Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Cactus Ferruginous Pygmy-Owl as Threatened or Endangered With Critical Habitat
Federal RegisterOct 5, 2011
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
[FWS-R2-ES-2011-0086; MO 92210-0-0008]
Endangered and Threatened Wildlife and Plants; 12-Month Finding on a Petition To List the Cactus Ferruginous Pygmy-Owl as Threatened or Endangered With Critical Habitat
AGENCY:
Fish and Wildlife Service, Interior.
ACTION:
Notice of 12-month petition finding.
SUMMARY:
We, the U.S. Fish and Wildlife Service (Service), announce a 12-month finding on a petition to list the cactus ferruginous pygmy-owl (
Glaucidium brasilianum cactorum
) as threatened or endangered and to designate critical habitat under the Endangered Species Act of 1973, as amended (Act). Additionally, the petition requested that we recognize and list a western subspecies of the cactus ferruginous pygmy-owl (
Glaucidium ridgwayi cactorum
), or, alternatively, two potential distinct population segment (DPS) configurations. After review of all available scientific and commercial information, we find that
Glaucidium ridgwayi cactorum
is not a valid taxon, and, therefore, not a listable entity under the Act. Additionally, using the currently accepted taxonomic classification of the pygmy-owl (
Glaucidium brasilianum cactorum
), we find that listing the pygmy-owl is not warranted at this time throughout all or a significant portion of its range, including the petitioned and other potential DPS configurations. However, we ask the public to submit to us at any time any new information concerning the taxonomy or status of the pygmy-owl, as well as any new information on the threats to the pygmy-owl or its habitat.
DATES:
The finding announced in this document was made on October 5, 2011.
ADDRESSES:
This finding is available on the Internet at
http://www.regulations.gov
at Docket Number FWS-R2-ES-2011-0086. Supporting documentation we used in preparing this finding is available for public inspection, by appointment, during normal business hours at the U.S. Fish and Wildlife Service, Arizona Ecological Services Office, 2321 West Royal Palm Road, Suite 103, Phoenix, AZ 85021-4951. Please submit any new information, materials, comments, or questions regarding this finding to the above address.
FOR FURTHER INFORMATION CONTACT:
Steve Spangle, Field Supervisor, Arizona Ecological Services Office (see
ADDRESSES
); telephone 602-242-0210; or by facsimile 602-242-2513. If you use a telecommunications device for the deaf (TDD), please call the Federal Information Relay Service (FIRS) at 800-877-8339.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act (Act) (16 U.S.C. 1531
et seq.
) requires that, for any petition to revise the Federal Lists of Endangered and Threatened Wildlife and Plants that contains substantial scientific and commercial information that listing a species may be warranted, we make a finding within 12 months of the date of receipt of the petition. In this finding, we determine whether the petitioned action is: (1) Not warranted, (2) warranted, or (3) warranted, but immediate proposal of a regulation implementing the petitioned action is precluded by other pending proposals to determine whether species are threatened or endangered, and expeditious progress is being made to add or remove qualified species from the Lists of Endangered and Threatened Wildlife and Plants. Section 4(b)(3)(C) of the Act requires that we treat a petition for which the requested action is found to be warranted but precluded as though resubmitted annually on the date of such finding. Therefore, a new finding is to be made within 12 months and subsequently thereafter until we take action on a proposal to list or withdraw our original finding. We must publish these 12-month findings in the
Federal Register.
Previous Federal Actions
On March 20, 2007, we received a petition dated March 15, 2007, from the Center for Biological Diversity and Defenders of Wildlife (petitioners) requesting that we list the cactus ferruginous pygmy-owl (
Glaucidium brasilianum cactorum
) (pygmy-owl) as a threatened or endangered species under the Endangered Species Act (Act) (CBD and DOW 2007). Additionally, the petition requested the designation of critical habitat concurrent with listing. The petition clearly identified itself as a petition and included the identification information, as required in 50 CFR 424.14(a). We acknowledged the receipt of the petition in a letter to the petitioners dated June 25, 2007, stating that we were proceeding with a review of the petition.
The petitioners described three potentially listable entities of the pygmy-owl: (1) An Arizona distinct population segment (DPS) of the pygmy-owl; (2) a Sonoran Desert DPS of the pygmy-owl; and (3) the western subspecies of the pygmy-owl, which they identified as
Glaucidium ridgwayi cactorum.
As an immediate action, the petitioners requested that we promulgate an emergency listing rule for the pygmy-owl. In our June 25, 2007, response letter to the petitioners, we described our evaluation of the need for emergency listing and stated our determination that emergency listing was not warranted for the pygmy-owl. We also stated that the designation of critical habitat would be considered if listing of the pygmy-owl was found to be warranted.
In the
Federal Register
of June 2, 2008 (73 FR 31418), we published a 90-day finding in which we determined that the petition presented substantial scientific and commercial information to indicate that listing the pygmy-owl may be warranted. A more thorough summary of previous Federal actions related to the pygmy-owl can be found in the June 2, 2008 90-day finding (73 FR 31418).
Following the publication of our 90-day finding on this petition, we initiated a status review to determine if listing of the pygmy-owl was warranted. During our status review, we solicited and received information from the general public and other interested parties on the status of the pygmy-owl. We consulted with experts, agencies, countries, and tribes to gather pertinent information, and ensure that experts and affected parties were aware of the status review and of the opportunity to provide input. We identified, contacted, and consulted with a diverse group of experts and interested persons in an effort to ensure that we gathered and evaluated the best available scientific and commercial information on this subspecies to inform our 12-month finding.
On December 12, 2009, we received a 60-day Notice of Intent to Sue from the petitioners for failure to produce a timely 12-month finding on their petition. They subsequently filed suit on February 17, 2010, in the U.S. District Court for the District of Arizona. That complaint was subsequently consolidated in the U.S. District Court for the District of Columbia along with another case filed by the Center for Biological Diversity and thirteen cases filed by Wild Earth Guardians, all related to petition finding deadlines. The court in the consolidated case
approved two settlement agreements between the parties on September 9, 2011.
In re Endangered Species Act Deadline Litigation,
Misc. Action No. 10-377 (EGS), MDL Docket No. 2165 (D.D.C. Sept. 9, 2011) (Docs. 55 & 56). The settlement agreements stipulate that the Service will submit to the Federal Register a proposed listing rule or a not warranted finding for the cactus ferruginous pygmy-owl no later than the end of Fiscal Year 2011, which is September 30, 2011.
This notice constitutes a 12-month finding for the petition to list the pygmy-owl as threatened or endangered. We base our finding on a review of the best scientific and commercial information available, including all substantive information received during our status review.
In this finding, we first provide background information on the biology of the pygmy-owl. Included in this background is our analysis of the petitioner's request that we recognize a western subspecies of the pygmy-owl (
Glaucidum ridgwayi cactorum
), which represents a proposed change in the taxonomic classification of the pygmy-owl. Then, we consider each of the five factors listed in section 4(a)(1) of the Act. For each factor, we first determine whether any negative impacts appear to be affecting the pygmy-owl anywhere in the subspecies' range, and whether any of these impacts rise to the level of threats such that the pygmy-owl is endangered or threatened throughout its range, according to the statutory standard.
After the rangewide assessment, we evaluate the validity of the petitioned distinct population segments (DPSs), as well as other potential DPS configurations suggested by information submitted during the status review or by the ecology, occurrence, and distribution of the pygmy-owl. This analysis determines whether any of the DPS configurations meet the criteria for discreteness and significance under our DPS policy (see Distinct Vertebrate Population Segment section below). We then evaluate whether there is a significant portion of the pygmy-owl's range that warrants further evaluation, consistent with the Act's definitions for “endangered species” and “threatened species,” which requires analysis of whether a “species” is endangered or threatened within “a significant portion of its range” (see Significant Portion of the Range section below). Finally, we make our finding with regard to the petitioned action and our evaluation as described above.
Species Information
Description
The pygmy-owl is in the order Strigiformes and the family Strigidae. It is a small bird, approximately 17 centimeters (cm) (6.75 inches (in)) long. Generally, male pygmy-owls average 58 grams (g) to 66 g (2.0 to 2.3 ounces (oz)) and females average 70 g to 75 g (2.4 to 2.6 oz) (AGFD 2008b, p. 3; Proudfoot and Johnson 2000, p. 16; Johnsgard 1988, p. 159). The pygmy-owl is reddish brown overall, with a cream-colored belly streaked with reddish brown. Color may vary, with some individuals being more grayish brown (Proudfoot and Johnson 2000, pp. 15-16). The crown is lightly streaked, and a pair of dark brown or black spots outlined in white occurs on the nape, suggesting “eyes,” leading to the name “Cuatro Ojos” (four eyes), as it is sometimes called in Mexico (Oberholser 1974, p. 451). The species lacks ear tufts, and the eyes are yellow. The tail is relatively long for an owl and is reddish brown in color, with darker brown bars. Pygmy-owls have large feet and talons relative to their body size.
Taxonomy
The petitioners requested that we recognize a change in the taxonomic classification of the pygmy-owl (CBD and DOW 2007, pp. 1-2). In considering taxonomic data, the Service relies “on standard taxonomic distinctions and the biological expertise of the Department and the scientific community concerning the relevant taxonomic group” (50 CFR 424.11(a)) and on “the best available scientific and commercial information” (50 CFR 424.11(b)). The use of specific taxonomic data is at the discretion of the Service, as long as the information is reliable and meets the above standards. With regard to the pygmy-owl, existing avian checklists attempt to present the most current taxonomic classifications, but discrepancies among checklists demonstrate that there is scientific debate and disagreement over some accepted taxonomic designations. Taxonomic changes within these checklists generally occur as a result of a proposal to change the existing taxonomy. Lack of reference to a proposed taxonomic change within these checklists cannot be interpreted as rejection (or acceptance) of a proposed change. It may simply mean a proposal has not been submitted or evaluated. Absolute reliance on one or more of these avian checklists, absent consideration of recent studies, would be arbitrary on the part of the Service. The Service has the responsibility for deciding what taxonomic entities are to be protected under the Act, based on the best available scientific information. We address any conflicting information or conflicting expert opinion by carefully evaluating the underlying scientific information and weighing its reliability and adequacy according to the considerations of the Act and our associated policies and procedures.
When we previously listed the pygmy-owl as endangered in 1997 (62 FR 10730; March 10, 1997), and in all subsequent regulatory and legal actions, we followed the currently accepted taxonomic classification,
Glaucidium brasilianum cactorum.
We considered
G. b. cactorum
to occur from lowland central Arizona south through western Mexico to the Mexican states of Colima and Michoacán, and from southern Texas south through the Mexican states of Tamaulipas and Nuevo Leon, consistent with most of the contemporary literature (Johnsgard 1988, p. 159; Millsap and Johnson 1988, p. 137; Oberholser 1974, p. 452; Friedmann
et al.
1950, p. 145), and the last American Ornithologist Union (AOU) list that addressed avian classification to the subspecies level (AOU 1957) (Figure 1). The AOU checklist is generally accepted as the primary authority for avian taxonomic classification, and the 1957 AOU checklist description is the currently accepted taxonomic classification of the pygmy-owl at the subspecies level.
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The petitioners requested a revised taxonomic consideration for the pygmy-owl based on Proudfoot
et al.
(2006a, p. 9; 2006b, p. 946) and König
et al.
(1999, pp. 160, 370-373), classifying the northern portion of
Glaucidium brasilianum'
s range as an entirely separate species,
G. ridgwayi,
and recognizing two subspecies of
G. ridgwayi
—
G. r. cactorum
in western Mexico and Arizona and
G. r. ridgwayi
in eastern Mexico and Texas (Figure 1). Other recent studies proposing or supporting the change to
G. ridgwayi
for the northern portion of
G. brasilianum's
range have been published in the past 15 years (Heidrich
et al.
1995, p. 2, 25; Navarro-Siguenza and Peterson 2004, p. 5).
Groups classified within species, such as subspecies, are important in the discussion of biodiversity because they represent the evolutionary potential within a species. Recognizing this, a number of existing lists of threatened, endangered, or special status species include subspecific groups (Haig
et al.
2006, p. 1585). We considered the information in these existing lists and other literature as we evaluated the petitioned taxonomic classification. The 1957 AOU checklist is the last AOU checklist that described subspecies. Subsequent AOU checklists have limited their descriptions to the species level only and are, therefore, not helpful in our evaluation.
In our 90-day finding for this petition (73 FR 31418), we indicated that the petition presented reliable and substantive information that a taxonomic revision may be warranted. The suggested taxonomic change is based on recently published recommendations (Proudfoot
et al.
2006a, p. 9; 2006b, p. 946; König
et al.
1999, pp. 160, 370-373) to revise pygmy-owl taxonomy. Various other publications also provide evidence that the taxonomic status of the pygmy-owl has not been resolved (Proudfoot and Johnson 2000, pp. 4-5; König
et al.
1999, p. 373; Phillips 1966, p. 93; Buchanan 1964, p. 107). Information received during our status review also indicates that pygmy-owl taxonomy needs additional work to resolve current questions (Johnson and Carothers 2008b, pp. 5-6; Robbins 2008, p. 1; Voelker 2008, p. 1).
Taxonomic nomenclature for the pygmy-owl has changed over time. Originally called
Glaucidium ferrugineum
in 1872 by Coues (Coues 1872, p. 370), the pygmy-owl has also been known as
G. ferrugineus
(Aiken 1937, p. 29) and
G. phalo(a)enoides
(Fisher 1893, p. 199; Gilman 1909, p. 115, Swarth 1914, p. 31; Kimball 1921, p. 57). Since the 1920's, the pygmy-owl has been classified as
G. brasilianum
(van Rossem 1937, p. 27; Bent 1938, p. 435; Peters 1940, p. 130; Brandt 1951, p. 653; Sutton 1951, p. 168). We will focus our discussion at the subspecies level since the petitioned entity is at the subspecies level of classification. As such, we will not evaluate or discuss whether the appropriate species classification is
G. brasilianum
or
G. ridgwayi.
The petitioners asked the Service to recognize a subspecies,
Glaucidium ridgwayi cactorum,
described by
Proudfoot
et al.
