detection is outside of the current distribution as depicted in the Rangewide Management Strategy (FTHLICC 2003a, p. 5).

Eastern Population

(California and Baja California)—This population includes flat-tailed horned lizards in the areas east of the Salton Sea and the Imperial Valley but west of the Colorado River. While the isolated population at Dos Palmas Preserve could be included as part of either the Eastern Population or the Coachella Valley Population based on its geographic location, for the purposes of our analysis of threats to the species we consider the Dos Palmas Preserve population to be part of the Coachella Valley Population because of the similarity of potential threats when compared to the populations in the Coachella Valley, and its inclusion within the Coachella Valley MSHCP plan area. Using a GIS-based assessment to estimate the area of the Eastern Population portion of the “current distribution” (as defined by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5)), we estimated that the Eastern Population occupies 169,617 ha (419,133 ac). Of this acreage, approximately 146,121 ha (361,073 ac) is within the United States. Within the U.S. portion of the Eastern Population, approximately 5,844 ha (14,441 ac), or about 4 percent, is non-Federal or non-State owned, or is more likely to be developed. The area occupied by the Eastern Population is mostly intact except for a few developed areas, but potential manmade barriers to flat-tailed horned lizard movement (in addition to areas of urban and agricultural development) include Interstate 8, State Routes 78 and 98, the All-American Canal and the Coachella Canal, and the international border fence in the United States (see “Barriers and Small Populations” section under Factor E, below). The Rangewide Management Strategy designated the East Mesa Management Area within the area occupied by the Eastern Population (see Table 1). The geographic extent of the Eastern Population also includes the Algodones Dunes (also known as the Imperial Sand Dunes or Glamis Sand Dunes), a portion of which is designated Wilderness, and a narrow strip of habitat south of the international border at the southern edge of the Algodones Dunes (FTHLICC 2003a, pp. 2-5). The portion of the Eastern Population area in Mexico is bound by agricultural development (unsuitable habitat) on the west, south, and east. The status of the portion of the Eastern Population in Mexico is poorly known, but flat-tailed horned lizards were observed recently in this area (A. Calvo Fonseca,

in litt.

2010).

Southeastern Population

(Arizona and Sonora)—This population includes flat-tailed horned lizards in the areas east of the Colorado River, extending from Yuma, Arizona, south and east to the Gulf of California in northwestern Mexico. In Arizona, the flat-tailed horned lizard occurs in Yuma County, ranging over the Yuma Desert south of the Gila River and west of the Gila and Butler Mountains (Rorabaugh

et al.

1987, p. 104; FTHLICC 2003a, pp. 2-6). The Rangewide Management Strategy designated the Yuma Desert Management Area within the area occupied by the Southeastern Population (see Table 1). In Mexico, the flat-tailed horned lizard ranges from the international border in the Yuma Desert south and east through the Pinacate Region to the sandy plains around Puerto Peñasco and Bahia de San Jorge along the Gulf of California (Johnson and Spicer 1985, p. 13; Gonzáles-Romero and Alvarez-Cardenas 1989, p. 519; FTHLICC 2003a, pp. 2-5). About 60 percent of the flat-tailed horned lizard habitat in Sonora lies within two Mexican Federal natural protected areas: the Upper Gulf of California and Colorado Delta Biosphere Reserve, and the Pinacate and Gran Desierto de Altar Biosphere Reserve (CEDO 2001, p. 3).

Using a GIS-based assessment to estimate the area of this portion of the “current distribution” as defined by the Rangewide Management Strategy (FTHLICC 2003a, pp. 3-5), we estimated that the area occupied by the Southeastern Population is 1,073,551 ha (2,652,802 ac), by far the largest of the four population areas. Of this acreage, approximately 67,922 ha (167,839 ac) is within the United States. Within the U.S. portion of the Southeastern Population, approximately 5,158 ha (12,746 ac), or about 8 percent, is privately owned; an additional 5,832 ha (14,411 ac), or about 9 percent, is State of Arizona-owned lands. The habitat within the Southeastern Population area is mostly intact except for a few developed areas, but potential barriers to flat-tailed horned lizard movement (in addition to areas of urban and agricultural development) include Interstate 8 and the Yuma Areas Service Highway in the United States; the international border (combined with Mexico Federal Highway 2); Mexico Federal Highway 8; and a railway in Mexico (see “Barriers and Small Populations” section under Factor E, below).

In summary, using a GIS-based assessment to estimate the size of the current distribution of the flat-tailed horned lizard as defined by the Rangewide Management Strategy (FTHLICC 2003a, p. 5), we estimated that the three population areas (excluding the Coachella Valley Population) comprise roughly 1,585,000 ha (3,916,600 ac), of which approximately 467,000 ha (1,154,000 ac) (less than 30 percent) is within the United States and approximately 1,100,000 ha (2,718,000 ac) (more than 70 percent) is within Mexico. The area of flat-tailed horned lizard habitat occupied or likely to be occupied that already is or is expected to be conserved in the Coachella Valley Population is about 3,785 ha (9,353 ac) (see Table 2).

Previous Federal Actions

In 1982, we first identified the flat-tailed horned lizard as a category 2 candidate species for listing under the Act (47 FR 58454; December 30, 1982). Category 2 candidate species were “taxa for which information now in possession of the Service indicates that proposing to list the species as Endangered or Threatened is possibly appropriate, but for which sufficient data on are not currently available to biologically support a proposed rule” (47 FR 58454). We again identified the flat-tailed horned lizard as a category 2 candidate species in our 1985 notice of review (50 FR 37958; September 18, 1985). In 1989, we elevated the species to category 1 status (54 FR 554; January 6, 1989). Category 1 included species “for which the Service currently has substantial information on hand to support the biological appropriateness

of proposing to list as endangered or threatened” (54 FR 554). We maintained the category 1 status for the flat-tailed horned lizard in our 1991 notice of review (56 FR 58804; November 21, 1991).

On November 29, 1993, we published in the

Federal Register

a proposed rule to list the flat-tailed horned lizard as a threatened species under the Act (58 FR 62624). On February 22, 1994 (59 FR 8450), we published a notice reopening the public comment period and announcing that we had scheduled a public hearing on March 22, 1994, in Imperial, California, in response to a request from the public. Our November 15, 1994, candidate notice of review stated that we had proposed to list the species as threatened (59 FR 58982).

Subsequently, the passage of Public Law 104-6, 109 Stat. 73 on April 10, 1995, resulted in a delay in our final listing determination for the flat-tailed horned lizard. Although the statute's primary purpose was to provide additional funds for overseas military operations, it also included a rider that withdrew funding for listing determinations. Through a series of moratoria, funding restrictions, and continuing resolutions, this restriction in use of funds remained in effect until April 26, 1996, when the Omnibus Appropriations Act was enacted (Pub. L. 104-134, 110 Stat. 1321, (1996)), which contained a moratorium on certain listing activities but allowed the President to waive the moratorium. On April 26, 1996, President Clinton suspended the provision limiting implementation of Section 4 of the Act (61 FR 24667; May 16, 1996). Earlier in 1996, our notice of review had indicated that we had proposed to list the species as threatened (61 FR 7596; February 28, 1996).

On January 21, 1997, the Bureau of Land Management (BLM) announced in the

Federal Register

that the draft Flat-tailed Horned Lizard Rangewide Management Strategy was available for public comment (62 FR 3052). On May 16, 1997, in response to a lawsuit filed by the Defenders of Wildlife and other plaintiffs to compel us to make a final listing determination on the flat-tailed horned lizard, the District Court in Arizona ordered us to issue a final listing decision within 60 days. In June 1997, several State and Federal agencies, including the Service, signed an Interagency Conservation Agreement committing to implement the recently finalized Flat-tailed Horned Lizard Rangewide Management Strategy (FTHLICC 1997, pp. 1-106). Pursuant to the Interagency Conservation Agreement, cooperating parties agreed to take voluntary steps aimed at “reducing threats to the species, stabilizing the species' populations, and maintaining its ecosystem” (

see

FTHLICC 2003a, p. 80).

On July 15, 1997, we issued a final decision to withdraw the proposed rule to list the flat-tailed horned lizard as a threatened species (62 FR 37852). We based the withdrawal on three factors: (1) Population trend data did not conclusively demonstrate significant population declines; (2) Some of the threats to the flat-tailed horned lizard habitat had abated since the proposed rule was issued; and (3) Our conclusion that the recently approved Interagency Conservation Agreement would ensure further reductions in threats (62 FR 37852).

On December 30, 1997, the Defenders of Wildlife and others filed a complaint in the U.S. District Court for the Southern District of California challenging our 1997 withdrawal of the proposed rule. On June 16, 1999, the District Court upheld our decision to withdraw the proposed listing rule. The District Court's decision was appealed and on July 31, 2001, the Ninth Circuit Court of Appeals vacated the previous ruling of the District Court. The case was remanded back to the Secretary because: (1) The withdrawal of the proposed rule did not expressly consider whether the flat-tailed horned lizard is likely to become an endangered species within the foreseeable future in a significant portion of its range; and (2) The withdrawal of the proposed rule did not “address the lizard's viability in a site-specific manner with regard to the putative benefits of the Interagency Conservation Agreement.” In accordance with the Appeals Court's ruling, we published a document in the

Federal Register

on December 26, 2001, reinstating the 1993 proposed rule and opening a 120-day public comment period (66 FR 66384).