(2006a, pp. 9-10; 2006b, p. 2, 9) as the listable entity in the petition. The primary difference between the petitioned subspecies and the currently accepted description of
G. brasilianum cactorum
is the latter's more extensive distribution to the south and east (Figure 1). The range of the
G. b. cactorum
subspecies we originally listed in 1997 is Arizona, northwestern Mexico, the Lower Rio Grande Valley of Texas, and northeastern Mexico, for a general distribution that runs from central Mexico northward on both sides of the Sierra Madre mountains into Arizona and Texas. The range of the proposed
G. r. cactorum
does not extend as far south as
G. b. cactorum.
The two
G. ridgwayi
subspecies proposed by the petition encompass the northwestern (
G. r. cactorum
) and northeastern (
G. r. ridgwayi
) extensions of the range of
G. b. cactorum.
Specifically, the petition describes the range of the suggested subspecies,
G. r. cactorum,
as extending from Arizona on the north through the States of Sonora and Sinaloa in Mexico (Figure 2).
EP05OC11.004
Our analysis of whether to accept the petitioners' proposed
Glaucidium ridgwayi cactorum
subspecies as a listable entity includes an evaluation of whether there are historical or current descriptions or studies of the proposed subspecies that would support the description of the petitioned subspecies based on Proudfoot
et al.
(2006a, 2006b). A number of subspecies of
G. brasilianum
have been described or suggested (Proudfoot and Johnson 2000, p. 4; Friedmann
et al.
1950, pp. 145-147), including various descriptions of a
cactorum
subspecies, the distribution of some of which generally match the petitioned subspecies. Therefore, the delineation of a
cactorum
subspecies as petitioned is not a new classification, but one that has been described previously in the literature under
G. brasilianum.
With regard to existing literature, van Rossem (1937, pp. 27-28) described the earliest
cactorum
subspecies that approximates the distribution of the petitioned subspecies. This was a newly described subspecies of ferruginous pygmy-owl and was described from a “giant cactus grove between Empalme and Guaymas * * * Sonora, Mexico” (van Rossem 1937, p. 27). Van Rossem restricted this new subspecies to northwestern Mexico and Arizona (Figure 3). Van Rossem also included a more southern and eastern subspecies,
ridgwayi,
that was described as occurring in southern Mexico and central America, but also Texas (van Rossem, 1937, pp. 27-28). He specifically excluded the Texas population from
cactorum,
about which
he wrote “they approximate very closely the measurements and tail characters of
cactorum
* * * in color they are best referred to
ridgwayi”
(van Rossem 1937, pp. 27-28; italics added). The 1944 AOU checklist accepted this classification and described its distribution as southern Arizona to Nayarit, in western Mexico (AOU 1944, p. 50) (Fig. 3). However, in a later publication van Rossem (1945, p. 111) indicated that
cactorum
extended only to the Sonora and Sinaloa border in Mexico (Figure 3), perhaps excluding Nayarit, because his 1937 publication indicates that the specimen from Nayarit was not typical (van Rossem 1937, p. 28). Karalus and Eckert (1971, p. 223) give a southern distribution for
cactorum
of western and northwestern Sonora (Figure 3). Proudfoot
et al.
(2006a, p. 9; 2006b, p. 7) indicate the state of Sinaloa is the southern extent of the range, while König
et al.
(1999, p. 373) extend the distribution of
cactorum
into Nayarit and Jalisco in western Mexico (Figure 3). Freethy (1992, p. 121) simply states that western Mexico is the southern limit of
cactorum.
Clements (2007, p. 171) recognizes the
cactorum
subspecies, but gives no distribution.
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The chronology described in the previous paragraph, which excludes the currently accepted distribution of
Glaucidium brasilianum cactorum,
focuses on descriptions in the literature which generally approximate the petitioned description of
G. ridgwayi cactorum,
and there is consensus that
cactorum
extended northward into Arizona. However, it is evident there is inconsistency regarding the southern extent of the subspecies. With the exception of van Rossem (1937, pp. 27-28), who uses morphological characteristics to describe the subspecies, most of the above descriptions of the
cactorum
subspecies do not indicate why they have ascribed the subspecies to the ranges indicated in these publications. König
et al.
(1999, p. 373) simply uses the morphological characters of van Rossem (1937, pp. 27-28). König
et al.
(1999, entire) and Proudfoot
et al.
(2006a; 2006b, entire) do classify
cactorum
using genetic data, but draw different conclusions with regard to the southern boundary. The incremental southward extension of the various
cactorum
ranges may provide some support for the idea of a clinal pattern of differentiation in which genetic and morphological differences occur in an incremental manner, as opposed to more abrupt changes that are more likely to represent a boundary between two distinct subspecies groupings. The data presented in the petition (Proudfoot
et al.
2006a; 2006b, entire) are not sufficient to clarify the groupings in the literature, nor does it allow us to determine if the subspecies ranges are distinct because there is a lack of adequate sampling in southern and eastern Mexico. The uncertainty of the southern boundary would suggest that additional sampling is needed to refine this portion of the range of
cactorum.
In the presence of unresolved inconsistencies, the Service relies upon the “standard taxonomic distinctions (50 CFR 424.11(a)); in this case, the currently accepted taxonomic classification (AOU 1957).
In addition to reviewing historical and current descriptions of the subspecies, we requested review and input on the issue of taxonomic classification of the petitioned entity from 10 individuals with biological expertise and background in this issue. Of the 10 we consulted, 5 provided comments on specific questions we asked regarding the issues of taxonomic classification, genetic differentiation, and genetic diversity based on recent and historical studies and publications related to pygmy-owl taxonomic classification. Information submitted by all five experts indicated that, while there are certain aspects of the information presented in the petition that support acceptance of the petitioned entity, there is insufficient information regarding how to define a distinct subspecies. Additional work is needed to clarify the distribution of the subspecies, especially in regards to the southern boundary (Voelker 2008, p. 1; Cicero 2008, p. 2; Robbins 2008, p. 1; Oyler-McCance 2008, pp. 1-2; Dumbacher 2008, pp. 2-8). A summary of their comments is presented below.
Dumbacher (2008, p. 7) provided a summary of considerations in response to our request for input on this issue: “In summary, Proudfoot
et al.
2006a and 2006b do not provide a critical test for the subspecies
Glaucidium ridgwayi ridgwayi
or
G.r. cactorum
or their geographical ranges. The data are consistent with current subspecies names in that they show: (1) Isolation by distance across the range, albeit with larger genetic breaks in the region that corresponds with the subspecies names [as described by van Rossem 1937]; (2) and significant variation among major geographical areas that broadly correspond to present subspecies names [van Rossem 1937]. However, it is not clear: (1) Where exactly the subspecies boundaries occur; (2) whether the boundary will be geographically distinct or correspond to characters used in the original subspecies designation, such that the two groups would qualify for subspecies under the 75 percent rule [75 percent of individuals in a new subspecies (or region) are diagnosably different from the other possible subspecies]; or (3) whether a broad hybrid zone or cline would be discovered that might call the two subspecies into question. Further data are needed to critically test the validity of the subspecies and to identify the most appropriate geographic boundary between them. Proudfoot
et al.
(2006b) make a plea for more data in critical areas, such as between Sonora and Sinaloa, and I would argue further south as well.”
Cicero (2008, p. 2) adds, “On the basis of these data, I would argue that Arizona and Texas populations should be managed as separate units. However, further study of the variation in morphology and plumage (the characters originally used to describe
cactorum
) is needed before we can reliably apply names to these populations. Thus, in my opinion, the molecular data provided by Proudfoot
et al.
(2006a and 2006b) do not clarify subspecific limits and ranges in North American populations of
G. brasilianum”.
Similarly, Oyler-McCance (2008, p. 2) indicates that, “within the United States, it is clear that the Arizona group is much different from the Texas group and should not be considered as one group. What is less clear, however, is where exactly to draw the boundary between the two subspecies * * *. It would be informative to look at other characteristics (morphology, behavior, geographic distribution) and see how well they fit with the patterns provided by the genetic data. Only then, using all those characteristics, would it be prudent to make a decision.”
Robbins (2008, p. 1) indicated that work on a molecular-based phylogeny of New World pygmy-owls is about to be completed that will inform this issue. He suggested that acceptance of the petitioned entity be delayed until this work has been published. However, the study to which Robbins refers will focus on species-level analyses, and it may not provide additional information regarding the distribution of subspecies and, as of the date of this finding, has not yet been published.
Recently, the Committee on Classification and Nomenclature on North and Middle American birds (the Checklist Committee) of the AOU considered a proposal to separate
Glaucidium brasilianum ridgwayi
as a distinct species, but rejected that proposal, citing the need to wait for additional work (AOU 2009).
In fairness to Proudfoot and his collaborators, their two 2006 studies are more general in nature and did not have the objective of defining pygmy-owl classification to the subspecies level. In addition, Proudfoot and his fellow authors, similar to the authors of many other publications related to pygmy-owl taxonomy, pointed out the need for additional work to clarify the taxonomic classification of pygmy-owls. Therefore, when we consider the recent information provided by Proudfoot
et al.
(2006a; 2006b, entire) and König
et al.
(1999, entire), in combination with the historical descriptions of distributions for the subspecies
cactorum,
there is evidence of a general nature that the petitioned subspecies may have merit. However, after reviewing the best available information, we find that uncertainty and inconsistency exists with regard to the delineation of the range of these subspecies.
The peer reviewers who provided information to the Service regarding this issue represent respected experts with considerable knowledge of the current science regarding avian taxonomy and classification. They point out that a combination of factors, including morphological, vocal, and genetic, need to be considered in greater depth, with
additional sampling, to determine if the petitioned taxonomic classification should be accepted, and we are in agreement with these comments. Given the uncertainty and lack of clarification found in the best available scientific and commercial information, we rely on the “biological expertise of the Department and the scientific community concerning the relevant taxonomic group” (50 CFR 424.11(a)).
In summary, we find that there is considerable uncertainty as to whether the genetic differentiation found at the far ends of the pygmy-owl's distribution represented by Arizona and Texas are adequate to define the eastern and western distributions as separate subspecies. These differences may simply represent isolation by distance with a clinal gradation of genetic differentiation between the two extremes of the range, which would be inconsistent with the existence of two different subspecies. Therefore, the best available scientific and commercial information does not suggest that genetic differentiation reported by Proudfoot
et al.
(2006a; 2006b, entire) and König
et al.
(1999, entire) supports their proposed
Glaucidium ridgwayi cactorum
subspecies classification at this time. Future work and studies may clarify and resolve these issues, but, in the meantime, we will continue to use the currently accepted distribution of
G. brasilianum cactorum
as described in the 1957 AOU checklist and various other publications (Johnsgard 1988, p. 159; Millsap and Johnson 1988, p. 137; Oberholser 1974, p. 452; Friedmann
et al.
1950, p. 145). The Service accepted this information under the previous listing of the pygmy-owl (62 FR 10730). We, therefore, reject the petitioned listing of a western subspecies of pygmy-owl,
G. r. cactorum,
as an insufficiently supported taxonomic subspecies at this time.
The following discussion will examine the potentially listable entities of
Glaucidium brasilianum cactorum,
the currently recognized subspecies of pygmy-owl.
Distribution and Status
The currently accepted distribution of the pygmy-owl is described as south central Arizona and southern Texas in the United States, south through the Mexican States of Sonora, Sinaloa, Nayarit, Jalisco, Colima, and Michoacán on the west and Nuevo Leon and Tamaulipas on the east (Figure 1). Available information on the specific distribution of the pygmy-owl within this general area is not comprehensive, especially in the southern portions of Mexico. As described below, we have relatively detailed information on pygmy-owl distribution in the United States and Sonora, Mexico. The following is a description of the available information we have related to the distribution of the pygmy-owl.
The cactus ferruginous pygmy-owl is the northernmost subspecies of the ferruginous pygmy-owl. This subspecies was originally described as being common in the lower Rio Grande River in southern Texas (Oberholser 1974, p. 452) and along the Salt and Gila Rivers in central Arizona (Fisher 1893, p. 199; Breninger 1898, p. 128; Gilman 1909, p. 148). In Arizona and Texas, apparent range and population declines have occurred, reducing the current distribution of the pygmy-owl in these areas (Oberholser 1974, p. 452; Monson and Phillips 1981, p. 72; Proudfoot and Johnson 2000, p. 3). Historical records for the pygmy-owl in Arizona span at least five counties in southern and south-central Arizona, including Maricopa, Pima, Pinal, Santa Cruz and Yuma Counties (Johnson
et al.
2003, p. 394). Most of the historical (pre-1900) and recent (post-1990) records are from Pima County. Between 1872 and 1971, a total of 56 published records or specimens were recorded for Arizona. Of those, almost half (27) were from Pima County (Johnson
et al.
2003, pp. 392-395). Although the pygmy-owl was historically recorded primarily from lowland riparian habitats, all recent records are from upland and xeroriparian (vegetation community in drainages associated with seasonal or intermittent water) Sonoran desertscrub (Abbate
et al.
2000, pp. 15-16, Service 2009b, p. 1: 2011, p. 1).
Some information provided by the public suggested that the pygmy-owl is an obligate wet riparian species in south-central Arizona and a preferential wet riparian species in southern Arizona, tying its distribution to these types of areas. In addition, the information states that recent records in upland habitats have occurred primarily in areas associated with “cultivated riparian” habitats resulting from the human influences of irrigation and ornamental plantings, such as in suburban areas of Tucson (Johnson and Carothers 2008b, pp. 13-14). We agree that riparian ecosystems provide important pygmy-owl habitat within its range. However, we disagree with the suggestion that pygmy-owls are riparian obligates, and thus limited in occurrence to these areas. For example, there are numerous recent locations in which pygmy-owls were detected in Sonoran desert uplands and semi-desert grasslands of southern Pinal County, Avra Valley, Altar Valley, Cabeza Prieta National Wildlife Refuge, Organ Pipe Cactus National Monument, and northern Sonora that are not in proximity to “cultivated riparian” or naturally occurring hydro- or mesoriparian (wet riparian) habitats.
Two members of the public provided extensive information in support of the idea that pygmy-owls have never been common in Arizona; therefore, the current low numbers and reduced distribution are not sufficient reason to determine that the pygmy-owl is endangered in Arizona (James 2008, pp. 8-10; Parker 2008, pp. 2-10). This conclusion is based on the historical records from early naturalists and ornithologists regarding their observations or collections of pygmy-owls or their nests or eggs, or the lack thereof. Specifically, this information points out that a number of early naturalists or ornithologists that made trips of various lengths and in various locations in Arizona where pygmy-owls would have been expected to occur did not make mention of observing pygmy-owls in their trip reports (James 2008, pp. 46-48; Parker 2008, pp. 6-8). We appreciate the effort and research represented by this information. It provides an excellent summary of historical ornithological efforts in Arizona. In assessing the information provided, we must determine if it is comparable to the information currently available on pygmy-owl numbers and distribution in Arizona. Current information comes from extensive surveys focused on locating only pygmy-owls using tape-playback or call imitation to locate the owls. We can find no evidence from the information provided that this same effort or methodology was used to locate pygmy-owls in the historical record; thus comparison with current surveys is not appropriate.
We do not discount the ability of early naturalists and ornithologists to find and identify pygmy-owls. However, finding pygmy-owls was not the objective of the trips reported in the literature, and unfortunately, most of these early reports do not contain enough information for us to determine that the effort was adequate to find pygmy-owls if they were present or that the absence of documentation of pygmy-owls truly means that no pygmy-owls were encountered. Additional information received from the public points out the problems in interpreting these early reports, “While certainly instructive as to the critical value of surface water diversions, irrigation, and agriculture to Cactus ferruginous pygmy owls, lack of necessary specific information prevents Breninger's 1898
account from serving as a source of support for the petitioner's claim that this owl was historically common across the lowlands of central and southern Arizona. This is because Breninger neither shows how much time he spent in the field nor the locations he actually visited along either the Salt and Gila Rivers that caused him to conclude that Cactus ferruginous pygmy owls were then “of common occurrence” “among the growth of cottonwood” that fringed both on a highly localized basis” (Parker 2008, pp. 3-4).
While early records provide information that shows the range of the pygmy-owl has contracted in Arizona, this conclusion relies on information at a large scale and is not dependent on specific population numbers, only presence or absence. The logical assumption may follow that pygmy-owl numbers are likely reduced as well. However, these early records do not have enough specific information for us to quantify historical pygmy-owl population numbers in a way that allows comparison to our current information. Glinski (1998, p. 3) provides a summary of this issue in
The Raptors of Arizona,
“From the perspective of the variety and numbers of raptors, what did Arizona's landscape harbor two centuries ago? Is the answer to this question in the early literature? Unfortunately, no. Detailed records that accurately depict the status of Arizona raptors before 1970 are entirely lacking. The records of early explorers are full of errors, and later interpretations of them have added to the problem (G.P. Davis 1982).”
We received information from various agencies and municipalities that contained survey results from Arizona indicating that the pygmy-owl is likely absent from some areas in Maricopa and Pima Counties. Survey data submitted by the USDA Forest Service covering over 4,050 hectares (ha) (10,000 acres (ac)) in a 6-year period on the Tonto National Forest in Maricopa County detected no pygmy-owls (USFS 2008, p. 1). Burger (2008, p.1) indicated that the Arizona Game and Fish Department (AGFD) had conducted 3 years of surveys in Maricopa County without any pygmy-owl detections. Annual pygmy-owl surveys have been conducted by the Air Force on the Barry M. Goldwater Range of southwestern Arizona from 1993 to the present with no verified pygmy-owl detections (Uken 2008, p. 1). The Pima County Department of Transportation conducts pygmy-owl surveys for their capital improvement projects. These pygmy-owl surveys are associated with specific projects, and do not represent systematic surveys throughout Pima County. To date, they have conducted 383 surveys at 152 locations in Pima County with no detections (Pima County 2008, p.1). Some of the above surveys, and other negative surveys conducted throughout Arizona since 1997, occurred in areas where the pygmy-owl was historically located. This provides strong evidence that the current range of the pygmy-owl in Arizona has contracted.
Currently in Arizona, the pygmy-owl is found only in portions of Pima and Pinal Counties. The Arizona Breeding Bird Atlas reports confirmed occurrences of the pygmy-owl in only three blocks distributed in Pima and Pinal Counties (Arizona Breeding Bird Atlas (ABBA) 2005, p. 219). Twelve other blocks recorded probable (3) or possible (9) occurrences, but none occurred outside of Pima and Pinal Counties (ABBA 2005, p. 219). Recent surveys indicate that probably fewer than 50 adult pygmy-owls exist in the state, with 10 or fewer nest sites on an annual basis (Abbate
et al.
2000, pp. 15-16, AGFD unpublished data). However, since the pygmy-owl was delisted in 2006 (71 FR 194521; April 14, 2006), surveys, monitoring, and other research on pygmy-owls has declined. Limited survey and monitoring in Arizona from 2009 to 2011 documented that pygmy-owls still occupy historical locations in the Altar Valley, Avra Valley, and Organ Pipe Cactus National Monument, all within Pima County (Service 2009b, p. 1; Tibbitts 2011, p. 1; Service 2011, p. 1). Comprehensive surveys have not been conducted on the Tohono O'odham Nation (Nation), which is located in the central portion of both the historical and current distribution of pygmy-owls in Arizona. However, a number of surveys have been completed for various utility projects on the Nation, and the pygmy-owl is known to occur there. Distribution of the data from these surveys has been restricted by the Nation and is not available for analysis. There are large areas of suitable habitat on the Nation, but the information we have indicates that pygmy-owls are patchily distributed, just as in other areas of the State, and occur at similar densities.
In summary, because the early records found in the literature provide no basis for consistent interpretation, the statements that the pygmy-owl was “not uncommon,” “of common occurrence,” and “fairly numerous” in lowland central and southern Arizona may be as appropriate as the commenter's interpretation that the pygmy-owl was never common in Arizona. The bottom line is that these early records provided no quantifiable information on which to base trends in pygmy-owl populations. Consequently, we must base our evaluation of the current pygmy-owl status on the best available scientific and commercial data, which is the information that does, at least, provide some ability to quantify pygmy-owl population numbers. Regardless of the lack of quantified historical data, the early records found in the literature give us some idea of the historical distribution of the pygmy-owl in Arizona that, when compared to the current distribution, has unquestionably been reduced.
In Texas, the pygmy-owl was formerly common in the Rio Grande delta. Griscom and Crosby (1926, p. 18) reported that the pygmy-owl was considered a “common breeding species” in the Brownville region of southern Texas. Even as late as 1950, Friedman
et al.
(1950, p. 145) considered the pygmy-owl to be “a very common breeding bird.” However, Oberholser (1974, pp. 451-452) indicates that agricultural expansion and subsequent loss of native woodland and thornscrub habitat, beginning in the 1920s, preceded the rapid demise of the pygmy-owl populations in the Rio Grande delta. By the 1970s, the pygmy-owl was encountered only rarely in Texas.
Nonetheless, Wauer
et al.
(1993, pp. 1074-1076) indicate that private ranches in Kenedy and Brooks Counties in Texas support a “large and apparently thriving population of ferruginous pygmy-owls.” Currently, the pygmy-owl is most consistently found only in the southernmost counties in Texas, mainly in Starr and Kenedy Counties (Tewes 1992, p. 21; Oberholser 1974, p. 451). More recent work documents occupancy in Brooks and Kenedy Counties on the King Ranch and adjacent ranches in Texas (Proudfoot 1996, p. 6; Mays 1996, p. 29). Population estimates in Texas include estimates of greater than 100 owls in Kleberg County (Tewes 1992, p. 24), 654 pairs in Kenedy, Brooks, and Willacy Counties (Wauer
et al.
1993, p. 1074), and 745 to 1,823 pygmy-owls on ranches in Kenedy and Brooks Counties (Mays 1996, p. 32).
Recent concern about the populations in Texas has been raised because of an apparent decline in the number of pygmy-owl nestlings banded as part of an ongoing nest box study in Texas (Proudfoot 2010, p. 1). The numbers of nestlings banded at more than 200 nest boxes in 2003 and 2004 were 84 and 96 respectively. The numbers suggest a steady decline from 2004 to 2010, with 25 and 24 nestlings banded in 2009 and
2010, respectively (Proudfoot 2010, p. 1). This represents an approximate 70 percent decline in the number of nestlings banded over an 8-year period. Proudfoot (2011b, p. 1) indicates this decline is likely the result of the loss of suitable habitat around nest boxes due to recent hurricanes and fires. Without a more comprehensive survey effort in southern Texas, we cannot definitively state that the overall population of pygmy-owls in south Texas matches the decline of nestlings documented during this nest box study. However, it does raise our level of concern for this population. More work is needed in Texas to determine the overall population status and the extent of habitat loss and fragmentation. It may simply be that the pygmy-owls in these areas have moved to adjacent suitable habitat as former habitat and the associated nest boxes have been destroyed.
The pygmy-owl occurs in portions of eight States in Mexico. The pygmy-owl was thought to be uncommon throughout much of Sonora (Russell and Monson 1998, p. 141; Hunter 1988, pp. 1-6). However, recent surveys and capture efforts have shown that the pygmy-owl commonly occurs in both northern and southern Sonora, but is uncommon or absent in central Sonora (Flesch 2003, p. 39; AGFD 2008a, p.6; Service 2009a, p. 1). The highest densities of pygmy-owls occurred in the Sinaloan deciduous forest of southern Sonora (Flesch 2003, p. 42). Flesch (2003, p. 39) documented 438 males, 74 females, and 12 pygmy-owls of unknown sex along 1,113 kilometers (km) (1,780 miles (mi)) of transects in Sonora, and an additional 112 pygmy-owls incidentally detected.
During capture efforts in 2008, AGFD (2008a, p. 6) documented multiple pygmy-owls commonly responding at capture sites in the thornscrub and tropical deciduous forests of southern Sonora. In areas of central Sonora sampled by AGFD, some sites had no pygmy-owl responses, but responses increased as sampling moved into northern Sonora. These results are similar to patterns of occupancy documented by Flesch (2003, p. 40). However, it is clear that the number and density of pygmy-owls is higher in the thornscrub and deciduous forest community types than in the Sonoran desert community type. This occurrence and distribution agrees with conclusions found in the literature (Hunter 1988, p. 7; Russell and Monson 1988, p. 141; Shaldach 1963, p. 40). A total of 119 pygmy-owls were captured by AGFD over 15 days of trapping in northern Sinaloa and Sonora (AGFD 2008a, p. 6). The most recent monitoring of pygmy-owls in northern Sonora showed that, in 2010, sites sampled had the highest occupancy rates in the past 10 years at nearly 64 percent (Flesch 2011, p. 1). However, early results from the 2011 monitoring show occupancy of these same sites at around 50 percent, not far from the 10-year low of 45.7 percent (Flesch 2011, p. 1).
In summary, recent surveys and research in northwestern Mexico indicate that numbers and density of pygmy-owls are higher in thornscrub and tropical deciduous forest communities of southern Sonora and Sinaloa than in the Sonoran desertscrub and semi-desert grassland vegetation communities of the Sonoran Desert Ecoregion (Flesch 2003, pp. 39-42; AGFD 2008a, p. 6).
The best available information we have from the literature for the southern portion (areas south of Sonora and northern Sinaloa) of the pygmy-owl range indicates that pygmy-owls are one of the most common birds collected in these areas (Cartron
et al.
2000, p. 5; Enriquez-Rocha
et al.
1993, p. 154; Binford 1989, p. 132; Hunter 1988, p. 7; Johnsgard 1988, p. 161; Oberholser 1974, p. 451; Schaldach 1963, p. 40). It is important to note, however, that most of these references apply to the ferruginous pygmy-owl as a species and not to the
cactorum
subspecies specifically. However, the more recent survey, monitoring, and capture work discussed above all occurred within the range of the
cactorum
subspecies.
Tewes (1993, pp. 15-16) provides the most current information on pygmy-owls in northeastern Mexico. During surveys in 1991, he estimated 96 pygmy-owls in association with 142 plots at 12 locations (Tewes 1993, pp. 15-16). He concludes that no published empirical evidence suggests any change in the distribution of this species in Texas or northeastern Mexico, although the likelihood of finding pygmy-owls is low in some historically occupied areas (Tewes 1993, p. 22).
In addition, pygmy-owls are not evenly distributed across their current range; rather they tend to be patchily distributed across the landscape. Pygmy-owl populations, particularly in the northern portion of its range, likely function as metapopulations (a group of spatially separated populations that act at some levels as a single large population). Genetic and population support for individual groups of pygmy-owls likely occurs as a result of dispersal. Therefore, habitat connectivity among these population groups is important to maintain genetic diversity, as well as demographic support. Interaction among these population groups likely varies with distance, but pygmy-owls have been documented to disperse up to 260 km (161 mi.) (AGFD 2008a, p. 5). Individual pygmy-owl groups throughout the range are important to the survival of the subspecies as a whole in providing metapopulation support.
In conclusion, pygmy-owl distribution in the United States has contracted, with pygmy-owls no longer found in Maricopa, Cochise, Yuma, and Santa Cruz Counties in Arizona, nor in the Lower Rio Grande Valley in Texas. Despite this range contraction in the United States, pygmy-owls remain in Arizona and Texas. Survey results for Arizona indicate that approximately 50 adult pygmy-owls remain. In addition, there are a few large expanses of Arizona with suitable pygmy-owl habitat that have not been completely surveyed or for which pygmy-owl information is not available for evaluation. Pygmy-owl populations in Texas are estimated to range up to 1,800 birds, although there have been some declines in pygmy-owl nestlings associated with a nest box study in Texas. Pygmy-owls are still found in Sonora and northern Sinaloa, with higher densities reported in thornscrub and dry tropical forested areas compared to the arid desert areas. Based on Tewes study (1993, entire), pygmy-owls still occupy suitable habitat in northeastern Mexico and the pygmy-owl's distribution remains unchanged in Texas and northeastern Mexico. In addition, it appears that pygmy-owls still occur in the same areas of Mexico reported in the literature, suggesting that the current distribution is similar to the historical distribution. The available information, although dated, suggests that pygmy-owls remain common in the southern portion of their range.
Habitat
Pygmy-owls are found in a variety of vegetation communities, including Sonoran desertscrub and semidesert grasslands in Arizona and northern Sonora, thornscrub and dry deciduous forests in southern Sonora south to Michoacán, and Tamaulipan brushland in Texas and northeastern Mexico. However, available information regarding specific pygmy-owl habitat elements within these vegetation communities is limited to Arizona, Texas, and northern Sonora.
In Arizona, pygmy-owls rarely occur below 300 meters (m) (1,000 feet (ft)) or above 1,200 m (4,000 ft) (Proudfoot and Johnson 2000, p. 5), except perhaps during dispersal (AGFD 2008b, p. 3). Historically, in Arizona, the pygmy-owl
nested in Fremont cottonwood-mesquite forests and mesquite bosques (woodlands) associated with major drainages and their tributaries and the subspecies is considered by some to be a preferential riparian nesting species. The pygmy-owl in Arizona also occupies upland Sonoran desertscrub, often associated with xeroriparian areas. Species associated with these areas are
Prosopis
spp. (mesquite),
Parkinsonia
spp. (palo verde),
Acacia
spp. (acacia),
Olneya tesota
(ironwood), and
Carnegiea gigantea
(saguaro cactus) (Proudfoot and Johnson 2000, p. 5).