On May 30, 2002, we published a document in the

Federal Register

reopening the public comment period for an additional 60 days (67 FR 37752) and announced that we would be holding public hearings in El Centro, California, on June 19, 2002. On September 24, 2002, we published in the

Federal Register

another document (67 FR 59809) announcing the reopening of the public comment period for an additional 15 days to allow for peer review, additional public comment on the proposed rule, and submittal of information that became available since our 1997 withdrawal.

On January 3, 2003, we again published in the

Federal Register

a decision to withdraw the November 29, 1993, proposed rule to list the flat-tailed horned lizard as a threatened species (68 FR 331). The Service found the lizard to be “in danger of extirpation in the Coachella Valley” (68 FR 348); however, we determined that the Coachella Valley is not a significant portion of the species' range. We concluded in the January 3, 2003, withdrawal that the flat-tailed horned lizard populations on either side of the Imperial Valley-Salton Sea and in Arizona were not likely to become endangered in the foreseeable future and that listing the species was not warranted.

The Tucson Herpetological Society and others filed a complaint with the District Court for the District of Arizona challenging the January 3, 2003, withdrawal of the proposed rule. In a ruling issued on August 30, 2005, the District Court for the District of Arizona issued an order granting plaintiffs' motion for summary judgment, citing our failure to specifically evaluate the lost habitat of the flat-tailed horned lizard, and whether the amount of lost habitat represented a significant portion of the species' range. On December 7, 2005, we published a document in the

Federal Register

reinstating the 1993 proposed rule (70 FR 72776). On March 2, 2006, we announced in the

Federal Register

that we were reopening the public comment period on the 1993 proposed rule for 14 days for the purpose of soliciting comments and information relevant to the specific issue identified in the District Court's November 2005 ruling (

i.e.,

whether the flat-tailed horned lizard's lost historical habitat rendered the species likely to become in danger of extinction in the foreseeable future throughout all or a significant portion of its range) (71 FR 10631). On April 21, 2006, we announced in the

Federal Register

an additional public comment period on the 1993 proposed rule from April 21, 2006, to May 8, 2006 (71 FR 20637).

After re-examining the lost historical habitat of the flat-tailed horned lizard in relation to our January 3, 2003, withdrawal, we determined that the lost historical habitat is not a significant portion of the species' range, and its loss does not result in the species likely becoming endangered in the foreseeable future throughout all or a significant portion of its range. We published our decision in the

Federal Register

on June 28, 2006, to once again withdraw the November 29, 1993, proposed rule to list the flat-tailed horned lizard as a threatened species (71 FR 36745).

Following a supplemental complaint from Tucson Herpetological Society and others challenging the 2006 withdrawal

of the proposed rule to list the flat-tailed horned lizard under the Act, the United States District Court for the District of Arizona (the District Court) granted summary judgment in favor of the Secretary of the Interior (

Tuscon Herpetological Society

v.

Kempthorne,

04-CV-00075-PHX-NVW); however, this ruling was appealed to the Court of Appeals for the Ninth Circuit. In a ruling issued on May 18, 2009, the Court of Appeals for the Ninth Circuit reversed the District Court's ruling when it determined that in the context of the analysis of whether the lizard's lost historical range constituted a significant portion of the species' range, the administrative record did not support what the Court of Appeals for the Ninth Circuit viewed as the Service's conclusion that flat-tailed horned lizard populations were stable and viable throughout most of its current range.

On November 3, 2009, the District Court remanded the 2006 withdrawal to the Service for further consideration and reinstated the 1993 proposal to list the species. The District Court ordered the Service to complete this reconsideration in accordance with the deadlines set forth in 16 U.S.C. 1533(b). On March 2, 2010, we published a notice in the

Federal Register

announcing the reinstatement of the 1993 proposed rule, the reopening of the public comment period for 60 days, and the scheduling of public hearings (75 FR 9377). Public hearings were held in Palm Desert, California, on March 23, 2010, and Yuma, Arizona, on March 24, 2010.

Summary of Factors Affecting the Species

Section 4 of the Act (16 U.S.C. 1531

et seq.

) and the regulations that implement the listing provisions of the Act (50 CFR part 424) set forth the procedures for adding species to the Federal Lists of Endangered and Threatened Wildlife and Plants. A species may be determined to be an endangered or threatened species due to one or more of the five factors described in section 4(a)(1) of the Act (Factors A through E).

We evaluated threats to the flat-tailed horned lizard under the five listing factors in the 1993 proposed rule to list the flat-tailed horned lizard as threatened under the Act (58 FR 62624). Subsequent documents in 1997 and 2003 withdrawing the proposed rule to list the species included additional evaluations (62 FR 37852; 68 FR 331). The 2003 document withdrawing the proposed rule was the most comprehensive and the most recent five-factor analysis. The 2006 document withdrawing the proposed rule (71 FR 36745) did not address the five factors in detail because its scope was limited by a court order (

see

Previous Federal Actions section). In this document, we use the best scientific and commercial data available to evaluate current potential threats to flat-tailed horned lizard and its habitat rangewide per the five listing factors, and we provide brief summaries of the 1993 and 2003 evaluations for context.

A. The Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range

For this factor, we evaluated the present (current) or threatened (anticipated) impacts that may be affecting the habitat or range of the flat-tailed horned lizard. This factor does not address historical or past actions that resulted in destruction, modification, or curtailment of the species' habitat or range. Past actions that destroyed, modified, or curtailed the species' habitat or range are not threats in and of themselves. Any persisting ramifications of such past actions that may be threats to the species are addressed under Factor E (other natural or manmade threats), below. However, for Factor A, we do look to past actions to inform our evaluation of potential future threats affecting the species' habitat or range in that the history of past actions allows us to predict the likelihood of such actions continuing into the foreseeable future.

In the 1993 proposed rule (58 FR 62625-62626), we identified historical flat-tailed horned lizard habitat losses that resulted in the curtailment of the species' range under Factor A. We noted threats that were current or anticipated at that time, including agricultural and urban development, off-highway vehicle (OHV) use, geothermal energy development, sand and gravel extraction operations, military training activities, and construction of roads and utility corridors. We also mentioned that flat-tailed horned lizard habitat had been fragmented, causing isolation of populations (curtailment of the species' range) (see below for additional discussion on fragmentation). Additionally, the 1993 proposed rule also mentioned gold mining as a potential threat. There are currently no gold mines in flat-tailed horned lizard habitat, and we are not aware of any proposals for new gold mines; therefore, we do not expect gold mines to become a threat in the foreseeable future.

In the 2003 withdrawal document (68 FR 341-345), we found that current and anticipated urban and agricultural development was limited to a few, small areas and did not constitute a significant threat to the species. However, we did state that past agricultural, urban, and associated infrastructural development (such as canals and roads) had fragmented the species' range, which we discuss below as a separate threat under Factor A.

Fragmentation and Past Habitat Loss

Because of our past treatment of fragmentation in our previous rules, we are providing a discussion of

fragmentation

as a term and its application to the five-factor analysis for the flat-tailed horned lizard. This discussion should: (1) Provide a clear definition of the term that we use in this document, and (2) acknowledge that our lack of clarity for this term in past documents may have resulted in unanswered questions as to how the flat-tailed horned lizard may have been affected by historical development in the Salton Trough. Because of the connection between fragmentation and historical habitat loss, we also describe how historical habitat loss was addressed in past assessments.

In the 2003 withdrawal document, we defined fragmentation as the “breaking up of a habitat or ecosystem into smaller parcels” (68 FR 341). This definition is similar to the more detailed version used by Wilcove

et al.

(1986, p. 237) who defined habitat fragmentation as occurring “when a large expanse of habitat is transformed into a number of smaller patches of smaller total area, isolated from each other by a matrix of habitats unlike the original.” Thus, fragmentation is a process, one that inextricably involves habitat loss (Fahrig 1999, p. 87). However, in addition to the effects associated with habitat loss, fragmentation also includes the effects associated with the fractured nature of that habitat

after its transformation

(Fahrig 2003, p. 487). The implication is that the biological properties of the remaining, small, isolated patches of habitat have changed during or as a result of the fragmentation of the habitat (van den Berg

et al.

2001, p. 225). In other words, after some portion of the habitat of a species has been destroyed, that species may be impacted by one or more secondary effects (threats) associated with reduction in the size of remaining habitat patches (or the populations of the species therein) and the isolation of those patches (and populations) from each other (Andrén 1994, p. 355). Thus, the effects of fragmentation include: (1) The effects associated with the ongoing loss of habitat; and (2) the subsequent, secondary effects that are the current ramifications of past habitat loss.

Because multiple secondary effects may be related or correlated to each other (Fahrig 2003, pp. 491-492), the term fragmentation, as it has been used in the scientific literature and by the Service in past assessments of this species, is ambiguous (Haila 2002, p. 321). Because of this ambiguity, in applying the Act's five listing factors to the flat-tailed horned lizard, we will address current and anticipated habitat loss under Factor A, and the relevant, identifiable secondary effects (including threats associated with fragmentation) to the species under Factor E.

Our past assessments describe in detail and attempted to quantify the historical development in the Salton Trough (58 FR 62626; 62 FR 37857; 68 FR 341-345; 71 FR 36751), as did the scientific literature (such as Johnson and Spicer 1985, p. 38, 45-48; Rorabaugh

et al.

1987, p. 106; Hodges 1995, pp. 1-18; Hodges 1997, pp. 1-16; Piest and Knowels 2002, pp. 1-4; FTHLICC 2003a, pp. 2-3; Piest and Knowels 2006, pp. 1-4). These documents have, to a greater or lesser extent, estimated the areal extent of current and historical flat-tailed horned lizard habitat in all or certain portions of its range. One of the more detailed of such analyses was Hodges (1997, pp. 15-16), who concluded that 503,161 ha (1,243,341 ac) out of 979,016 ha (2,419,200 ac), or about 51 percent, of flat-tailed horned lizard habitat in the United States had been destroyed by past development.