In Texas, the pygmy-owl was historically found in
Prosopis
spp.,
Ebenopsis ebano
(ebony), and
Arundinaria gigantea
(cane) along the Rio Grande River, and a more general distribution in riparian trees, brush, palm, and mesquite thickets (Oberholser 1974, p. 451). It is now found primarily in undisturbed live oak-mesquite forests and mesquite brush, ebony, and riparian areas of the historical Wild Horse Desert north of Brownsville, Texas (Proudfoot and Johnson 2000, p. 5).
In Mexico, the pygmy-owl occurs from sea level to 1,200 m (4,000 ft) (Friedmann
et al.
1950, p. 145). In Sonora, it was originally common in the lower Sonoran and Tropical Zones, primarily in giant cactus associations (van Rossem 1945, p. 111). The subspecies is resident throughout most of the desertscrub, tropical thornscrub, and dry subtropical forests of Sonora, being most common in the latter association (Russell and Monson 1998, p. 141). The pygmy-owl is absent from tropical deciduous forests and higher vegetation zones in west Mexico, where it is replaced by the least pygmy-owl (
Glaucidium minutissimum
) and the northern pygmy-owl (
G. gnoma
) (Schaldach 1963, p. 40; Buchanan 1964, pp. 104-105), as well as the Colima pygmy-owl (
G. palmarum
) (Howell and Robbins 1995, pp. 19-20). Dry, subtropical forests provide important pygmy-owl habitat elements, as evidenced by pygmy-owls being more common in this vegetation community type than in other community types in Mexico. The dry, subtropical forests comprise the majority of the pygmy-owl's southern range in Mexico. The presence of large trees and columnar cacti for nesting, and diversity of cover and prey types, contribute to the value of dry subtropical forests as pygmy-owl habitat.
The pygmy-owl is a creature of edges found in semi-open areas of thorny scrub and woodlands in association with giant cacti, scattered patches of woodlands in open landscapes, mostly dry woods, and evergreen secondary growth (König
et al.
1999, p. 373). It is often found at the edges of riparian and xeroriparian drainages and even habitat edges created by villages, towns, and cities (Proudfoot and Johnson 2000, p. 5; Abbate
et al.
1999, pp. 14-23). The pygmy-owl is a secondary cavity nester, and nests occur within woodpecker holes and natural cavities in giant cacti, but also in trees and even in a sand bank (Flesch 2003, pp. 130-132; Proudfoot and Johnson 2000, p. 11; Russell and Monson 1998, p. 141; Johnsgard 1988, p. 162). Tewes (1992, p. 22) contends that status and occurrence of the pygmy-owl is related to the availability of nest cavities.
While native and nonnative plant species composition differs among the various locations within the range of the pygmy-owl, there are certain unifying characteristics such as the presence of vegetation in fairly dense thickets or woodlands; the presence of trees, saguaros,
Stenocereus thurberi
(organ pipe cactus), or other columnar cacti large enough to support cavities for nesting; and elevations typically below 1,200 m (4,000 ft) (Swarth 1914, p. 31; Karalus and Eckert 1974, p. 218; Monson and Phillips 1981, pp. 71-72; Johnsgard 1988, Enriquez-Rocha
et al.
1993, p. 158; Proudfoot 1996, p. 75; Proudfoot and Johnson 2000, p. 5). Large trees provide canopy cover and cavities used for nesting, and the density of mid- and lower-story vegetation provides foraging habitat and protection from predators and contributes to the occurrence of prey items (Wilcox
et al.
2000, pp. 6-9).
Life History
Usually, pygmy-owls first nest as yearlings (Proudfoot and Johnson 2000, p. 13; Abbate
et al.
1999, pp. 17-19), and both sexes breed annually thereafter. Territories normally contain several potential nest and roost cavities from which responding females select a nest. Hence, cavities per unit area may be a fundamental criterion for habitat selection. Historically, pygmy-owls in Arizona used cavities in cottonwood, mesquite, and ash trees, and saguaro cacti for nest sites (Millsap and Johnson 1988, pp. 137-138). Recent information from Arizona indicates nests were located in cavities in saguaro cacti for all but two of the known nests documented from 1996 to 2002 (Abbate
et al.
1996, p. 15; 1999, p. 41; 2000, p. 13; AGFD 2003, p. 1). Pygmy-owl nests in Texas were primarily in mesquite and live oak trees (Proudfoot 1996, pp. 36-38), and nests in Sonora, Mexico, were nearly always in columnar cacti (Flesch and Steidl 2002, p. 6). Pygmy-owls will also use nest boxes for nesting (Proudfoot 1996, p. 67).
Pygmy-owls begin courtship and advertisement calls early in the year from January into February. Nest selection then occurs, with eggs typically being laid from late March into June. Average clutch size as reported by Johnsgard (1988, p. 162) for the United States and Mexico was 3.3 (range 2 to 5, n = 43). In Texas, Proudfoot and Johnson (2000, p. 11) report an average clutch size of 4.9 (range 3 to 7, n = 58). First eggs hatch generally around mid-May, and fledging occurs from late-May through June. The first dispersal of fledglings in Arizona and Texas was documented as July 24th and August 14th, respectively (Proudfoot and Johnson 2000, p. 10). Pygmy-owl juveniles typically disperse at 8 weeks post-fledging. Males typically disperse shorter distances than females. Dispersal distance ranges from 2.5 to 20.91 km (1.55 to 13.00 mi) in Arizona (Abbate
et al.
2000, p. 21) and 16 to 31 km (9.6 to 18.6 mi) in Texas (Proudfoot and Johnson 2000, p. 13). One juvenile female pygmy-owl in Arizona recently dispersed a total of 260 km (161 mi) between August 2003 and April 2004 (AGFD 2008a, p. 5). In Sonora, Mexico, Flesch and Steidl (2007, p. 37) documented dispersal distances ranging from 1.1 to 19.2 km (0.7 to 11.5 mi).
Pygmy-owls are considered nonmigratory throughout their range. There are winter (November to January) pygmy-owl locations from throughout their historical range in Arizona (University of Arizona 1995, pp. 1-2; Snyder 2005, pp. 4-5; Abbate
et al.
1999, pp. 14-17; 2000, pp. 12-13) and also in Texas (Proudfoot 1996, p. 19; Mays 1996, p. 14). These winter records suggest that pygmy-owls are found within their home ranges throughout the year and that they do not migrate seasonally. The pygmy-owl is primarily diurnal (active during daylight) with crepuscular (active at dawn and dusk) tendencies.
The pygmy-owl is a perch-and-wait hunter. It is largely a generalist with regard to prey and diet. Oberholser (1974, p. 451) indicated that the pygmy-owl's diet included lizards, large insects, rodents, and birds (some as large as the owl). In Texas, insects, reptiles, birds, small mammals, and amphibians, to a lesser extent, are eaten by pygmy-owls (Proudfoot and Johnson 2000, p. 6). In Arizona, reptiles, birds, small mammals, and insects have all been recorded in the diet of the pygmy-owl (Abbate
et al.
1999, pp. 35-40). Seasonal and annual variations in diet occur throughout its range (Proudfoot
and Johnson 2000, p. 6; Abbate
et al.
1999, pp. 35-40).
The pygmy-owl is commonly mobbed (harassed) by many species of passerines, presumably in response to being a regular predator on those species (Proudfoot and Johnson 2000, p. 10; Abbate
et al.
1999, pp. 25-26; Hunter 1988, p. 1). The mobbing behavior of birds can often aid in locating a well hidden pygmy-owl, as multiple individuals and species will often participate in the mobbing and identify the perch of the pygmy-owl. The dark eye-spots on the back of the pygmy-owl's head may act to fend off mobbing or increase predatory efficiency by confusing prey (Heinrich 1987 in Proudfoot and Johnson 2000, p. 10).
Due to their small size and occurrence in similar habitats as many of their predators, pygmy-owls are preyed upon by a variety of species. Documented and likely predators in Texas and Arizona include raccoons (
Procyon lotor
), great horned owls (
Bubo virginianus
), Cooper's hawks (
Accipiter cooperii
), Harris' hawks (
Parabuteo unicinctus
), western screech owls (
Megascops kennicottii
), bull snakes (
Pituophis melanoleucus
), and domestic cats (
Felis domesticus
) (Abbate
et al.
1999, p. 27; Proudfoot and Johnson 2000, p. 10). Pygmy-owls may be particularly vulnerable to predation and other threats during and shortly after fledging (Abbate
et al.
1999, p. 50). Lifespan has been documented to be 7 to 9 years in the wild (Proudfoot 2009b, p. 1) and 10 years in captivity (AGFD 2009, p. 1).
Summary of Information Pertaining to the Five Factors Affecting the Pygmy-Owl Throughout Its Range
Section 4 of the Act (16 U.S.C. 1533) and implementing regulations (50 CFR 424) set forth procedures for adding species to, removing species from, or reclassifying species on the Federal Lists of Endangered and Threatened Wildlife and Plants. Under section 4(a)(1) of the Act, a species may be determined to be endangered or threatened based on any of the following five factors:
(A) The present or threatened destruction, modification, or curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued existence.
In making our 12-month finding on the petition we considered and evaluated the best available scientific and commercial information.
In considering whether the five statutory factors in section 4(a) might constitute threats, we must look beyond the mere exposure of the species to the factor and determine whether the species responds to the factor in a way that causes actual negative impacts to the species. If there is exposure to a factor, but no response, or only a positive response, that factor is not a threat. If there is exposure and the species responds negatively, the factor may be a threat and we then attempt to determine how significant a threat it is. If the threat is significant, it may drive or contribute to the risk of extinction of the species such that the species warrants listing as threatened or endangered as those terms are defined by the Act. This does not necessarily require empirical proof of a significant threat. The combination of exposure and some corroborating evidence of how the species is likely impacted could suffice. The mere identification of factors that could impact a species negatively is not sufficient to compel a finding that listing is appropriate; we require evidence that these factors are operative threats that act on the species to the point that the species meets the definition of threatened or endangered under the Act. A species may be threatened or endangered based on the intensity or magnitude of one operative threat alone or based on the synergistic effect of several operative threats acting in concert.
Through our five-factor analysis, we identified a number of factors negatively impacting the pygmy-owl or its habitat. To determine whether these impacts individually or collectively rise to the level of threats such that the pygmy-owl is in danger of extinction throughout its range, or likely to become so in the foreseeable future, we first considered whether these impacts to the subspecies were causing long-term, range-wide, population-scale declines in pygmy-owl numbers, or were likely to do so in the foreseeable future. Although some of these impacts seem significant individually, we found these impacts to be localized in their effects, but not placing the pygmy-owl in danger of extinction throughout its range now or in the foreseeable future. In other words, the severe impacts were restricted to an area that constitutes a relatively small portion of the pygmy-owl's range.
The detailed information we have on impacts covers only about 27 percent of the pygmy-owl's range. For this area, which includes Arizona and Texas in the United States, and Sonora and northern Sinaloa in Mexico, information describing the impacts to pygmy-owls was relatively complete. For the remaining 73 percent of the pygmy-owl range in Mexico, information regarding impacts to pygmy-owls was relatively sparse. The best available scientific and commercial information indicates that the impacts to pygmy-owls in the northern portion of their range are severe. However, the best available information indicates that pygmy-owls in the southern portion of their range remain common and that some of the threats that are severe in the northern portion of the species' range appear to be less severe or non-existent in the southern portion. Thus we conclude that pygmy owls are not threatened throughout their range, or likely to become so. The details supporting our conclusion are found in the following analysis.
Factor A: Present or Threatened Destruction, Modification, or Curtailment of Its Habitat or Range
For this factor, we evaluate available information related to impacts to pygmy-owl habitat throughout its range. Our evaluation identified general activities affecting or potentially affecting pygmy-owl habitat that included urbanization, nonnative species invasions, fire, agricultural development, wood cutting, improper grazing, border issues, and off-highway vehicle use. However, with the exception of the United States and Sonora, Mexico, detailed information related to these activities is limited, and we were unable to specifically evaluate the effects of many of these activities for much of the pygmy-owl's range in Mexico. The following discussion presents the best available information regarding these activities and their effects to pygmy-owl habitat.
Urbanization
Increasing human populations result in expanding urban areas. Urbanization causes permanent impacts on the landscape that potentially result in the loss and alteration of pygmy-owl habitat. Residential, commercial, and infrastructure development replace and fragment areas of native vegetation resulting in the loss of available pygmy-owl habitat and habitat connectivity needed to support pygmy-owl dispersal and metapopulation function. Increasing human populations require additional water, and increasing water consumption can reduce available surface and ground water needed to support pygmy-owl and pygmy-owl prey habitats. Added human presence on the landscape can potentially lead to increased pygmy-owl mortality through
introduced predators, collisions, etc. The following discussion presents the available information related to pygmy-owl habitat impacts associated with urbanization.
Human population growth results in the expansion of urbanization (Travis
et al.
2005, p. 2). Arizona's population increased by 394 percent from 1960 to 2000, and was second only to Nevada as the fastest growing State during this timeframe (Social Science Data Analysis Network (SSDAN) 2000, p. 1). Since 1990, Arizona's population has grown by 44 percent. From 1960 to 2000, population growth rates in Arizona counties where the pygmy-owl occurs, or recently occurred, have varied by county, but all are increasing: Maricopa (463 percent); Pima (318 percent); Pinal (54 percent); and Santa Cruz (355 percent) (SSDAN 2000).
Urban expansion and human population growth trends in Arizona are expected to continue into the future. The Maricopa-Pima-Pinal County areas of Arizona are expected to grow by as much as 71 percent in the next 15 years, creating rural-urban edge effects across thousands of acres of pygmy-owl habitat (AIDTT 2000, p. 10; BLM files-Lands Livability Initiative). In another projection, the Arizona population is expected to more than double within the next 20 years, compared to the 2000 population estimate (U.S. Census Bureau 2005, p. 1). Many cities and towns within the historical distribution of the pygmy-owl in Arizona already experienced substantial growth during the 8-year time span from 2000 to 2008: Town of Carefree (30.5 percent); Casa Grande (56 percent); Town of Cave Creek (44.2 percent); City of Eloy (22.3 percent); City of Florence (20.3 percent); City of Mammoth (45 percent); Town of Marana (139.9 percent); Town of Oro Valley (32.5 percent); and the Town of Sahuarita (507.3 percent) (U.S. Census Bureau 2008, pp. 1-4).
This population growth has spurred a significant increase in urbanization and development in these areas. Regional development is predicted to be high in certain areas within the distribution of the pygmy-owl in Arizona. In particular, a wide area from the international border in Nogales, through Tucson, Phoenix, and north into Yavapai County (called the Sun Corridor “Megapolitan” Area) is predicted to have 8 million people by 2030, an 82.5 percent increase from 2000 (Gammage
et al.
2008, pp. 15, 22-23). If build-out occurs as expected, it will encompass a substantial portion of the current and historical distribution of the pygmy-owl in Arizona.
Development pressure across Arizona has slowed due to the recent economic downturn and decline in the housing market. However, development will likely continue in the future, although perhaps at a slower pace than in the earlier part of this century. We also recognize that economic trends are difficult to predict into the future. The most recent draft Pinal County Comprehensive Plan (February 2009) acknowledges that the county is in the middle of the Sun Corridor Megapolitan and proposes four shorter-term growth areas in defining where development will likely occur over the next decade, but does not discourage growth outside of these areas (Pinal County Comprehensive Plan 2009, p. 109). Areas within two of the four growth areas (West Pinal and Red Rock) support historically occupied and recently occupied areas.
Because most of the pygmy-owl habitat in Texas occurs on private ranch lands, the impact of habitat loss and fragmentation of the remaining pygmy-owl habitat due to urbanization is greatly reduced. Some housing, ranch facilities, roadways, and utilities will undoubtedly be constructed with changing ranch plans, and this may affect individual pygmy-owl territories. However, the overall impact to pygmy-owl habitat from current rates of urbanization in Texas is much less than that in Arizona and parts of Mexico.
In Mexico, the greatest increases in population have occurred mostly in coastal resort areas, State capitals, and along the United States-Mexico border. In the Sonoran Desert Ecoregion of Mexico (a relatively homogeneous ecological area defined by similarity of climate, landform, soil, potential natural vegetation, hydrology, or other ecologically relevant variables), the human population nearly doubled between 1970 and 1990, to a total population of 6.9 million (Gorenflo 2002, p. 13). The Sonoran capital, Hermosillo, grew by 116 percent. When considering urban growth within individual biotic communities, the human population more than doubled in three of the seven major biogeographic communities of Mexico (Arizona Upland and Lower Colorado River Valley, Plains of Sonora, and Magdalena Plain) (Gorenflo 2002, p. 28), all of which provide important pygmy-owl habitat.
The United States-Mexico border region has a distinct demographic pattern of permanent and temporary development related to warehouses, exports, and other border-related activities, and patterns of population growth in this area of northern Mexico have been accelerated relative to other Mexican States (Pineiro 2001, pp. 1-2). This focuses development, and potential barriers or impediments to pygmy-owl movements, in a region that is important for pygmy-owl metapopulation support and other movements such as dispersal. The Arizona-Sonora border region's population growth is expected to reach 2.1 million (Walker and Pavlakovich-Kochi 2003, p. 1) in an area that will affect cross-border movement by pygmy-owls and other important population linkages needed to support the pygmy-owl metapopulation structure. Based on 1990 human population numbers, the land cover types currently most valuable to the pygmy-owl—Mesquite Bosque and Palo Verde-Mixed Cactus—were the most heavily human-populated in the Sonoran Desert Ecoregion. The Mesquite Bosque type makes up 8.2 percent of the area, but supports 10.4 percent of the human population. Similarly, the Palo Verde-Mixed Cactus type covers 29 percent of the area, but supports 49.4 percent of the population (Gorenflo 2002, p. 28).
Human activity, most notably in the past century, has dramatically altered the landscape of the Arizona-Sonora border, affecting both the quantity and quality of its ecological resources. Urbanization not only reduces the amount of open space, but impacts the biological value of areas (Walker and Pavlakovich-Kochi 2003, p. 3). The Sonoran border population has been increasing faster than that State's average and faster than Arizona's border population; between 1990 and 2000, the population in the Sonoran border municipios increased by 33.4 percent, compared to Sonora's average (21.6 percent) and the average increase of Arizona's border counties (27.8 percent). Urbanization has increased habitat conversion and fragmentation, which, along with immigration, population growth, and resource consumption, were ranked as the highest threats to the Sonoran Desert Ecoregion (Nabhan and Holdsworth 1998, p. 1).
Urbanization has also affected pygmy-owl habitat in other parts of Mexico. Trejo and Dirzo (2000, p. 133) indicate that areas of dry subtropical forests, important habitat for pygmy-owls in southwestern Mexico, have been used by humans through time for settlement and various other activities. The long-term impact of this settlement has converted these dry subtropical forests into shrublands and savannas lacking large trees, columnar cacti, and cover and prey diversity that are important pygmy-owl habitat elements Trejo and Dirzo (2000, p. 134) state that in Mexico dry tropical forest is the major type of tropical vegetation in the country,
covering over 60 percent of the total area of tropical vegetation. According to official governmental maps, about 8 percent (approximately 160,000 square km (61,776 square mi)) of this forest remained intact by the late 1970s, and an assessment made at the beginning of the present decade suggested that 30 percent of these tropical forests have been altered and converted to agricultural lands and cattle grasslands. The remaining forests are restricted to steep slopes where it is not likely that land will be cleared for additional agricultural or development purposes (Allnutt 2001, p.3). However, the information about the current actual extension and condition of dry tropical forests in Mexico is unclear due to confusion in their classification and difficulty using remote sensing to delineate intact dry forest (Allnutt 2001, p. 3). The best available information indicates that there are still expanses of dry tropical forest along the Pacific coast in Mexico, including some areas below 1,200 m (4,000 ft) where pygmy-owls are found, but there has been loss of this forest type throughout Mexico.
The actual effects of urbanization on biodiversity are many and mutually reinforcing, including the aggravation of the “urban heat island effect”; the channelization or disruption of riverine corridors; the proliferation of exotic species; the killing of wildlife by automobiles, toxins, and pets; and the fragmentation of remaining patches of natural vegetation into smaller and smaller pieces that are unable to support viable populations of native plants or animals (Ewing and Kostyack 2005, pp. 1-2; Nabhan and Holdsworth 1998, p. 2). Human-related mortality (e.g., shooting, collisions, and predation by pets) increases as urbanization increases (Banks 1979, pp. 1-2; Churcher and Lawton 1987, p. 439). The above statements, while general in their nature, point out the vulnerability of habitats that support pygmy-owls and the impacts that urbanization can have on the extent and quality of available habitat. We would expect these types of impacts in areas that have experienced or are experiencing urban growth in or near pygmy-owl habitats. Not all areas in the United States and Mexico are experiencing this type of growth, especially in the southern portion of the pygmy-owl's range.
Development of roadways and their contribution to habitat loss and fragmentation is a particularly widespread impact of urbanization (Nickens 1991, p. 1). Data from Arizona and Mexico indicate that roadways and other open areas lacking cover affect pygmy-owl dispersal (Flesch and Steidl 2007, pp. 6-7; Abbate
et al.
1999, p. 54). Nest success and juvenile survival were lower at pygmy-owl nest sites closer to large roadways, suggesting that habitat quality may be reduced in those areas (Flesch and Steidl 2007, pp. 6-7).
Currently, most roadways in Sonora are relatively narrow. However, the Sonoran government is starting to implement plans to build new highways and other infrastructure improvements. Governor Bours of Sonora formed the Sonoran Strategic Projects Operator, in conjunction with other investors, to carry out the construction of highway improvements (Wild Sonora 2009, p. 2). Of specific concern related to pygmy-owl impacts is the recent improvement of the road between Saric, in the upper Rio Altar valley, and Sasabe, in the heart of the distribution of the pygmy-owl in northern Sonora. Instead of just paving the existing Altar/Sasabe road, a new highway was constructed resulting in an increase of habitat impacts and fragmentation (Wild Sonora 2009, p. 2). Another development project proposed for northern Sonora is the Quitovac toxic waste dump south of Organ Pipe Cactus National Monument that could accept up to 45,000 tons of toxic waste per year (Wild Sonora 2009, p. 7). The proposed site for this project is located in the vicinity of a rare spring in this very arid region that supports pygmy-owl habitat. There are documented pygmy-owls nesting at Quitovac (Flesch 2003, pp. 40-41). While this project is currently on hold, it represents the potential for impacts to pygmy-owls related to development and urbanization in Sonora.
Significant human population expansion and urbanization in the Sierra Madre foothill corridor may represent a long-term risk to pygmy-owls in northeastern Mexico. In Texas, the pygmy-owl occurred in good numbers until approximately 90 percent of the mesquite-ebony woodlands of the Rio Grande delta were cleared in 1910-1950 (Oberholser 1974, p. 452). Habitat removal in northeastern Mexico is widespread and nearly complete in northern Tamaulipas (Hunter 1988, p. 8). The pygmy-owl metapopulation structure is threatened by ongoing loss and fragmentation of habitat in this area. Urbanization has the potential to permanently alter the last major landscape linkage between the pygmy-owl population in Texas and those in northeastern Mexico (Tewes 1992, pp. 28-29).
With regard to Mexico, for those areas outside of Sonora and northeastern Mexico discussed above, human population growth in Sinaloa, Nayarit, Colima, and Jalisco are relatively slow compared to Sonora. The Sinaloan population grew at a rate of 0.9 percent over the last decade. The population in Nayarit grew at a rate of 1.8 percent over the last decade. The Jalisco population grew by 1.6 percent per year during 2000-2010. Colima, one of the smallest States in Mexico, has a total population of approximately 650,500 and grew annually at a rate of 1.9 percent over the last decade. These areas of Mexico are not experiencing the high growth rates of Sonora, and likely will not have the concurrent spread of urbanization in the foreseeable future. In addition, most of the growth is taking place in the large cities, and not the rural areas of these countries (
http:www.citypopulation.de/Mexico-Cities.html
). Also, some of the large cities of the southern Mexican States, such as Guadalajara in Jalisco and Morelia in Michoacán, are not within the range of the pygmy-owl, so their growth would not be affecting pygmy-owl habitat. The rural areas likely contain the remaining habitat for the pygmy-owl. It is reasonable to assume that slow or stagnant population growth will result in fewer developments and infrastructure projects, such as new highways, or destruction and fragmentation of habitat on a landscape scale. The impacts associated with urbanization are, therefore, much reduced and less severe in this portion of the pygmy-owl's range. While the magnitude of the impacts associated with urbanization are significant in Arizona and northern Mexico, we would expect these impacts to be much reduced in the remaining 73 percent of the pygmy-owl's range in Mexico and we expect these impacts to remain less significant in this part of its range into the foreseeable future because of the difference in population growth.
Nonnative Invasive Species
The invasion of nonnative vegetation, particularly nonnative grasses, has altered the natural fire regime over the Sonoran portion of the pygmy-owl range. As a result, fire has become a significant threat to the native vegetation of the Sonoran Desert. Esque and Schwalbe (2002, pp. 180-190) discuss the effect of wildfires in the Arizona Upland and Lower Colorado River subdivisions of Sonoran desertscrub, which comprise the primary portions of the pygmy-owl's range within Sonoran desertscrub. The widespread invasion of nonnative annual grasses appears to be largely responsible for altered fire regimes that have been observed in these communities, which are not adapted to fire (Esque and Schwalbe 2002, p. 165). In areas comprised entirely of native
species, ground vegetation density is mediated by barren spaces that do not allow fire to carry across the landscape. However, in areas where nonnative species have become established, the fine fuel load is continuous, and fire is capable of spreading quickly and efficiently (Esque and Schwalbe 2002, p. 175). Nonnative annual plants prevalent within the Sonoran range of the pygmy-owl include
Bromus rubens
and
B. tectorum
(brome grasses) and
Schismus
spp. (Mediterranean grasses) (Esque and Schwalbe 2002, p. 165).
Brassica tournefortii
(Sahara mustard) is an Old World forb that can cover 100 percent of the ground under certain conditions (ASDM 2009, p. 1). In 2006, fires that burned thousands of acres of Sonoran desertscrub in southwestern Arizona had Sahara mustard as the primary fuel. However, the nonnative species that is currently the greatest threat to vegetation communities in Arizona and northern Sonora, Mexico is the perennial
Pennisetum ciliare
(buffelgrass)
,
which is prevalent and increasing throughout much of the Sonoran range of the pygmy-owl (Burquez and Quintana 1994, p. 23; Van Devender and Dimmit 2006, p. 5).
Buffelgrass is an Indo-African grass introduced to Mexico between 1940 and 1960 (Burquez
et al.
1998, p. 25). The distribution of this grass has been supported and promoted by governments on both sides of the United States-Mexico border as a resource to increase range productivity and forage production. Buffelgrass is first established by stripping away the native desertscrub and thornscrub (Franklin
et al.
2006, p. 69). Following establishment, it fuels fires that destroy Sonoran desertscrub, thornscrub, and, to a lesser extent, tropical deciduous forest; the disturbed areas are quickly converted to open savannas composed entirely of buffelgrass. Buffelgrass is now fully naturalized in most of Sonora, southern Arizona, and some areas in central and southern Baja California (Burquez-Montijo
et al.
2002, p. 131), and now commonly spreads without human cultivation (Arriaga
et al.
2004, pp. 1509-1511; Perramond 2000, p. 131; Burquez
et al.
1998, p. 26).
However, buffelgrass is adapted to dry, arid conditions and does not grow in areas with high rates of precipitation or high humidity, above elevations of 1,265 m (4,150 ft), and in areas with freezing temperatures. Areas that support pygmy-owls south of Sonora and northern Sinaloa typically are wetter and more humid, and the best available information does not indicate that buffelgrass is invading the southern portion of the pygmy-owl's range. Buffelgrass is most often located on steep, rocky, south-facing slopes, with poor soil development (Van Devender and Dimmitt 2006, pp. 25-26). Surveys completed in Sonora and Sinaloa in 2006 noted buffelgrass was present in Sonora and northern Sinaloa, but the more southerly locations were noted as sparse or moderate (Van Devender and Dimmitt 2006, p. 7). This was in comparison to northerly sites in Sonora that were rated as dense with buffelgrass. As such, this nonnative species only significantly affects a portion of the pygmy-owl's range. The best available information indicates that buffelgrass is not significantly affecting areas in Mexico beyond Sonora, and northern Sinaloa.