However, such calculations, no matter how carefully crafted, are necessarily based on assumptions of what areas constituted historical habitat for the species (such as Hodges 1997, p. 10). Because much of the area within the range of the flat-tailed horned lizard was converted to agricultural and urban development during the early half of the 20th century (

see

Background section, above) prior to any systematic surveys for the flat-tailed horned lizard, little reliable information exists on the historical distribution of the species (Barrows

et al.

2008, p. 1886).

We questioned the validity of such assumptions in our past assessments. For example, Hodges (1997, pp. 5, 7, and 16) included the area now inundated by Salton Sea as historical habitat, but we stated in our 2003 withdrawal that the Salton Sea area could arguably be considered ephemeral historical habitat. In our 2006 withdrawal, we concluded that the former lakebed of historical Lake Cahuilla (including and beyond the present-day Salton Sea) likely was not habitat important to the flat-tailed horned lizard (71 FR 36750-36751). The information on the genetics of flat-tailed horned lizard populations raises further doubts about the validity of the assumptions made in earlier assessments, both by us and by others, of historical flat-tailed horned lizard habitat.

As discussed above (

see

Background section), genetic data readily support three of the four geographic populations as distinct, indicating that these populations generally had little genetic interchange among each other (Mulcahy

et al.

2006, pp. 1807-1826; Culver and Dee 2008, pp. 1-14). This lack of genetic exchange suggests a barrier separated, and likely still separates, these populations. As discussed in the Background section, the areas within the present-day Imperial Valley, Mexicali Valley, and San Luis Valley were historically interlaced by a network of Colorado River-influenced water courses, including the Alamo River, the New River, and the Río Hardy (or their precursors or equivalents). Historically, these “rivers” were dependent upon the Colorado River for water and only transported water periodically. Prior to the increase of agricultural development and prior to the digging of the irrigation canal and subsequent flood that created the Salton Sea early in the 20th century (

see

Background section), some areas along these river channels were characterized by Parish (1914, p. 88) as having “channels, sloughs, and lagoons.” These hydrologically influenced areas likely did not contain flat-tailed horned lizard habitat, as defined in the Background section. As such, not all of the area between the present-day Salton Sea and the Gulf of California, including areas outside the lakebed of historical Lake Cahuilla, historically supported flat-tailed horned lizard habitat. This information further supports our conclusion presented in our 2006 withdrawal that the “area of the historical range periodically inundated by Lake Cahuilla was not important to the long-term viability of the flat-tailed horned lizard because this area was frequently unavailable and likely contained little quality habitat” (71 FR 36750).

Because of the extensive manmade changes to the landscape, we cannot precisely determine with any degree of specificity how much of the area was historically flat-tailed horned lizard habitat. Moreover, we maintain that much uncertainty exists with any attempt to precisely quantify the amount of flat-tailed horned lizard habitat that has been destroyed by historical agricultural development, as has been attempted in the past. We agree with the conclusions of previous assessments, both by us and by others, that portions of the Coachella, Imperial, Mexicali, Yuma, and San Luis Valleys once provided suitable areas of flat-tailed horned lizard habitat. We also agree that historical agricultural development (and, to a lesser extent, urban development) destroyed large areas with flat-tailed horned lizard habitat, thus curtailing the size of the Coachella Valley, Western, Eastern, and Southeastern flat-tailed horned lizard populations in both the United States and Mexico. However, the effects of past actions are better addressed under Factor E.

In the sections below, we address the present or threatened destruction, modification, or curtailment of the habitat or range of the flat-tailed horned lizard. We evaluate the current and anticipated effects associated with several types of land development, the invasion of nonnative plants, OHV activity, and military training. We first describe the respective threats in general terms and then assess those threats to the habitat or range of the flat-tailed horned lizard, focusing on subareas (such as identified populations or Management Areas) within the species' range, where appropriate.

Development

We define development as commercial and residential development (

i.e.,

urban development), and the conversion of land for any agricultural purpose. Such development not only includes the obvious associated infrastructure (e.g., roads, pipelines, canals, and power lines), but also reservoirs, power generation facilities, and resource extraction operations such as drilling and mining.

For the purpose of evaluating the threats to a species and its habitat, we focus on the developmental activities that threaten to convert land from a natural or undeveloped state to land no longer suitable as habitat for the species. We consider both the direct and, where appropriate (within the context of Factor A), the indirect effects of such developmental activities. While land development typically has a similar effect, that is the destruction or modification of habitat, differing land uses resulting from development activities can lead to different indirect effects. We therefore distinguish among the types of development when evaluating the effects of such development on a species or its habitat.

For this evaluation of flat-tailed horned lizard under Factor A, we determine whether development is a current or anticipated threat to flat-

tailed horned lizard habitat. Below, we address agricultural and urban development, as well as development associated with energy generation projects.

Agricultural Development

Within the dry Colorado Desert, agricultural activity is substantially dependent upon irrigation water imported from the Colorado River. As discussed in the Background section, most of the agricultural development within the range of the flat-tailed horned lizard occurred early in the 20th century. Because Colorado River water is a finite resource, agricultural development is no longer expanding into new areas and destroying flat-tailed horned lizard habitat to any substantial degree. Information available from the Coachella Valley Water District (CVWD 2002, p. 1; 2003, p. 1; 2004, p. 1; 2005, p. 25; 2006, p. 27; 2007, p. 25; 2008, p. 25; 2009, p. 25) indicates a slight decline in the amount of irrigable acres and a fairly steady though variable amount of water delivered from 2001 to 2008, indicating that new agricultural development has not occurred in the Coachella Valley within the past decade or so. Also, fields are being fallowed in the Imperial Valley because less water is available for irrigation in this area (IID 2006, p. 1). Thus, conversion of land for agriculture is no longer considered a threat to flat-tailed horned lizard habitat in the Coachella Valley and in the Imperial Valley portions of the Western and Eastern Populations, and is not considered to be a threat in the foreseeable future.

In contrast, recent agricultural development has destroyed flat-tailed horned lizard habitat in other areas. Between 2002 and 2006, an unreported but minority fraction of 1,534 ha (3,790 ac) of flat-tailed horned lizard habitat was developed for agricultural use in Arizona (Piest and Knowles 2006, p. 1). Rodriguez (2002, p. 21) also recorded recent agricultural development in Mexico; however, the majority of the agricultural development in the Mexicali and San Luis Valleys occurred in the early to mid-20th century, closely following the historical agricultural development north of the border (Furnish and Ladman 1975, pp. 84-88). Additionally, about 60 percent of the flat-tailed horned lizard habitat in Mexico lies within two Mexican Federal natural protected areas, the Upper Gulf of California and Colorado Delta Biosphere Reserve (la Reserva de la Biosfera del Alto Golfo de California y Delta del Río Colorado), and the Pinacate and Gran Desierto de Altar Biosphere Reserve (la Reserva de la Biosfera El Pinacate y Gran Desierto de Altar) (CEDO 2001, p. 3), where agricultural development is limited by Mexican law.

Agricultural activities outside of the areas receiving Colorado River water are severely restricted by the climate of the Salton Trough region, including in Mexico. Thus, while recent agricultural development destroyed areas of flat-tailed horned lizard habitat in the Southeastern Population, the overall acreages were small, especially compared to the amount of habitat available in the Southeastern Population.

Agricultural development, most of which occurred between 1945 and the 1980s (Mills 2009, p. 28), occurred in the Borrego Springs area of the habitat occupied by the Western Population. The Borrego Springs area uses a local aquifer for irrigation, and the area does not receive Colorado River water; however, the aquifer is overdrawn (County of San Diego 2008, p. 8; Mills 2009, p. 4). We do not anticipate substantial amounts of agriculture to expand into adjoining natural lands in this area (see Mills 2009, pp. 40-42). Moreover, the area of private lands in the Borrego Valley is constrained within Anza-Borrego Desert State Park. As a result, we believe that agricultural development no longer threatens flat-tailed horned lizard habitat in the Borrego Springs portion of the Western Population, nor will it in the foreseeable future.

In conclusion, the available information indicates that the vast majority of the agricultural development within the range of the flat-tailed horned lizard took place in the historical past and only a small amount of development has been documented in recent times. Because conversion of land to agriculture in the region is limited by the availability of irrigation water and that water is limited, we do not expect agriculture to expand significantly into adjoining flat-tailed horned lizard habitat in the future. Moreover, increased demand for water outside the region has resulted in a decreased amount of Colorado River water available for agriculture in the Imperial Valley, which has resulted in the fallowing of fields in this area. Therefore, we conclude that agricultural development is not a substantial threat to the flat-tailed horned lizard throughout its range, nor is it anticipated to be in the foreseeable future.