Buffelgrass is not only fire-tolerant (unlike native Sonoran Desert plant species), but is actually fire-promoting (Halverson and Guertin 2003, p. 13). Invasion sets in motion a grass-fire cycle where nonnative grass provides the fuel necessary to initiate and promote fire. Nonnative grasses recover more quickly than native grass, tree, and cacti species and cause a further susceptibility to fire (D'Antonio and Vitousek 1992, p. 73; Schmid and Rogers 1988, p. 442). While a single fire in an area may or may not produce long-term reductions in plant cover or biomass, repeated wildfires in a given area, due to the establishment of nonnative grasses, are capable of ecosystem type-conversion from native desertscrub to nonnative annual grassland, and render the area unsuitable for pygmy-owls and other native wildlife due to the loss of trees and columnar cacti and reduced diversity of cover and prey species (Brooks and Esque 2002, p. 336). Buffelgrass competes with neighboring native species for space, water, and nutrients (Halverson and Guertin 2003, p. 13; Williams and Baruch 2000, pp. 128-135; D'Antonio and Vitousek 1992, pp. 68-72). Buffelgrass conversion is associated with increased soil erosion and changes in nutrient dynamics and primary productivity (Abbot and McPherson 1999, p. 3). These changes make it more difficult for native vegetation to reestablish, even if the conversion process or fires are discontinued (Franklin
et al.
2006, p. 69; Rogers and Steele 1980, pp. 17-18).
Within the past 15 years, the establishment of nonnative grasslands has been identified as the most serious threat to the biological diversity of the Sonoran Desert (Burquez and Quintana 1994, p. 23). Economic subsidies from the State of Sonora and low-interest loans from banks made funds available for more widespread plantings of buffelgrass in the 1980s (Camou-Healy 1994). By 1997, more than 1 million ha (2.5 million ac) of desertscrub and thornscrub (both communities occupied by the pygmy-owl) had been cleared in central Sonora to plant buffelgrass, and more than 2 million ha (5 million ac) were scheduled for future vegetation conversion (Burquez and Quintana 1994, p. 23; Johnson and Navarro 1992, p. 118), often as part of government programs to support the ranching industry (Van Devender
et al.
1997, p. 3). Researchers during this time period predicted that, if not halted, this practice of buffelgrass planting will permanently change the landscape of the Sonoran desert and deplete its associated biological diversity (Burquez and Quintana 1994, p. 23). Also, given the government subsidies to establish exotic grasslands in order to maintain large cattle herds, and to support marginal cattle ranching, it is less likely that control measures will be implemented, and the desertscrub and thornscrub in Sonora will probably be replaced in the near term by ecosystems with significantly lower species diversity and reduced structural complexity (Burquez and Martinez-Yrizar 1997, p. 387).
More recent figures indicate that this is indeed occurring, with buffelgrass present in more than two-thirds of Sonora, and 1.6 million ha (4 million ac) having been deliberately cleared and seeded with the species (Burquez-Montijo
et al.
2002, p. 132). A 2006 publication estimates that 1.8 million ha (4.5 million ac) have been converted to buffelgrass in Sonora, and that between 1990 and 2000, there was an 82 percent increase in buffelgrass coverage (Franklin
et al.
2006, pp. 62, 66). Buffelgrass pastures have doubled in area in Sonora approximately every 10 years since 1973 (Franklin
et al.
2006, p. 67) and the conversion to buffelgrass is expected to continue into the foreseeable future.
It is not only Sonoran desertscrub communities in Sonora and northern Sinaloa that are impacted by the spread of buffelgrass. Another unique vegetation community in this region, dry subtropical forests, are being lost and fragmented due to the planting of buffelgrass in association with cattle ranching, which results in vast tracts of forest being removed and replaced by buffelgrass (Allnut
et al.
2001, pp. 3-4).
Buffelgrass invasion in the United States is such an urgent and significant issue that the Governor of Arizona, and nearly all southern Arizona municipalities and agencies have joined together to address the issue. The Governor formed the Arizona Invasive Species Advisory Council in 2005, and
the Southern Arizona Buffelgrass Working Group developed the Southern Arizona Buffelgrass Strategic Plan in 2008 (Buffelgrass Working Group 2008) in order to coordinate the control of buffelgrass. Because of its negative impacts to native ecosystems, buffelgrass was declared a noxious weed by the State of Arizona in March 2005. It is not currently known whether these programs will be successful in controlling buffelgrass invasion.
The impacts of buffelgrass establishment and invasion are substantial for the pygmy-owl in the United States and Sonora because conversion results in the loss of all important habitat elements, particularly columnar cacti and trees that provide nest sites. Buffelgrass invasion and the subsequent fires eliminate most columnar cacti, trees, and shrubs of the desert (Burquez-Montijo
et al.
2002, p. 138). This elimination of trees, shrubs, and columnar cacti from these areas is a significant negative impact and potentially a threat to the survival of the pygmy-owl in the northern portion of its range, as these vegetation components are necessary for roosting, nesting, protection from predators, and thermal regulation. Because tree canopy cover is an important pygmy-owl habitat feature, the fact that buffelgrass fires reduce the number of tree-dominated patches and the recruitment opportunities for those native species dependent on them [such as saguaros] (Burquez and Quintana 1994, p. 11), is significant. Franklin
et al.
(2010, p. 7) report significant changes in vegetation structure as a result of creating buffelgrass pastures for grazing. There were 90 percent fewer trees and shrubs of the size used by pygmy-owls (2 to 5 m (6 to 15 ft) tall) in buffelgrass pastures as compared to native vegetation communities. Loss of diversity and availability of prey species due to conversion are also detrimental (Franklin
et al.
2006, p. 69; Avila Jimenez 2004, p. 18; Burquez-Montijo
et al.
2002, pp. 130, 135).
Some information we received from the public downplays the significance of the conversion of Sonoran desertscrub to buffelgrass savannas on pygmy-owl habitat by stating that there is no indication that the conversion is occurring in areas occupied by the pygmy-owl (Johnson and Carothers 2003, pp. 6-7). However, when compared to the maps of current and predicted buffelgrass invasion in Sonora found in Arriaga
et al.
(2003, Figure 1), the distribution of pygmy-owl locations from Flesch (2003, Figure 2), AGFD (2008a, p. 1), and Westland Resources (2008, Figure 4), as well as the known pygmy-owl locations and the documented occurrence of buffelgrass in Tucson, Avra Valley, Altar Valley, Organ Pipe Cactus National Monument, Pinal County, the Tohono O'odham Nation, and Sonora and northern Sinaloa show that there is almost 100 percent overlap in the areas occupied by pygmy-owls and the areas under greatest threat from buffelgrass invasion. One of the principle reasons that nonnative plants pose such a significant negative impact on the pygmy-owl in its northern range, and the native plant communities on which they depend, is because few, if any, reasonable methods currently exist to control the ongoing invasion of these plants or to remediate areas where they are already established. Mechanical removal, herbicides, and fire have all been tested for their effectiveness in control of this nonnative grass. However, none have proven effective at the scale of the current invasion.
BILLING CODE 4310-55-P
EP05OC11.006
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In Texas and other portions of the pygmy-owl's range in the United States, such as semi-desert grasslands, invasive species and fire are not as significant in their impact because the vegetation communities in these areas are adapted to periodic fire. However, while fire may not be a primary issue, nonnative species can cause other effects to pygmy-owl habitat elements. For example, in Texas, studies indicate that the spread and prevalence of the nonnative grass,
Bothriochloa ischaemum
(King Ranch bluestem), results in this grass dominating native grasses, forbs, and endemic species, thus decreasing plant and animal species diversity and altering the vegetative structure of the community (Davis 2011, p. 4). It is not known if these changes in plant community structure affect pygmy-owls.
The best available scientific and commercial information, as presented in the discussion above, leads us to conclude that conversion of Sonoran
desertscrub to nonnative plant pastures composed of buffelgrass, and the subsequent change in the fire regime, has resulted in the loss of large areas of pygmy-owl habitat in the northern range of the pygmy-owl, is negatively impacting the remaining areas of pygmy-owl habitat in the Sonoran desert and tropical thornscrub/dry deciduous forest communities of Arizona, Sonora, and northern Sinaloa, and is expected to continue to do so in the foreseeable future. Other areas in Texas and the United States, such as semidesert grassland, are not as affected by buffelgrass and subsequent changes in fire behavior, but may be invaded by other nonnative species. However, the effect, if any, on pygmy-owls, has not been studied.
In contrast to the severity of buffelgrass invasion as a significant negative impact to the pygmy-owl in the northern portions of its range, it appears to have less impact or no impact at all further south. The area in Mexico that is susceptible to buffelgrass invasion and planting represents only just over 22 percent of the pygmy-owl's range. The magnitude of the impact diminishes in the southern portion of the range where buffelgrass has not been reported in the dry tropical forests, which comprise the majority of pygmy-owl habitat in the southern portion of its range. In addition, buffelgrass is not likely to invade and persist in these areas in the foreseeable future because it is adapted to dry, arid savannahs and grasslands in its native Africa (Burquez et al. 1998, p. 25). The elevational conditions, canopy coverage, and precipitation patterns of the dry tropical forest communities are not as suitable for the establishment of buffelgrass as the arid desert and semi-desert vegetation communities (Arriaga
et al.
2004, pp. 1508-1510.). The best available scientific and commercial information suggests that buffelgrass invasion should not be an issue in the southern portions of the pygmy-owls range, nor should it become an issue in the future.
Agricultural Production and Wood Harvesting
Agricultural development and wood harvesting can result in substantial impacts to the availability and connectivity of pygmy-owl habitat. Conversion of native vegetation communities to agricultural fields or pastures for grazing has occurred within historical pygmy-owl habitat in both the United States and Mexico, and not only removes existing pygmy-owl habitat elements, but also can affect the long-term ability of these areas to return to native vegetation communities once agricultural activities cease. Wood harvesting has a direct effect on the amount of available cover and nest sites for pygmy-owls and is often associated with agricultural development. Wood harvesting also occurs to supply firewood and charcoal, and to provide material for cultural and decorative wood carvings. While we do not have detailed information regarding the impacts of agricultural development and wood harvesting for all areas within the range of the pygmy-owl, the following provides a discussion of the extent of the impacts from these activities for areas for which we do have sufficient information.
The extent of agricultural development and woodcutting as a current or ongoing impact to pygmy-owl habitat differs between the United States and Mexico. For example, in the United States, habitat loss and conversion due to agricultural development is more of a historical issue because less area is being used currently for agriculture, and wood cutting is primarily for personal, rather than commercial use. However, impacts to pygmy-owl habitat from historical agricultural use and wood harvesting are still evident. The vegetation and soils of many valleys in the Sonoran Desert were shaped by the periodic flooding of dynamic wash systems, which partially recharged a shallow, fluctuating groundwater table. Because of agricultural development, these valleys no longer experience these defining processes and there has been a permanent loss of meso- and xero-riparian habitat (Jackson and Comus 1999, pp. 233, 249). These riparian habitats are important pygmy-owl habitat, especially within drier upland vegetation communities like Sonoran desertscrub and semi-desert grasslands.
In Arizona, although new agricultural development is limited and is expected to remain limited in the foreseeable future, the effects to historical habitat are still evident. Jackson and Comus (1999, pp. 249-250) describe the long-term effects of agricultural development on native vegetation communities, “The groundwater has been mined, river flows have been relocated, tributaries have been channelized, and smaller waterways are blocked by roads or the canals of the Central Arizona Project. Soil-surface characteristics have been greatly altered by field leveling and irrigation ditches. Compounding these large-scale changes, soil in some areas has increased salinity, pesticide residues, or loss of physical structure due to repeated tillage, soil compaction, and irrigation.” There have been important biological losses and introductions as well. Seed sources of native plants in these old agricultural fields are now rare. Natural regeneration of many of the old agricultural fields is unlikely because they are no longer near to a native seed source (Jackson and Comus 1999, pp. 243-247, 250).
It is not known to what extent the loss of certain pollinators, predators, detritivores (organisms that obtain nutrients by consuming decomposing organic matter), cryptogamic crusts (soil with crusts formed by an association of algae, mosses, and fungi; such crusts stabilize desert soil, retain moisture, and protect germinating seeds), mycorrhizae (a fungus that grows in a symbiotic association with plant roots), etc., as well as the addition of exotic species, will have on recovery of habitat. Because of these profound changes, we believe that habitat recovery, either by natural succession or through various attempts at ecological restoration, will be very limited (Jackson and Comus 1999, p. 250). The significance of this lies in the fact that many acres of pygmy-owl habitat have been lost to agricultural development, especially along valley bottoms and drainages that were important for pygmy-owls as they supported higher quality meso- and xero-riparian habitats. A well-known example of this is the huge mesquite bosque (woodland) south of Tucson on the San Xavier District of the Tohono O'odham Nation that comprised old-growth mesquites supporting cavities for pygmy-owl nests, adequate cover, and prey diversity, and which was lost due to groundwater pumping and diversion for agriculture and urban growth (Stromberg 1993, pp. 117-119). Mesquite bosques provide important pygmy-owl habitat. The viability of these bosques is dependent upon the ability of native trees, like mesquite, to reach the water table with their taproots. Only then can they grow to sizes that provide habitat for pygmy-owls. Even when abandoned and left to return to their natural state, there has been such extensive alteration of soils, drainage patterns, and contamination that these impacted bosques are unlikely to ever regain the historical habitat values. Restoration of old agricultural areas often meets with either limited success or failure.
Historically, agriculture in Sonora, Mexico, was restricted to small areas with shallow water tables, but it had, nonetheless, seriously affected riparian habitats by the end of the nineteenth century. Large-scale agriculture was introduced in the 1940s, with the construction of dams in the Rio Yaqui and Rio Mayo watersheds. By the late 1970s, the delta regions and alluvial
plains of these rivers were almost entirely converted to field crops. Huge expanses of natural vegetation had been cleared. The vast mesquite forests of the Llanos de San Juan Bautista in the plains of the Rio Sonora disappeared with the development of the Costa De Hermosillo irrigation district. In the Rio Mayo and Rio Yaqui coastal plains, nearly one million ha (2.5 million ac) of mesquite, cottonwood, and willow riparian forests and coastal thornscrub disappeared after dams upriver started to operate (Burquez and Martinez-Yrizar 2007, p. 543). In 1980, a national food system was initiated and the total area under cultivation in northern Mexico increased significantly (Stoleson
et al.
2005, p. 59).
Based upon the amount of area currently in irrigated agriculture, Sonora, with 530,000 ha (1.3 million ac), ranks second among the States in Mexico to Sinaloa (747,800 ha (1.85 million ac)), a State which is also occupied by pygmy-owls. The area equipped for agricultural irrigation in Sonora is 668,900 ha (1.65 million ac), resulting in the potential future loss of approximately 139,000 ha (343,000 ac) of natural vegetation communities (AQUASTAT 2007, p. 2) if these areas are developed for agriculture. Other Mexican States within the range of the pygmy-owl show similar potential for habitat loss. For example, in Tamaulipas, area under irrigation increased from 174,400 to 494,472 ha (431,000 to 1.22 million ac) between 1998 and 2004, with an area of 668,872 ha (1.65 million ac) equipped for irrigation. Michoacán supports 24,900 ha (61,500 ac) of irrigated lands with a potential infrastructure for 222,800 additional ha (550,600 ac). Although the amount of land converted to agriculture seems to be on the increase, we do not know where these areas are in relation to pygmy-owl habitat. Dry tropical forests on steeper slopes are not likely to be used for agricultural production. In addition, agricultural development in the States of Colima, Jalisco, Nayarit, and Nuevo Leon had substantial decreases in the amount of irrigated lands over the same period. Colima dropped from 64,100 ha (158,394 ac) to 37,800 ha (93,406 ac), Jalisco went from 161,600 ha (399,322 ac) to 95,600 ha (236,233 ac), Nayarit decreased from 55,400 ha (136,896 ac) to 43,200 ha (106,749 ac), and Nuevo Leon dropped from 143,000 ha (353,361 ac) to 32,484 ha (80,270 ac). These numbers indicate that continuing destruction of habitat for agricultural production is not occurring with the same intensity throughout the range of the pygmy-owl, and may be declining in large parts of its southern range (AQUASTAT 2007, p. 2).
Agricultural development is declining in some parts of the pygmy-owl's range, but seems concentrated in the northern portion of the range. In certain localities in northwestern Mexico, especially Sonora, it has remained the same and even increased over the past few decades. In the Sonoyta Valley of Sonora flanking Organ Pipe Cactus National Monument across the United States-Mexico border, cropland quadrupled in extent between 1977 and 1987, due in part to government-supported agricultural development. Proximity to U.S. fruit and vegetable markets, inexpensive labor, good quality water, and government agency interest in increased fruit and vegetable crops in the area mean that agricultural production and the associated descent of groundwater levels will likely continue in the future (Nabhan and Holdsworth 1998, p. 36). Some scientists surveyed noted that clearing for agriculture was becoming more severe in portions of the Lower Colorado River Valley, Central Gulf Coast, and Viscaino. Current Sonoran Desert cropland is most extensive in the border municipality of Mexicali and the extreme southern end of the Sonoran Desert where most municipalities have from one-quarter to three quarters of their land surface as cropland. The central section around Hermosillo, Sonora, is 15 to 25 percent cropland, and the rest of the area is less than 15 percent (Nabhan and Holdsworth 1998, p. 36). However, these figures do not include the millions of hectares (acres) of abandoned agricultural land. While not all the area converted for agriculture was or could be suitable pygmy-owl habitat, agricultural development has typically occurred along river bottoms and other drainages that support important riparian habitat for pygmy-owls (Flores-Villela and Fernandez 1989, p. 2). Additionally, associated habitat fragmentation exacerbates the actual impacts to available pygmy-owl habitat through loss of habitat connectivity (Stoleson et al. 2005, p. 60; Saunders et al. 1991, pp. 23-24).
Prescribed burning to reduce mesquite invasion into rangelands represents another potential threat to pygmy-owl habitat associated with agriculture. In general, improved grassland health adjacent to pygmy-owl habitat should benefit pygmy-owls through improved hydrology and enhance prey habitat. However, if woodlands providing important pygmy-owl habitat are not protected during prescribed burns, impacts to pygmy-owl habitat can be significant due to the loss of nest structures, predator and thermal cover, and prey habitat. For example, in Texas, two prescribed burns over the past 3 years have consumed 1,200 to 1,600 ha (3,000 to 4,000 ac) respectively, including areas that supported natural pygmy-owl nests, as well as pygmy-owl nest boxes (Proudfoot 2011b, p. 1). Other documented fires on the King Ranch consumed from several hundred up to 3,200 ha (8,000 ac) over this same time period (Caller 2009, NOAA 2011, Texas-Fire.com 2011, Firerescue 2008). While the loss of woodlands to fire is often a temporary impact, it can take many years for trees to reach adequate size to once again support cavities used for nesting by pygmy-owls.
Mesquite harvesting also has negative impacts on pygmy-owl habitat. Mesquite wood is a valuable commodity. Historically in Arizona, mesquite trees have been harvested for decades. In the late 1800s through the early 1900s, Arizona saw large-scale harvesting for fuel and for mining. Fuelwood cutting once had a major impact on the riparian forests, mesquite thickets, and evergreen woodlands near most of southeastern Arizona's major cities and mining centers (Bahre 1991, p. 143). This whole-scale harvest may explain the scarcity of riparian trees in early (1890) photographs of southern rivers such as the San Pedro (Stromberg 1993, p. 119). In the Sonoran Desert of Mexico, the mesquite tree is being harvested in order to fulfill the demand for mesquite charcoal, and former mesquite forests have disappeared at an alarming rate (Burquez and Martinez Yrizar 2007, p. 545). Ironwood trees are also being harvested in Mexico where the wood is cherished for its hardness and carving potential for native artwork by groups such as the Seri Indians.
Mesquite and ironwood woodlands provide pygmy-owl habitat elements related to tree canopy cover and a diverse prey base. Unfortunately, woodcutters and charcoal makers do not use scrubby-type mesquite, but rather take advantage of large, mature mesquite and ironwood trees growing in riparian areas (Taylor 2006, p. 12), the exact tree class that is of most value as pygmy-owl habitat. From the time “mesquite charcoal” became popular in U.S. restaurants in the early 1980s, both mesquite and ironwood have been harvested from the same lands, with as much as 15 to 40 percent of each mesquite charcoal bag consisting of ironwood prior to 1991. As a result, both trees were locally overexploited in Sonora and Baja California Sur (Taylor 2006, p. 12).
Sonora supports 1,888,000 ha (4,665,000 ac), or 46 percent of total mesquite woodlands in Mexico; more than double that of any other State in Mexico. This also means that much of the mesquite harvested in Mexico comes from Sonora (Taylor 2006, p. 12). Current estimates suggest that ironwood is being rapidly depleted across an area roughly equivalent to twice the size of Massachusetts. In northern Mexico, over 202,000 ha (500,000 ac) of mesquite have been cleared to meet the growing demand for mesquite charcoal (Haller 1994, p. 1). Haller (1994, p. 3) predicted that, if this trend continued, the entire ecosystem of the Sonoran Desert could crumble, and used the examples of the degraded ecosystem along the coast of Sonora near Kino Bay where most of the mesquite and ironwood had already been removed and virtually all plant and animal life has disappeared. Declining tree populations in the Sonoran Desert as a result of commercial uses and land conversion threatens other plant species, and may alter the structure and composition of the vertebrate and invertebrate communities as well (Bestelmeyer and Schooley 1999, p. 644). This has implications for pygmy-owl prey availability because pygmy-owls rely on a seasonal diversity of vertebrate and invertebrate prey species; loss of tree structure and diversity reduces prey diversity and availability.
In the Sonoyta region of Sonora, an area occupied by pygmy-owls, more than 193,000 ha (478,000 ac) have been affected by deforestation related to charcoal production, brick foundries, tourist crafts, and pasture conversion (Nabhan and Suzan 1994, p. 64). The accelerated rate of legume tree (trees belonging to the family
Leguminosae
whose characteristic fruit is a seed pod, including the mesquite and ironwood) depletion for charcoal and carvings in the Mexican States of Sonora and Baja California has clearly affected the health of ironwood populations and associated plant communities (Suzan
et al.
1997, p. 955). This is evidenced by an increased number of damaged and dying trees, as well as generally small size classes for sampled areas (Suzan
et al.
1997, pp. 950-955).
Pressure for fuelwood and crafts materials has been so intense in Mexico south of Organ Pipe Cactus National Monument that wood harvest, especially ironwood, has been detected more than 500 m (1600 ft) into the Monument as supplies have been depleted south of the border (Suzan
et al.
1999, p. 1499). The structure of both wash and upland habitats in the Monument have been affected by this harvest (Suzan
et al.
1999, p. 1499). Organ Pipe Cactus National Monument is one of four areas in Arizona that has been consistently occupied by pygmy-owls. In the arid environment of the Monument, tree canopy and structure are particularly important pygmy-owl habitat features.
Mesquite used as fuelwood is a thriving cross-border trade, although not on the same scale as charcoal. However, local impacts can be significant in the areas where the fuelwood is harvested. For example, Mexican trucks loaded with mesquite cross the border to Arizona at Sasabe. Interviews with these truck drivers indicated that most of the wood they haul comes from ejidos (communally owned lands) within a 20-km (12.4-mi) radius of the Town of Sasabe, an area occupied by nesting pygmy-owls (Taylor 2006, p. 5; Flesch 2008, p. 2).
In 2008, during field work in Sonora to gather pygmy-owl genetic samples, large areas of charcoal production were observed near Hermosillo. Impacts to vegetation were not limited to just the removal of the trees, but a significant area around the production sites was covered with fine, black charcoal dust covering all native vegetation (Service 2009, p. 1). The effects of these production areas are verified by reports of the complete removal of a dense mesquite bosque to the axe and charcoal pits just east of Hermosillo (Taylor 2006, p. 5). The immediate area around charcoal pits is often treeless. Walking transects away from charcoal pits revealed that all trees within a 1-km (0.6-mi) radius bear the scars of the chainsaw (Taylor 2006, p. 7).
Native woodlands in Sonora are additionally threatened as ranchers and charcoal producers team up to first clear the land of native trees for planting buffelgrass, and then use the dead trees to produce charcoal (Taylor 2006, pp. 6-7). The end result is the incentive to clear more native woodlands. Professional woodcutters are only permitted to harvest dead wood. However, dead wood to meet export demands is hard to come by. A simple solution practiced by many wood cutters is to ring trees and let them die; then the dead wood can be legally harvested (Taylor 2006, p. 7).
Impacts to pygmy-owl habitat in northwestern Mexico from these activities are resulting in the loss and fragmentation of habitat in this part of Mexico, and the inability to recover or restore habitats and habitat connectivity in Arizona. Impacts related to surface- and groundwater loss and channel diversions are long-term and are particularly significant as riparian habitat, both meso- and xero-riparian, are crucial for maintaining viable pygmy-owl populations in the arid portions of their range in Arizona and Sonora, Mexico. Loss of leguminous trees results in long-term effects to the soil as they add organic matter, fix nitrogen, and add sulfur and soluble salts, affecting overall habitat quality and quantity (Rodriguez Franco and Aguirre 1996, p. 6-47). Ironwood and mesquite trees are important nurse species for saguaros, the primary nesting substrate for pygmy-owls in the northern portion of their range (Burquez and Quintana 1994, p. 11). Demand for mesquite charcoal and firewood contributes to the loss of extensive, mature mesquite forests in riparian areas of northern Mexico.
The harvest of mature mesquites in the Sonoran Desert for charcoal and firewood permanently alters desert ecosystems because leguminous trees like mesquite and ironwoods are such important anchors for these systems and their associated flora and fauna (Taylor 2006, p. 8). Thus, ongoing wood harvesting can reduce or eliminate pygmy-owl habitat in the Sonoran Desert region of Arizona and Mexico by perpetuating scrubby trees that are unsuitable for nest substrates, supporting increased fire frequency associated with nonnative grass invasion, eliminating important nurse trees for saguaro protection, reducing tall canopy coverage important for pygmy-owl cover, and altering prey availability through the reduction of structural diversity.
Once common in areas of the Rio Grande delta, significant habitat loss and fragmentation due to woodcutting have now caused the pygmy-owl to be a rare occurrence in this area of Texas. Oberholser (1974, p. 452) concluded that agricultural expansion and subsequent loss of native woodland and thornscrub habitat, begun in the 1920's, preceded the rapid demise of pygmy-owl populations in the Lower Rio Grande Valley of southern Texas. Because much of the suitable pygmy-owl habitat in Texas occurs on private ranches, habitat areas are subject to potential impacts that are associated with ongoing ranch activities such as grazing, herd management, fencing, pasture improvements, construction of cattle pens and waters, road construction, and development of hunting facilities. Brush clearing, in particular, has been identified as a potential factor in present and future declines in the pygmy-owl population in Texas (Oberholser 1974, p. 452). However, relatively speaking, the current loss of habitat is much reduced
in comparison to the historic loss of habitat in Texas. Conversely, ranch practices that enhance or increase pygmy-owl habitat to support ecotourism can contribute to conservation of the pygmy-owl in Texas (Wauer
et al.
1993, p. 1076). The best available information does not indicate that current ranching practices are significantly affecting pygmy-owl habitat in Texas.
Tamaulipan brushland is a unique ecosystem that is found only in the Lower Rio Grande Valley of south Texas and northeastern Mexico. This vegetation community has historically supported occupancy by pygmy-owls. Brush clearing, pesticide use, and irrigation practices associated with agriculture have had detrimental effects on the Lower Rio Grande Valley (Jahrsdoerfer and Leslie 1988, p. 1). Since the 1920's, more than 95 percent of the original native brushland in the Lower Rio Grande Valley has been converted to agriculture or urban use. Along the Rio Grande River below Falcon Dam, 99 percent of the land has been cleared for agriculture and development. Cook
et al.
(2001, p. 3) indicated that both banks of the Rio Grande are now completely developed with homes or farms, and that the only remaining natural habitat areas south of the river are salt marshes and mudflats, both communities that are not used by pygmy-owls. A large percentage of similar habitat has been cleared in Mexico (Jahrsdoerfer and Leslie 1988, p. 17). This is supported by Tewes' (1992, p. 29) conclusion that most of the Rio Grande delta of Texas and Mexico has been developed over the past 60 years. Hunter (1988, p. 8) states, “Habitat removal in Mexico is widespread and nearly complete in northern Tamaulipas.”
Habitat fragmentation in northeastern Mexico is extensive, with only about two percent of the ecoregion remaining intact, and no habitat blocks larger than 250 square km (96.5 square mi), and no protected areas (Cook
et al.
2001, p. 4). This has the potential to limit pygmy-owl movements and dispersal, exacerbating the effects of small, isolated populations. Fire is often used to clear woodlands for agriculture in this area of Mexico, and many of these fires are not adequately controlled. There may be fire-related effects to native plant communities (Cook
et al.
2001, p. 4); however, there is no available information of how much area may be affected by this activity.