Urban Development

Like agricultural development, urban development largely occurred in the historic past. Many of the urban centers in the region that serve agricultural communities are contained within agricultural areas. While urbanization has continued as the human population within the region has grown (FTHLICC 2003a, p. 12; Indrelunas 2010, pp. 1-3), most of this urban development associated with these urban centers has come at the expense of former croplands. As such, this development is not currently destroying substantial amounts of available flat-tailed horned lizard habitat (FTHLICC 2003a, p. 12). However, certain areas of urban development not associated with active or past agriculture have resulted in the destruction of flat-tailed horned lizard habitat. This impact is most evident in the Coachella Valley where urban development not associated with agricultural communities continues today (Indrelunas 2010, pp. 1-3). This growth is corroborated by the number of domestic water meter services, which grew by over 25 percent from 2001 to 2008 (CVWD 2002, p. 1; 2003, p. 1; 2004, p. 1; 2005, p. 25; 2006, p. 27; 2007, p. 25; 2008, p. 25; 2009, p. 25). This urban growth is occurring in the surrounding desert areas, which likely include flat-tailed horned lizard habitat. Our interpretation of past and recent aerial imagery supports this trend.

The flat-tailed horned lizard now appears to be restricted to two occurrences within the Coachella Valley MSHCP plan area, the Thousand Palms conservation area and the Dos Palmas conservation area (CVCC 2010, p. 13). The Coachella Valley MSHCP includes numerous measures to minimize and mitigate impacts of urban development on the flat-tailed horned lizard (see Coachella Valley Multiple Species Habitat Conservation Plan (Coachella Valley MSHCP) section above for a detailed discussion). Approximately 94 percent of the potential habitat where flat-tailed horned lizards are known to occur in the Thousand Palms conservation area is land that is already protected (Table 2), including about 62 percent that is part of the Coachella Valley National Wildlife Refuge. Similarly, approximately 34 percent of the habitat at Dos Palmas is protected (Table 2). The high level of protection of flat-tailed horned lizard habitat at the Thousand Palms conservation area translates into a low magnitude of threat from urban development at this location. In contrast, because only about one-third of the flat-tailed horned lizard habitat at the Dos Palmas conservation area is currently in protected status, the potential magnitude of urban development at the latter location is

greater. However, because this area of habitat is farther away from existing urban areas, the immediacy of the threat of urban development is likely lower, even without the protections for flat-tailed horned lizard included in the Coachella Valley MSHCP plan (which requires the protection of the Dos Palmas conservation area). Therefore, the overall threat from urban development of flat-tailed horned lizard habitat in the Coachella Valley Population is low.

Most of the area occupied by the U.S. portion of the Western Population of flat-tailed horned lizards is owned by the State of California (more than 27 percent) or by the Federal government (more than 52 percent), and the vast majority of the U.S. portion of the Eastern Population is federally owned (more than 95 percent). Much of the State of California land in the Western Population is administered by California State Parks, including Anza-Borrego Desert State Park and Ocotillo Wells State Vehicular Recreation Area. We do not expect any substantive urban development activities on State Park-administered lands. However, such development, should it occur, would likely follow the avoidance, minimization, and compensation measures of the Rangewide Management Strategy because California State Parks is a signatory agency to the Interagency Conservation Agreement.

Additionally, much of the Federal land is administered by the BLM, which is a signatory to the Interagency Conservation Agreement. Moreover, the BLM has incorporated the Rangewide Management Strategy into the California Desert Conservation Area (CDCA) Plan under the Federal Land Policy and Management Act of 1976 (43 U.S.C. 1701

et seq.

) (FLPMA). The CDCA Plan directs BLM's permitting of development projects on the lands the plan covers, including the U.S. portions of the Western and Eastern Populations. Thus, the avoidance, minimization, and compensation measures in the Rangewide Management Strategy are implemented by BLM on these lands, which reduces the impact such development to flat-tailed horned lizard habitat. Other federally owned lands in these areas are lands owned by the Navy, which is also a signatory to the Interagency Conservation Agreement. Not only do we anticipate that the Navy's participation in the Rangewide Management Strategy will continue, which will limit the amount of impact to flat-tailed horned lizard habitat, but the Navy's use of these lands, largely as bombing ranges, will result in little urban development on these lands. As such, we expect the amount of impact from urban development on areas of flat-tailed horned lizard habitat owned by the State of California and the Federal government in the Western and Eastern Population to be small now and within the foreseeable future because little urban development is likely on State Park lands and most military lands, and what development that may occur on Federal lands will be minimized through implementation of the Rangewide Management Strategy, including through implementation of the CDCA Plan on BLM lands.

Moreover, the designation of the Borrego Badlands, West Mesa, and Yuha Desert Management Areas offer protective mechanisms for 96,599 ha (238,700 ac) (Table 1) of flat-tailed horned lizard habitat within this population. Impacts from permittee actions are limited to 1 percent of the area within Management Areas (FTHLICC 2003a, p. 33). As described above, we expect minimal or no urban development on Federal and California State lands within the area occupied by the Western Population and Eastern Population, but urban development may occur within private lands. Although private inholdings are scattered throughout the Federal and State lands in the region, few concentrations of private land exist. The largest concentration of private inholdings within the areas occupied by the Western Population occurs in and around the community of Borrego Springs, California. Urban development in this area is limited to a finite area within the Borrego Springs area, which is an area of private lands completely surrounded by Anza-Borrego Desert State Park. Additionally, development in this area may be further restricted by a limitation in the amount of available groundwater (Mills 2009, p. 4). As we concluded in 2003 (68 FR 342), even if urban development continues, this area is small enough that it is unlikely that the combined urban or agricultural development in or around this geographically limited area poses a significant threat to the flat-tailed horned lizard throughout its range. Moreover, limited water and isolation of the remaining private lands scattered within the public lands likely will prevent any large-scale urban development in the region, further reducing the effects that urbanization may have on the Western Population of the flat-tailed horned lizard. Because the Mexican portion of the Western Population is isolated from other inhabited areas by the Sierra de Los Cucapahs and the dry lakebed of Laguna Salada, we believe urban development in this area is likely similarly limited by available resources and isolation. Thus, we conclude that urban development is not a threat to the species in the Western Population, nor is it likely to become a threat in the foreseeable future.

As discussed above, we expect impacts from urban development on Federal lands in the Eastern Population to be limited. Moreover, the designation of the East Mesa Management Area offers protective mechanisms for 45,248 ha (111,810 ac) (Table 1), or about 27 percent of the Eastern Population, of flat-tailed horned lizard habitat within this population. Impacts from permittee actions are limited to 1 percent of the area within each Management Area (FTHLICC 2003a, p. 33). Additionally, 10,654 ha (26,327 ac), or about 6 percent of the Eastern Population, is designated as a Wilderness Area where urban development is prohibited. Most urban development occurs on private property, and less than 5 percent of the U.S. portion of the Eastern Population area occurs on private property. Limited water and isolation of the private lands likely prevent any substantive urban development in the region, including the small amount of habitat in Mexico. Thus, we conclude that urban development is not a threat to the species in the Eastern Population, nor is it likely to become a threat in the foreseeable future.

Urban development has occurred recently in the Southeastern Population of flat-tailed horned lizards. Areas of recent urbanization include development near the communities of Yuma, Arizona (Piest and Knowles 2006, p. 1); San Luis Río Colorado, Sonora, Mexico (Rodriguez 2002, p. 23); and Puerto Peñasco, Sonora, Mexico (Rodriguez 2002, p. 23). Most (about 84 percent) of the flat-tailed horned lizard habitat in Arizona is federally owned, where urban development is less likely, and most of the U.S. Federal land in the Southeastern Population is within the 53,014-ha (131,000-ac) Yuma Desert Management Area (Table 1), where impacts from permittee actions are limited to 1 percent of the area (FTHLICC 2003a, p. 26). Additionally, avoidance and minimization measures are in place within the Barry M. Goldwater Range, Arizona, to prevent or limit impact to the flat-tailed horned lizard and its habitat from military development (USFWS 1996, pp. 18 and 58). Nevertheless, development impacts may occur. For example, construction by Marine Corps Airs Station, Yuma, of a new aircraft landing field and associated infrastructure for the F-35B

Joint Strike Fighter at the Barry M. Goldwater Range is expected to permanently remove 33.5 ha (82.7 ac) of flat-tailed horned lizard habitat, plus have additional long-term adverse effects on a 17.8 ha (44 ac) (USFWS 2010b, p. 46). Even so, this project includes minimization measures called for by Rangewide Management Strategy, thereby reducing the impact of this development to the species and its habitat (USFWS 2010b, pp. 10-12, 45). Thus, we conclude that urban development in Arizona is not a significant threat to the species, nor is it likely to become a threat in the foreseeable future.

In Mexico, urban development is likely within the foreseeable future around San Luis Río Colorado, Puerto Peñasco, and elsewhere along the Gulf of California coast. Despite an increase in accessibility to remote areas (Búrquez and Martínez-Yrízar 1997, p. 390), the vast majority of the habitat for the Southeastern Population in Mexico remains isolated with respect to urban development, because urban development requires access to other resources, which are not necessarily available with mere physical access. Moreover, compared to the 1,005,630 ha (2,484,966 ac) of flat-tailed horned lizard habitat in the Mexican portion of the Southeastern Population, roughly 60 percent of which lies within two Mexican Federal natural protected areas where development is limited (CEDO 2001, p. 3), we expect the amount of urban development to be relatively small. Thus, we conclude that urban development is not a significant threat to the species in the Mexican portion of the Southeastern Population, nor is it likely to become a threat in the foreseeable future.

Therefore, despite some urban development occurring in the Southeastern Population, we believe that this development is small relative to the overall amount of flat-tailed horned lizard habitat in the Southeastern Population and is unlikely to significantly increase in the foreseeable future; thus, this development does not pose a substantial threat to the species in the Southeastern Population, nor is it likely to become a threat in the foreseeable future.

In conclusion, flat-tailed horned lizard habitat has been lost to urban development in the Coachella Valley, and we expect urbanization to continue there. The available information indicates the distribution of the species in the Coachella Valley is now limited to two occurrences that are within two Coachella Valley MSHCP conservation areas (CVCC 2010, p. 8); although nearly all of the flat-tailed horned lizard habitat in the Thousand Palms reserve is already protected, most of the Dos Palmas reserve is not (see Table 2). Implementation of the Coachella Valley MSHCP is expected to limit the impacts to the flat-tailed horned lizard and its habitat (USFWS 2008, Appendix A, p. 317). Furthermore, in our evaluation of the potential impacts of the plan's implementation on the flat-tailed horned lizard (USFWS 2008, p. 178), we concluded: “After reviewing the current status of this species, environmental baseline for the action area, effects of the proposed action, and cumulative effects, it is the Service's biological opinion that the action, as proposed, is not likely to jeopardize the continued existence of the flat-tailed horned lizard. Loss of the Coachella Valley population would have a negligible [effect] on the status of the species as a whole, since it makes up approximately 1 percent of the current range of the flat-tailed horned lizard. Persistence of the species in the Plan area is likely only with effective Plan implementation.” Because of the limited amount of private land, urban development is also only likely to destroy relatively small amounts of flat-tailed horned lizard habitat in the Western, Southeastern, and Eastern Populations. Additionally, in areas of flat-tailed horned lizard habitat in the United States and Mexico where urbanization has the potential to occur, it is likely that the amount of urban development will be limited by the availability of water and the isolated nature of many of these areas. The implementation of the Rangewide Management Strategy further restricts development in the United States, limiting impacts inside designated flat-tailed horned lizard Management Areas to 1 percent of the area. In Mexico, urban development is likely to be limited within the Federal natural protected areas (Rodriguez 2002, p. 25). Therefore, we conclude that urban development is not a significant threat to flat-tailed horned lizard habitat throughout its range, nor is it anticipated to become a significant threat in the foreseeable future.

Energy Generation Facility Development

The analyses in the 1993 proposed rule and 2003 withdrawal document both identified development of geothermal energy facilities as a potential threat to flat-tailed horned lizard habitat. Since then, increased interest in renewable forms of electrical generation has resulted in a greater number of proposed energy development facilities and their associated infrastructure. Recent proposals not only include geothermal facilities, but also projects harnessing solar radiation and wind. Examples of recent proposals that may affect flat-tailed horned lizard habitat include the following: geothermal projects near the Superstition Mountains (Navy 2008, pp. 1-40) and the Truckhaven area west of Salton City (BLM 2007a, pp. 1-3), solar projects near Plaster City (BLM and CEC 2010, p. ES-1), and a wind project west of the community of Ocotillo (Ocotillo Express 2009, p. 1). Because the development of energy generation facilities occurs within the range of the flat-tailed horned lizard habitat, we assess the magnitude of this development to the species below.

Similar to other forms of development, energy generation projects may result in destruction or modification of flat-tailed horned lizard habitat. These projects can include buildings, roads, power lines, and pipelines, although they differ in the details. For example, geothermal plants typically include wells and pipelines (often aboveground), solar plants typically include solar collecting arrays (using various technologies to convert solar energy to electrical energy), and wind farms have lines or arrays of wind turbines.

The total acreage of potential development for renewable energy facilities is small compared to the overall range of the species. For example, in California, the BLM maintains a GIS database of rights-of-way applications for energy generation facilities. Additional permits are needed before the potential facilities listed in the database can be built, and even if they obtain all of the necessary permits, it is not guaranteed that all of them will be built. Moreover, some of these right-of-way applications have been rejected, denied, or withdrawn. However, assuming that the facilities in the BLM database are built, the total area of development on BLM land for all of the applications on file as of December 2010 would be about 2,585 ha (6,387 ac) in the Eastern Population, and 18,841 ha (46,556 ac) in the Western Population. The BLM data only include areas of BLM (Federal) land and do not include what, if any, nearby private land that may also be developed as part of these energy projects. We do not have data for the potential impacts to private lands adjacent to these areas, but we made a rough assessment of the adjacent private land that may potentially be included in these projects which may add about 260 ha (about 640 ac) to the impacts in the Eastern Population and about 10,600 ha (about 26,000 ac) to the impacts in the Western Population. Using these values,

the energy development in the Eastern Population may impact roughly 2,845 ha (7,030 ac) of BLM and private lands, which is about 1.7 percent of the Eastern Population area, and the energy development in the Western Population may impact roughly 29,441 ha (72,750 ac) of BLM and private lands, which is about 8.6 percent of the Western Population area. Combined, these projects—assuming that they are all built, which is not likely—would impact a total of about 2 percent of the nearly 1.6 million ha (3.9 million ac) of the total range of the species (using 2003 “current distribution”).

Although we expect additional energy development facilities may be constructed elsewhere within the range of the species, including in Arizona and Mexico, we are not aware of any specific proposals that are as large as those proposed in California. Therefore, we conclude that the total acreage of potential development for renewable energy facilities is small compared to the overall range of the species. Additionally, on lands managed by signatory agencies to the Interagency Conservation Agreement, we expect the impacts to flat-tailed horned lizard habitat (whether inside or outside of designated Management Areas) will be further reduced because of the avoidance, minimization, and compensation measures of the Rangewide Management Strategy.

Moreover, because of the avoidance and minimization measures, including the 1-percent impact limit in flat-tailed horned lizard Management Areas, most of the energy generation facilities have been proposed outside of the Management Areas, although some impacts to Management Areas are anticipated resulting from related infrastructure development (FTHLICC/MOG 2010, p. 2). For example, the 2,454-ha (6,063-ac) Imperial Valley Solar project site is proposed outside of the flat-tailed horned lizard Management Areas called for by the Rangewide Management Strategy, but an associated transmission line is expected to run for about 12 kilometers (km) (7.5 miles (mi)) within the Yuha Desert Management Area. However, this proposed transmission line was routed along an existing powerline corridor to minimize effects to flat-tailed horned lizard habitat in the Management Area (BLM and CEC 2010, pp. B.1-18, C.2-9, and C.2-42).

While project sites may be proposed within flat-tailed horned lizard Management Areas, the Rangewide Management Strategy limits the total acreage of impacts for a given Management Area to no more than 1 percent. As of 2009, signatory agencies control approximately 196,273 ha (485,000 ac) of flat-tailed horned lizard habitat in the designated Management Areas and have collectively permitted activities on 171.57 ha (423.97 ac), or 0.09 percent (Table 1). Thus far, signatory agencies have consistently implemented the Rangewide Management Strategy, even in permitting development electrical generation facilities. Moreover, the implementation of the Rangewide Management Strategy is not completely voluntary at this point; aspects of the Rangewide Management Strategy have been incorporated into documents that implement regulatory mechanisms, including the Federal Land Policy and Management Act (43 U.S.C.1701

et seq.

) (FLPMA), which affects development on BLM lands (

see

Factor D). Many of the anticipated energy development facilities are on BLM lands or otherwise would require easements or access across BLM lands; thus, the development of these energy generation facilities would be subject to the provisions of the Rangewide Management Strategy through implementation of FLPMA.

In sum, the overall acreage of potential impacts from development of energy facilities is likely to be small compared to the total range of the species, including private lands likely to be developed. Moreover, because of the prevalence of Federal and State lands in the U.S. portions of the range of the flat-tailed horned lizard and because most of this land is managed by signatories to the Interagency Conservation Agreement implementing the Rangewide Management Strategy, we expect that the vast majority of proposed energy development projects that are likely to affect flat-tailed horned lizard habitat in the United States will be subject to the avoidance, minimization, and compensation measures incorporated into the Rangewide Management Strategy, including in areas outside of designated Management Areas. The signatories to the Interagency Conservation Agreement have been actively implementing the Rangewide Management Strategy since its inception, and have committed to its continued implementation. Additionally, the Rangewide Management Strategy has been incorporated into the CDCA Plan, which means it will be implemented as a regulatory mechanism (as opposed to a voluntary agreement). Although the Rangewide Management Strategy is not in effect in Mexico, the amount of habitat that is likely to be destroyed by energy development projects in that country is likely to be small relative to the total amount of habitat. Therefore, we anticipate the development of energy generation facilities does not now nor in the foreseeable future pose a significant threat to flat-tailed horned lizard and its habitat.

Invasive, Nonnative Plants

In our 2003 withdrawal document, we included the effects of invasive, nonnative plants as a potential threat to flat-tailed horned lizard habitat (68 FR 345). However, we concluded that nonnative plants did not pose a substantial threat because of the limited extent to which such plants had established themselves in flat-tailed horned lizard habitat (68 FR 345). The available literature also suggests invasive, nonnative plants are a potential threat to flat-tailed horned lizard habitat (such as Hodges 1997, pp. 4, 5, and 9; CEDO 2001, p. 2; FTHLICC 2003a, pp. 18-19; Hammerson

et al.

2007, p. 4), but specifics on how nonnative species are impacting flat-tailed horned lizard habitat are generally lacking.

The perennial nonnative tree,

Tamarix aphylla

(athel pine), has been planted as a windbreak in the Coachella Valley. This tree can reduce or prevent wind-transport of sand, thereby reducing available flat-tailed horned lizard habitat there (England 1983, p. 152). Although

T. aphylla

typically spreads vegetatively by adventitious roots or submerged stems, the species can spread sexually by seed following flood events (Walker

et al.

2006, pp. 191-201). While perhaps not as invasive as other species of

Tamari

x (Cal-IPC 2003, p. 4),

T. aphylla

trees have been removed in some Coachella Valley MSHCP reserve areas in the Coachella Valley as management to improve habitat (FTHLICC 1999, p. 4). Moreover, the population of flat-tailed horned lizards in the Coachella Valley proper is now found only in the Thousand Palms reserve area (CVCC 2010, p. 8), where the plan's habitat management is focused. Therefore, we do not consider

T. aphylla

to be an invasive, nonnative species that is threatening flat-tailed horned lizard habitat.

Nonnative annual plants, such as

Brassica tournefortii

(Saharan mustard),

Schismus barbatus

(common Mediterranean grass), and

Salsola kali

(Russian thistle), can blanket certain areas of the Colorado Desert in years with higher amounts of rainfall (Brown and Minnich 1986, pp. 411-422; Lovich and Bainbridge 1999, p. 318; FTHLICC 2003a, p. 18; Yurkowsky 2005,

in litt.,

Anza-Borrego Desert State Park; Barrows

et al.

2009, pp. 673-686). Such nonnative plants may adversely affect flat-tailed horned lizard habitat throughout its range by altering fire regimes (Brown and Minnich 1986, pp. 418-421; Brooks and Esque 2002, pp. 334-336); stabilizing Aeolian soils (i.e., soil that is transported from one place to another by wind; Barrows

et al.

2009, p. 684); changing plant assemblages (Barrows

et al.

2009, p. 683); and changing the availability of seeds for harvester ants, the primary food source for the flat-tailed horned lizard (Gordon 1980, p. 70). Dense stands of plants, which are typical of invasive, nonnative plant species in years of higher amounts of rainfall, also may challenge the locomotor abilities of the wide-bodied flat-tailed horned lizard (Newbold 2005, p. 17).

Plant growth will vary annually in the Colorado Desert because of the variable amount and timing of rainfall that the region receives. Moreover, annual plants die by the end of spring, and in the harsh desert climate the amount of standing biomass of the annual plants, once dead, quickly decreases (Barrows

et al.

2009, p. 684). We expect the amount and timing of rainfall within the range of the species will continue to be variable into the foreseeable future, even with the potential effects of climate change (Field

et al.

1999, pp. 8-10). As a result, the effects of invasive, nonnative plants are generally short-lived in areas of flat-tailed horned lizard habitat (Barrows

et al.

2009, p. 673), and because of the likelihood of continued variability in precipitation, we expect the potential effects of invasive, nonnative plants to continue to be short-lived into the foreseeable future. With the potential exception of increased occurrence of wildland fires, we do not believe that the growth of invasive, nonnative plants poses a lasting, significant threat to flat-tailed horned lizard habitat now or in the foreseeable future. We examine the potential threat of wildland fire below.

Fires typically are rare events in the western Sonoran Desert because of the natural “limited biomass, wide spacing between shrubs and sparse ground cover” (Brown and Minnich 1986, p. 411). However, the periodic increase in the amount of available fuel from nonnative, annual plants in years of heavy precipitation has allowed the frequency, size, and intensity of fires in desert plant communities to increase (Brown and Minnich 1986, p. 411; Brooks and Berry 2006, pp. 117-118; Trader

et al.

2006, p. 314; see also Rorabaugh 2010, p. 191). Moreover, many of the native perennial plants within the range of the flat-tailed horned lizard typically take a long time to recover after a fire (O'Leary and Minnich 1981, pp. 61-66; Brown and Minnich 1986, p. 411; Brooks and Esque 2002, p. 330). Thus, fire can change the species composition of the perennial and annual plant communities. Moreover, provided enough water (rainfall) is available, annual plants, especially nonnative species, proliferate after a fire (Minnich 1994, p. 104), which may provide additional fuel and promote additional wildfires. Plant communities in areas with recurrent fires may convert from vegetation types dominated by native shrubs into types dominated by nonnative annual grasses and forbs (type conversion) (Brown and Minnich 1986, p. 411). Type conversion appears to be occurring near the highly urbanized areas, such as the Coachella Valley (Brown and Minnich 1986, p. 411), where increased human activity offers higher numbers of ignition sources (Brooks and Esque 2002, p. 337), but not in the more remote areas of flat-tailed horned lizard habitat. Moreover, the amount of rainfall is a critical factor in how much plant growth occurs (Barrows

et al.

2009, p. 673). The amount of rainfall is unpredictable within the range of the flat-tailed horned lizard, and is likely to be so for the foreseeable future. It is not clear how the fire regime will be affected long term, but in the foreseeable future, wildland fire does not appear to be a threat.

Additionally, it is unclear whether this localized change in vegetation affects the specific habitat components upon which flat-tailed horned lizards rely. For example, flat-tailed horned lizards take refuge under perennial shrubs for shade and to avoid predators (Muth and Fisher 1992, pp. 1-77; Sherbrooke 2002, pp. 109-120). Fire typically kills the existing desert shrubs, but shrubs do regrow after a fire, although the plant species composition is likely to have changed (Brown and Minnich 1986, pp. 411). Thus, during the period of time following fire while shrubs are regrowing, flat-tailed horned lizards will have fewer options for thermoregulation and predator avoidance. While this condition is not permanent, it remains unclear if the change in plant species composition will have a lasting effect on the flat-tailed horned lizard, especially if type conversion were to occur. Nonetheless, because this change in plant species composition is localized, we conclude any potential effects are low in magnitude at the species level, likely temporary, and thus not a significant threat to the species.

Another potential threat to the flat-tailed horned lizard that may arise from a change in plant species composition after a fire is that harvester ants, the primary food of the flat-tailed horned lizard, could be affected. Fire likely kills individual harvester ants on the surface at the time of the fire, but evidence suggests the underground colonies survive (Zimmer and Parmenter 1998, p. 282; Underwood and Christian 2009, p. 325). As described in the Background section, harvester ants eat seeds of annual and perennial plant species. Although changes in plant composition may alter the type and quantities of available seeds consumed by ants, ant forage likely will not be eliminated, and may even increase because of the increase in annual plants (Zimmer and Parmenter 1998, p. 282; Underwood and Christian 2009, p. 325). For example, several of the species found by Gordon (1980, p. 72) to be important to harvester ants were also species of plants found by Brown and Minnich (1986, p. 416) to do well after a fire. Therefore, wildland fire does not appear to pose a threat to harvester ants.

In conclusion, the spread of invasive, nonnative plants does not appear to be a significant threat to flat-tailed horned lizard habitat throughout its range at this time, nor is it likely to become a significant threat in the foreseeable future.

Off-Highway Vehicles (OHVs)

The analyses in the 1993 proposed rule and 2003 withdrawal document included OHV activity as a potential threat to the flat-tailed horned lizard. The Rangewide Management Strategy also describes off-highway (OHV) or off-road vehicle activity as a potential threat (FTHLICC 2003a, pp. 12-14). We consider OHVs to be all vehicles used off-road, including, but not limited to, automobiles, dune buggies, motorcycles, all-terrain-cycles, four-wheelers, and military vehicles. OHV activity includes, but is not limited to, recreational, military, law-enforcement (such as Border Patrol), and trans-border trafficking activities. As discussed in the Background section, flat-tailed horned lizard habitat typically consists of sandy flats and valleys occupied by plant species that are typical of the creosote-white bursage plant association. The presence of ants as a food source is also important.

OHV activity may modify flat-tailed horned lizard habitat because of impacts to vegetation (Luckenbach 1975, p. 4; Vollmer

et al.

1976, p. 115; Bury

et al.

1977, p. 7; Lathrop 1983, p. 164; Luckenbach and Bury 1983, p. 280; Groom

et al.

2007, p. 133), soil

disturbance (Luckenbach 1975, p. 4;, Bury

et al.

1977, pp. 16-18;, Webb 1983, pp. 51-79), and introduction of nonnative plants (Brooks and Lair 2005, p. 8). Additionally, some but not all areas with high OHV activity have been shown to have fewer harvester ant colonies (McGrann

et al.

2006, p. 77).

Past studies of OHV impacts on lizards (Busack and Bury 1974, p. 182; Bury

et al.

1977, p. 10; Luckenbach and Bury 1983, p. 273; Klinger

et al.

1990, pp. 1-17; Beauchamp

et al.

1998, p. 214; Gardner 2002, p. 14; Wright and Grant 2003, p. 30) have been largely inconclusive or cannot be readily applied across the range of the flat-tailed horned lizard (that is, they have limited “inference space” (Ratti and Garton 1994, pp. 1-23)). Luckenbach and Bury (1983, p. 278) reported that a pronounced reduction in flat-tailed horned lizard abundance around the Algodones Dunes had been anecdotally noted by scientists. Marked declines in herbaceous and perennial plants, arthropods, lizards, and mammals in OHV-used areas compared with nearby control areas were also reported by Luckenbach and Bury (1983, p. 265). The declines, however, were for the Colorado Desert fringe-toed lizard (

Uma notata

) and beetles, and did not include flat-tailed horned lizards or ants. Additionally, research has been conducted in creosote-dominated habitats in the Mojave Desert. Researchers compared reptile metrics (measures) between sites used differentially by OHVs and control sites (Bury

et al.

1977, pp. 1-23). Bury

et al.

(1977, p. 11) found a significant decrease in numbers of reptiles on OHV-used areas compared to numbers on control sites in the Mojave Desert. However, the highest number of desert horned lizards on any one plot occurred on a moderately used OHV site (Bury

et al.

1977, p. 10). In research conducted by both Busack and Bury (1974, p. 182) and Bury

et al.

(1977, p. 1), there appeared to be an inverse relationship between increased use of OHVs and the abundance of lizards; this means that, as OHV use increased, lizard abundance decreased. Additionally, McGrann

et al.

(2006, pp. 77-79) found that the density of flat-tailed horned lizards was lower in areas of high OHV activity, as was the average body mass of individual flat-tailed horned lizards, suggesting the habitat quality—including harvester ant abundance—in some high-use OHV areas was not as good; however, the authors also noted that small sample size may have allowed qualitative differences between sites sampled to affect their results.

Research in the Ocotillo Wells SVRA found flat-tailed horned lizards at higher densities in non-sandy habitats than sandy habitats within the SVRA, which differed from most other research findings (Beauchamp

et al.

1998, pp. 213-214). However, it was unclear if flat-tailed horned lizards were found in these atypical habitat types because they are more variable in habitat use than previously thought, because these habitat types are more available in the Ocotillo Wells SVRA than other areas in which flat-tailed horned lizards have been studied, or as a response to OHV activity (Beauchamp

et al.

1998, p. 214).

OHV activity occurs in the Western, Eastern, and Southeastern Populations, but the amount (intensity, frequency) of OHV activity varies across the landscape, with greater amounts of activity in areas designated for OHV use and areas near existing roads, and lesser amounts in areas where OHV use is not permitted or areas that are away from easy access. In the Coachella Valley, OHV activity is expected to be controlled in protected habitat areas through implementation of the Coachella Valley MSHCP (CVAG 2007, pp. 9-117) and OHV activity is not identified as a conservation issue in the annual report for 2009 (CVCC 2010, p. 14). In our evaluation of the potential impacts of the plan's implementation on the flat-tailed horned lizard (USFWS 2008, p. 178), we concluded: “After reviewing the current status of this species, environmental baseline for the action area, effects of the proposed action, and cumulative effects, it is the Service's biological opinion that the action, as proposed, is not likely to jeopardize the continued existence of the flat-tailed horned lizard. Loss of the Coachella Valley population would have a negligible [effect] on the status of the species as a whole, since it makes up approximately 1 percent of the current range of the flat-tailed horned lizard. Persistence of the species in the Plan area is likely only with effective Plan implementation.” Additionally, approximately 94 percent of the potential habitat where flat-tailed horned lizards are known to occur in the Thousand Palms conservation area is land that is already protected (Table 2), including about 62 percent that is part of the Coachella Valley National Wildlife Refuge.

OHV activity along the United States-Mexico international boundary (border) was identified as a potential threat to the flat-tailed horned lizard and its habitat (FTHLICC 2003a, p. 12). The amount of impact to flat-tailed horned lizard habitat along the border is not clear. To put the potential impact in context of the range of the species, we assumed an area of high impact from border-related OHV activity to be within a 1-km (0.6-mi)-wide zone north of the border. We estimate that the total area of flat-tailed horned lizard habitat within that “zone” is about 12,662 ha (31,288 ac), or about 0.8 percent of the range of the species, comprising 2,318 ha (5,728 ac), 5,012 ha (12,385 ac), and 5,332 ha (13,176 ac) of the Western, Eastern, and Southeastern Populations, or about 0.7 percent, 3 percent, and 0.5 percent of those populations, respectively. This zone of assumed high activity is a broad-brush assessment (for example, the All-American Canal runs along the border in the Eastern Population, likely confining any border-related OHV activities in certain areas to less than 1 km (0.6 mi)). Nevertheless, the zone is small compared to the range of the species and the three populations, individually. Moreover, since 2008, the U.S. Customs and Border Protection constructed the “border fence,” which is a vehicle and, in some areas, pedestrian barrier, plus associated infrastructure, in certain areas between the United States and Mexico. Although some areas of the border are not fenced, the areas of flat-tailed horned lizard habitat along the border are fenced (USCBP 2008a, p. 1-5; USCBP 2008b, p. 2-4; Rorabaugh 2010, p. 181). Prior to construction of the border fence, the new fence and associated infrastructure was anticipated to result in reduction of the amount of illegal, cross-border traffic (USCBP 2008b, p. 3-18). Additionally, as part of the installation of the border fence, a stabilized patrol road on the U.S. side was constructed. The use of the road was also expected to result in an overall decrease in ground disturbance because Border Patrol agents would patrol from vehicles on the road rather than through OHV activity (USCBP 2008a, p. 2-7). Indeed, evidence suggests the border fence has reduced illegal cross-border traffic and associated OHV activity (Rorabaugh 2010, p. 190), thereby reducing the amount of potential impact to flat-tailed horned lizard habitat along the border from illegal trans-border OHV activity and subsequent law-enforcement OHV activity by the Border Patrol.

Moreover, the scientific literature is mixed and inconclusive with respect to the impact of OHV activity on the flat-tailed horned lizard and its habitat. Setser and Young (2000, p. 11) and Setser (2001, p. 12) found flat-tailed horned lizards avoided areas disturbed by OHVs. However, there was no difference in flat-tailed horned lizard habitat use between areas within 10 m

(33 ft) of OHV trails and sites farther away from OHV trails (Setser and Young 2000, p. 11; Setser 2001, p. 12). Setser and Young (2000, p. 11) and Setser (2001, p. 12) concluded that: (1) OHV use might render sites less suitable to flat-tailed horned lizard use, because of the impacts of OHV activity on vegetation and soil characteristics; or (2) OHV trails occur on sites not preferred by flat-tailed horned lizards (e.g., barren ground with no plants or rocks). However, Gardner (2002) and Setser (2004, p. 54) suggested that OHV activity did not have an effect on flat-tailed horned lizards at different areas in the Ocotillo Wells SVRA, on the basis of observations.

In summary, while there has been some research on the adverse effects of OHV activity on vegetation, soils, and flat-tailed horned lizards, its applicability to flat-tailed horned lizard populations is limited and unreliable because of the lack of scientific rigor associated with the research designs. Additionally, the effects of OHV activity on flat-tailed horned lizard populations were not the primary research questions. Nevertheless, these studies have utility in generating hypotheses concerning variation in degree of OHV use and flat-tailed horned lizard abundance. At this time, we conclude that the available studies do not collectively show that OHV activity causes declines in flat-tailed horned lizard populations throughout the range of the species or that adverse OHV impacts pose a significant threat to flat-tailed horned lizard habitat. Management activities, including efforts to reduce conflicts with actions that impact flat-tailed horned lizard habitats, would be enhanced by focused research. Impacts of OHV activity on flat-tailed horned lizard populations should be studied using rigorous research designs to yield conclusions with high degrees of certainty (Ratti and Garton 1994, pp. 1-23) regarding the effects of OHV activity on flat-tailed horned lizard populations across the range of the species. In conclusion, OHV activity does not appear to be a significant threat to flat-tailed horned lizard habitat throughout its range at this time, nor is it likely to become a significant threat in the foreseeable future.

Military Training Activities

The Rangewide Management Strategy (FTHLICC 2003a, p.15) summarizes military activity within the range of the flat-tailed horned lizard. The species occurs on two military installations: (1) The western Barry M. Goldwater Range, administered by Marine Corps Air Station (MCAS) Yuma, and (2) Naval Air Facility (NAF) El Centro. MCAS Yuma manages approximately 46,458 ha (114,800 ac) within the 53,014-ha (131,000-ac) Yuma Desert Management Area, while NAF El Centro manages approximately 12,060 ha (29,800 ac) within the 55,078-ha (136,100-ac) West Mesa Management Area and 3,440 ha (8,500 ac) in the 46,660-ha (115,300-ac) East Mesa Management Area. The U.S. Marine Corps and U.S. Navy are signatories to the Interagency Conservation Agreement implementing the Rangewide Management Strategy.

The training ranges are primarily used for aircraft-related training. Activities that have the potential to impact flat-tailed horned lizard habitat include non-exploding bombing practice, ground-based training, target maintenance, clean up of target sites, road maintenance, mobile target activity, and target and run-in-line grading. Most military activities are confined to previously disturbed areas, so the amount of destruction or modification of flat-tailed horned lizard habitat is limited (FTHLICC 2003a, p.15). Additionally, the military is committed to be good stewards of lands they control, and the two installations have incorporated measures to benefit the flat-tailed horned lizard and other wildlife resources into their planning, training, and management activities (Navy 2001, chapter 3; USAF and USMC 2007, p. 1-8 and chapter 5). Therefore, we do not anticipate military training activities to substantially affect flat-tailed horned lizard habitat now or in the foreseeable future.

Summary of Factor A Threats

Flat-tailed horned lizard habitat could potentially be impacted by urban or agricultural development. However, due to the remote location and increasingly limited availability of water, urbanization and agricultural conversion of flat-tailed horned lizard habitat will likely be limited in the United States and Mexico over the foreseeable future. We note that development of energy facilities is increasing, especially in the southwestern United States; however, the overall acreage of impact from these projects, assuming all of the proposed right-of-way applications are constructed, is small compared to the range of the species. In the United States, we expect development impacts to occur outside of the existing Management Areas due to avoidance and minimization measures that result from implementation of the Rangewide Management Strategy. As of 2009, signatory agencies control approximately 185,653 ha (458,757 ac), or about 40 percent of flat-tailed horned lizard habitat in the United States, within the Management Areas, of which only 0.09 percent has been permitted for impacts. Furthermore, in the United States, most of the species' habitat is federally or State (such as California State Park) owned, where impacts to habitat from development are anticipated to be minimal. In Mexico, the amount of development that may occur in flat-tailed horned lizard habitat is small relative to the large amount of habitat that is available, and thus the effects to the species are expected to be low in magnitude. Therefore, current or anticipated future urban, agricultural, or energy development throughout the species' range is not currently a substantial threat to the flat-tailed horned lizard, nor do we expect it to become a substantial threat in the foreseeable future.

Invasive, nonnative plants could increase the potential for wildland fire in a desert environment where wildland fire is naturally infrequent. Research suggests that invasive, nonnative plant conversion of flat-tailed horned lizard habitat is limited to urbanized and adjacent areas, and is not a substantive threat to the species' habitat throughout its range. Also, frequent OHV activity has the potential to affect flat-tailed horned lizard habitat; however, the available studies do not collectively show that OHV activity causes declines in flat-tailed horned lizard populations throughout the range of the species or that adverse OHV impacts pose a significant threat to flat-tailed horned lizard habitat. Lastly, military training activities have limited impacts on the ground and are not expected to substantially affect flat-tailed horned lizard habitat. We do not consider the potential threats analyzed above to be substantial threats to the flat-tailed horned lizard, either individually or in combination. Therefore, based on our review of the best available scientific and commercial information, we find the flat-tailed horned lizard is not threatened by the present or threatened destruction, modification, or curtailment of its habitat or range, either now or in the foreseeable future.

B. Overutilization for Commercial, Recreational, Scientific, or Educational Purposes

Within the context of this listing factor, overutilization is the capture or collection of individuals of a species to an extent (at a high enough rate) to affect the status of the species. Historically, in the United States, flat-tailed horned lizards may have been among the species of horned lizard

collected for the curio trade (Bolster and Nicol 1989, pp. 2 and 7). Flat-tailed horned lizard were identified by Stewart (1971, p. 33) as utilized in the pet trade. This species was also collected for scientific and educational purposes (Bolster and Nicol 1989, p. 9). However, the collection of the flat-tailed horned lizard is now prohibited except by permit in California (California Administrative Code 40.10, Title 14) and Arizona (Arizona Game and Fish Regulation, Title 17, R12-4-443, Commission Order 43). The flat-tailed horned lizard is also listed in the Official Mexican Norm NOM-059-ECOL-2001, Mexico's threatened species law, as a threatened species in Mexico (SEMARNAT 2002, p. 134), and collection is prohibited without a permit. Because of the difficulty in locating these cryptically colored lizards, we expect unauthorized recreational collection to be rare. In Mexico, Hammerson

et al.

(2007, p. 5) noted that the species may be utilized in the pet trade. As noted in Rodriguez (2002, p. 26), some people in Mexico have flat-tailed horned lizards in their yards, but it is unclear whether those lizards are prevented from moving out. We have no information on the magnitude of the pet trade, but horned lizards in general are known to be difficult to keep alive as captive pets (Stewart 1971, p. 34), including in Mexico (Rodriguez 2002, p. 26). This suggests that the pet trade is small. The information we have, although limited, does not suggest that the amount of utilization that has occurred recently, regardless of purpose, has significantly affected the status of the flat-tailed horned lizard. Therefore, based on our review of the best scientific and commercial information, we find that overutilization for any purpose is not a threat to the flat-tailed horned lizard, now or in the foreseeable future.

C. Disease or Predation

Disease occurs to some extent in nearly all wildlife populations, but it is only a threat if the disease is virulent to the extent that it significantly impacts the population. We are not aware of any reports of disease in flat-tailed horned lizards. Thus, we do not consider disease to be a threat to the flat-tailed horned lizard anywhere within its range, nor is there any evidence to suggest it is likely to become a threat in the foreseeable future.

Predation occurs naturally, and nearly all populations of wildlife species are subject to some level of predation. Predation of flat-tailed horned lizards is known to occur. For example, 16 of 42 radio-tagged flat-tailed horned lizards were depredated in a 2-year study (Muth and Fisher 1992, p. 33), although the rate of predation they observed may have been affected by the presence of the radio tags themselves by making the otherwise cryptically colored lizard more apparent to predators. For predation to be a significant threat to the flat-tailed horned lizard, predation rates must be high enough to affect the status of the species such that mortality from predation outpaces births resulting in an overall population decline. Predation has been identified as a potential threat to the flat-tailed horned lizard (FTHLICC 2003a, pp. 16-17). A summary from multiple sources in the scientific literature is presented in the Rangewide Management Strategy (FTHLICC 2003a, p. 16), which identifies known or likely predators to be six species of birds, five species of reptiles, two species of mammals, and one arthropod. Of these, the round-tailed ground squirrel (S

permophilus tereticaudus

) and the loggerhead shrike (

Lanius ludovicianus

) were highlighted as major predators (FTHLICC 2003a, p. 16; see also Young and Young 2000, p. 60; Young

et al.

2004a, p. 65). Most of these predators occur naturally (including historically) in areas occupied by flat-tailed horned lizards; thus, predation is not a threat that has emerged recently.

However, information from the scientific literature suggests that the populations of some of these predators are now higher as a result of manmade changes to the landscape, resulting in increased predation of flat-tailed horned lizards in these areas (FTHLICC 2003a, pp. 16-17; Young and Young 2005, p. 8). For example, Barrows

et al.

(2006, pp. 492-493) found evidence suggesting that loggerhead shrikes and other avian predators were responsible for reduced populations of flat-tailed horned lizards near wildland-urban interface, and Young and Young (2005, p. 8) suspected round-tailed ground squirrel populations are similarly augmented with manmade changes to landscape, resulting in similar declines in flat-tailed horned lizard populations in and around urban areas. Additionally, the cryptic coloration that allows flat-tailed horned lizards to blend in with desert soils may be of little use on paved roads, allowing increased levels of predation (Young and Young 2000, p. 62). However, much of the range of the flat-tailed horned lizard is remote, away from areas of manmade change. Thus, for the flat-tailed horned lizard, predation does not appear to be excessively high throughout its range but instead localized near developed areas. This suggests that the observed high level of predation of flat-tailed horned lizards is an “edge effect” associated with the interface between natural areas and areas of urban and agricultural development. Because the proportion of developed areas within the range of the species is small in comparison to the undeveloped areas, we do not consider increased predation associated with urbanization to be a significant threat to the species. We further consider predation as a secondary effect of development, which is discussed under Factor E, below.

Summary of Factor C Threats

Disease does not appear to be a threat at this time, nor is it likely to become a significant threat in the foreseeable future. Predation likely occurs in some human-altered areas at higher than typical rates; however, compared to the distribution of the species, relatively few flat-tailed horned lizards are likely subjected to increased predation. Therefore based on our review of the best scientific and commercial information, we find the flat-tailed horned lizard is not threatened by disease or predation, now or in the foreseeable future.

D. The Inadequacy of Existing Regulatory Mechanisms

In the 1993 proposed rule to list the species, we identified several State (Arizona and California), U.S. Federal, and Mexican Federal laws and other existing regulatory mechanisms that could provide benefits to the flat-tailed horned lizard (58 FR 62627), and we concluded that these regulatory mechanisms were inadequate to protect the species or its habitat (58 FR 62628). In 1997, we also noted several State (Arizona and California), U.S. Federal, and Mexican Federal laws, but particularly noted the benefits provided to the flat-tailed horned lizard by the Interagency Conservation Agreement implementing the Rangewide Management Strategy (62 FR 37858-37859). In 2003, we again noted several State (Arizona and California), U.S. Federal, and Mexican Federal laws and other existing regulatory mechanisms that could provide benefits to the flat-tailed horned lizard (68 FR 346).

Because the Interagency Conservation Agreement implementing the Rangewide Management Strategy is voluntarily implemented on the part of the signatories, we do not consider it to be a regulatory mechanism per se. Some entities have incorporated the Interagency Conservation Agreement into other regulatory mechanisms; in such cases, the Interagency

Conservation Agreement is mentioned in the context of those regulatory mechanisms. Additionally, two habitat conservation plans (HCPs) within the range of the flat-tailed horned lizard cover the species and provide mitigation for and conservation of habitat. While implementation of these HCPs will provide localized benefits to the flat-tailed horned lizards populations within the HCP boundaries, these HCPs cover a very small portion of the flat-tailed horned lizard's range and will not substantially influence the overall status of the species. The Interagency Conservation Agreement and the two HCPs are discussed in greater detail in the Background section above.

In the preceding analyses of the threats to the flat-tailed horned lizard under Factors A, B, and C, and in our analysis of threats under Factor E, below, all of the threats presented are of low magnitude, are non-imminent, and/or cover very small portions of the species' range. In the sections that follow, we first discuss the existing regulatory mechanism(s) that would be removed as a result of the withdrawal of the proposed rule to list the species. Then we review the existing regulatory mechanisms that would remain in effect to address the potential threats discussed herein under the other listing factors.

U.S. Federal Laws

Section 7(a)(4) of the Act

The Act contains provisions for Federal agencies to confer with the Secretary on any action that is likely to jeopardize the continued existence of any species proposed to be listed under the Act. Commonly called a “conference,” this requirement would no longer apply to the flat-tailed horned lizard once the withdrawal of the proposed listing rule is finalized. A conference opinion is an advisory mechanism by which the Service recommends measures to avoid adverse effects or jeopardy to the species. There are no requirements to implement reasonable and prudent measures and terms and conditions or for adoption of reasonable and prudent alternatives to avoid impacts to species or habitat. In this regard, the conference opinion requirement under the Act provides little if any additional regulatory protection for this species; although it may provide some benefits to the flat-tailed horned lizard by informing Federal agencies of poten

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