The best available scientific and commercial information indicates that historical land clearing, as a result of wood harvesting and agricultural development has caused the loss and alteration of a considerable area of pygmy-owl habitat in Arizona, Sonora, Texas, and northeastern Mexico. Past impacts continue to affect the extent of available pygmy-owl habitat in these areas, because of the extended time it takes for these lands to recover, even if negative actions cease, and impacts are expected to continue in many of these same areas into the foreseeable future. However, based on our review of the best available scientific and commercial information, we conclude that these impacts are limited in magnitude, because they are significant only in the northern portion of the range (Arizona, Texas, northwestern and northeastern Mexico). Moreover, the best available scientific and commercial data indicate that habitat loss due to woodcutting or agriculture is primarily historical in Texas, and these activities are not currently impacting habitats occupied by pygmy-owls on the private ranches in Texas. Further, the impacts in the southern portion of the range are less extensive, both because woodcutting and agricultural development appear to have less impact in the southern portion of the pygmy-owl's range, and because the pygmy-owl seems to be common throughout this area. Therefore, after reviewing and evaluating the best available scientific and commercial data, we conclude that woodcutting and agricultural development are not threats to the continued existence of the pygmy-owl rangewide, and are not likely to become so in the future.
Improper Livestock Grazing
Probably no single land use has had a greater effect on the vegetation of southeastern Arizona or has led to more changes in the landscape than improper livestock grazing and range-management programs (Carothers 1977, p. 4). Undoubtedly, grazing since the 1870s has led to soil erosion, destruction of those native plants most palatable to livestock, changes in the regional fire ecology, the spread of both native and alien plants, and changes in the age structure of evergreen woodlands and riparian forests (Bahre 1991, p. 123). Many areas of pygmy-owl habitat have recovered from these historical effects of grazing; however, other areas are slow to recover and may never recover due to the arid nature of the Sonoran Desert.
Livestock grazing in northwestern Mexico is probably the most widespread human use of Sonoran ecoregional landscapes. Grazing by cattle, goats, and other livestock has reduced vegetation cover and helped change grasslands to shrublands. Livestock grazing in the Sonoran Desert has fluctuated greatly in the last few centuries from being relatively confined and intensive to being extensive and intensive. In the 19th century, repeated Apache raids on ranchers and the paucity of water limited cattle production to relatively small areas (Bahre 1991, pp. 114-115). However, the late 19th century saw the largest stocking rates in history; extensive cattle production played a major role in the transformation of grasslands to scrublands, down-cutting of arroyos, the spread of nonnative plants, and degradation of riparian areas. Stocking rates are now much lower than in the 1890s because regulations such as those of the Taylor Grazing Act of 1934 helped improve rangeland quality in the United States. However, overstocking still continues in parts of northwestern Mexico, and Mexico's COTECOCA (Comisión Técnico Consultiva de Coeficientes de Agostadero) statistics confirm that 2 to 5 times the recommended stocking rates occur with regularity on the Sonoran side of the border (Walker and Pavlakovich Kochi 2003, p. 14; Nabhan and Holdsworth 1998, p. 2).
Available information on livestock grazing in Mexico that we evaluated was focused primarily on the border areas adjacent to the United States and in the arid areas of northwestern Mexico, such as Sonora. In Sonora, rangelands are often heavily grazed, with effects particularly apparent during drought (Rorabaugh 2008, p. 25). Sonora's higher stocking rate is likely due to its greater amounts of private and ejidal (communal) land, less regulation, and the greater dependence on ranching and farming in Mexico. Demand in North America drives the number of cattle in Sonora. The number of cattle in Sonora nearly doubled between 1950 and 1960. The Sonoran cattle population was 1,652,771 in 1990 according to official government statistics (Hawks 2003, p. 5). Other authors estimate the overstocking at 177 percent (Lopez 1992), with 60 to 400 percent overstocking in some areas (Burquez-Montijo
et al.
2002, p. 134). Excessive grazing of vegetation by livestock, especially when combined with conversion of plant cover to exotic pasture grasses, ranked as number four on a list of threats to the Sonoran Desert Ecoregion (Nabhan and Holdsworth 1998, p. 1).
One research study showed that overgrazing in Sonora leaves the Mexican landscape more exposed and, as a result, it dries out more rapidly following summer convective precipitation. After about 3 days, depletion of soil moisture evokes a period of higher surface and air
temperatures in northwestern Mexico (Bryant
et al.
1990, pp. 254-258). These drier soils and higher temperatures can result in impacts to vegetation survival and persistence. Effects of poorly managed livestock grazing in Sonora include changes in plant species composition and vegetation cover and structure, soil compaction, erosion, altered fire regimes, and nonnative plant species introductions and invasions (Stoleson
et al.
2005, pp. 61-62). With regard to pygmy-owl habitat, improper stocking rates can result in reduced saguaro reproduction through trampling and alteration of microclimates (Abouhaider 1989, pp. 40-48), reduced tree cover and reproduction through grazing of seedlings and seed pods, and impacts to prey availability from reduced vegetation structural diversity and species composition.
One of the most significant adverse impacts within western riparian systems has been the perpetuation of improper grazing practices. Belsky
et al.
(1999, p. 419) found that grazing by livestock has damaged 80 percent of the streams and riparian ecosystems in the arid regions of the western United States. The initial deterioration of western riparian systems began with the severe overgrazing in the late nineteenth century. Livestock grazing can affect four general components of riparian systems: (1) Streamside vegetation; (2) stream channel morphology; (3) shape and quality of the water column; and (4) structure of streambank soil. Vegetation impacts include: (1) Compaction of soil, which increases runoff and decreases water availability to plants; (2) herbage removal, which allows soil temperatures to rise, thereby increasing evaporation; (3) physical damage to vegetation by rubbing, trampling, and browsing; and (4) alteration of growth form of plants by removing terminal buds and stimulating lateral branching (Fleischner 1994, p. 635).
In a summary of studies investigating the impacts of livestock grazing on riparian areas, Belsky
et al.
(1999, p. 425) found that none of the studies showed positive impacts or ecological benefits that could be attributed to livestock activities when grazed areas were compared to protected areas. It was mostly negative effects that were reported, and there was little debate about those effects. Most of these studies tended to agree that improper livestock grazing can damage stream and riparian ecosystems. All types of riparian habitats provide important pygmy-owl habitat elements due to the increased size, diversity, and structure associated with riparian communities and enhanced moisture availability. Larger trees provide substrates for nest cavities. Structure diversity provides important predator and thermoregulatory cover, as well as an increased number and diversity of prey species. A reduction of the extent or quality of riparian habitats within the range of the pygmy-owl represents direct impacts on the availability and quality of pygmy-owl habitat.
Although proper management has greatly improved riparian communities in some areas, field data compiled in the last decade showed that riparian areas throughout much of the West were in the worst condition in history due mainly to the complications initiated by improper grazing techniques (Krueper 1993, p. 322). However, information submitted during the public comment period supports the idea that, in certain areas, riparian habitat has returned and, perhaps, even increased in certain areas in Arizona, including areas that are being grazed by livestock. Parker (2008, p. 13) points out that Webb
et al.
(2007, pp. 388-389, 404-408) conclude that, in the drainages they studied, increases in riparian vegetation from 24 percent to 49 percent had occurred since the late 1800s and early 1900s, and that increases in the density of riparian plants appear to have accelerated in the 1970s. We are encouraged by this positive information indicating that riparian habitats in some areas may become suitable for pygmy-owls in the future if grazing continues to be properly managed. It is not our contention that grazing per se has a negative effect on riparian areas, but that improper or overgrazing can have detrimental effects. Parker (2008, p. 14) reiterates this by stating, “While there is little question that overgrazing can degrade riparian ecosystems, the question here is whether grazing has had long-term negative effects on woody riparian vegetation in Arizona.” We acknowledge that, with proper management, riparian areas can recover and provide habitat for the pygmy-owl.
In Mexico, increasing human population numbers and the extent of subsistence agriculture threatens the future of Mexico's extensive riparian systems. Grazing impacts include contamination and an increasing demand for agricultural and forage production (Deloya 1985, pp. 9-11). Riparian destruction is evident throughout Mexico, but especially in areas of denser human population. Of particular relevance to the pygmy-owl has been the loss and destruction of virtually all of the dense woodlands within the Rio Grande River valley. Despite the evident destruction of riparian systems, little information exists on the problem and there is apparently no strategy at a national level to solve the problem. The present trends pose serious concerns for the future of Mexico's riparian ecosystems (Deloya 1985, pp. 11-12).
In Texas, areas occupied by pygmy-owls are primarily on large, private ranches where livestock production is a primary objective. However, alternative sources of revenue for these ranches also include hunting and ecotourism. As a result, habitat management for the benefit of wildlife is also a high priority for these ranchers. Livestock management is often conducted with consideration of impacts to wildlife.
Pygmy-owls are known to exist in areas that are grazed. Grazing, itself, does not appear to negatively affect pygmy-owls. Properly managed grazing can enhance certain pygmy-owl habitat elements (Loeser
et al.
2007, p. 96; Holechek
et al.
1982, p. 208). Climatic variation is important in determining the ecological effects of grazing practices in arid rangelands (Loeser
et al.
2007, pp. 93-96). However, improper grazing at inappropriate stocking rates or during seasons or years when drought and other conditions reduce forage availability can affect pygmy-owls directly through the loss of important habitat elements (e.g., saguaros, tree cover, riparian vegetation, vegetation reproduction) and prey availability. No studies specifically related to the effects of livestock grazing on pygmy-owls have been conducted; however, impacts to pygmy-owls can be determined indirectly from studies on related species or issues. For example, studies in Arizona and Sonora show that the number of lizard species and abundance of lizards declined significantly in heavily grazed areas (Jones 1981, p. 111); there is also a likely loss of lizard species in areas invaded by buffelgrass. Lizards are an important food resource for pygmy-owls; therefore, impacts to lizard abundance can affect pygmy-owls.
An additional concern related to grazing lands is that, faced with rising land prices, unstable markets, and unpredictable climate, many ranchers in the United States are choosing or are forced to sell their private lands to real estate developers or subdivide it themselves. This results in these lands being subject to the threats described above related to urbanization. There was no available information to determine if these same pressures apply to grazing lands in Mexico.
Improper livestock grazing has a negative impact on pygmy-owl habitat under some circumstances in Arizona and Sonora. While we expect that
continued implementation of improved grazing-management techniques will reduce grazing impacts on pygmy-owls in Arizona and Texas, we expected that overgrazing will continue to negatively impact pygmy-owls in Sonora and other parts of northern Mexico. Within the Sonoran desert, over grazing can result in loss of structural habitat components important to pygmy-owls, as well as reducing prey availability and diversity. Additionally, improper grazing during droughts can affect the long-term viability of riparian habitats, which are an important habitat type for pygmy-owls in Arizona and Sonora. However, there is no indication that livestock grazing precludes occupancy by pygmy-owls in any part of its range. While improper livestock grazing can have negative impacts to local pygmy-owl populations, we do not believe livestock grazing is significantly affecting pygmy-owl populations throughout its range. The best available scientific and commercial information does not appear to indicate that improper grazing is affecting pygmy-owl populations in Texas. We have no readily-available information to determine whether the effects of livestock grazing on pygmy-owl habitat in Mexico outside of Sonora are greater or more harmful than in Arizona and Sonora, but we suspect impacts are similar. Based on the best available scientific and commercial data, we conclude that improper livestock grazing is not a threat to the continued existence of the pygmy-owl rangewide, nor is it likely to become so.
Border Issues
One of the most pressing issues for the Arizona-Sonora border is the impact of illegal human and vehicular traffic through these unique and environmentally sensitive areas. Many of these locations now bear the scars of wildcat trails, abandoned refuse, and trampled vegetation (Marris 2006, p. 339; Walker and Pavlakovich-Kochi 2003, p. 15). Monitoring activities by the U.S. National Park Service (NPS) estimate that, annually, 300,000 individuals illegally cross through Organ Pipe Cactus National Monument in southwestern Arizona. Video surveillance equipment erected at Coronado National Memorial, in southeastern Arizona, indicates traffic volumes ranging from 100 to 150 immigrants per night (Walker and Pavlakovich-Kochi 2003, p. 15). In the Cabeza Prieta National Wildlife Refuge, located in southwestern Arizona, which supports resident pygmy-owls, there are over 640 km (400 mi) of illegal roads plus another 1,280 km (800 mi) of unauthorized foot trails as a result of illegal border activities (Cohn 2007, p. 96). These activities result in direct impacts to pygmy-owl habitat.
Additional information from the NPS indicates a significant issue “* * * is the increasing drug smuggling, illegal immigrants, and law enforcement activity which results in much greater human disturbance of the birds.” Further elaboration shows that the NPS believes “* * * that cactus ferruginous pygmy-owls within the Monument have been subject to repeated disturbance events and some habitat degraded as a result of long-term drought and impacts associated with illegal migration, drug smuggling, and law enforcement interdiction efforts” (Snyder 2005, pp. 1-3). Trails and roadways remove pygmy-owl habitat features, noise and disturbance from people and vehicles disrupt important behaviors, and there is an increased risk of fire in important habitats resulting from cooking and warming fires, as well as signal fires used by cross-border immigrants and smugglers. Areas occupied by pygmy-owls in Organ Pipe Cactus National Monument have been abandoned by the owls, likely due, at least in part, to heavy illegal immigrant traffic and associated enforcement actions.
There is fear that efforts to curb illegal border activities through the construction of infrastructure such as fences and barrier will fragment the Sonoran Desert ecosystem, damage the desert's plant and animal communities, and prevent free movement of wildlife between the United States and Mexico (Cohn 2007, p. 96). During the time the pygmy-owl was listed under the Act, we consulted on the effects of Federal border infrastructure projects and identified a number of potential impacts (Service 2003, pp. 66-85). The construction of new border infrastructure in the form of pedestrian fences, vehicle barriers, and patrol roads create impediments to pygmy-owl movement across the border due to pygmy-owl flight patterns and behavior (Marris 2006, p. 239; Vacariu 2005, p. 354). The fences and vehicle barriers, when considered in conjunction with patrol roads, drag roads, and vegetation removal, result in a combination of nonvegetated area with a raised structure in the middle causing an impediment to pygmy-owl movement, particularly given their normal flight patterns, where normal flights are generally less than 30 m (100 ft) and typically only 1.5 to 3.0 m (5 to 11 ft) above the ground (Flesch and Steidl 2007, p. 35; AGFD 2008b, p. 5). Flesch
et al.
(2009, pp. 7-9) show that the vegetation gaps, in association with the tall fences, may limit transboundary movements by pygmy-owls. Raptors are often attracted to artificial hunting perches, especially in areas that lack tall trees (Oles 2007, p. 1; Heintzelman 2004, p. 35; Askham 1990, p. 147). Border fences can provide open hunting areas and improved hunting perches for a variety of raptors that are potential predators of pygmy-owls. This combination of perches, open area, and an impediment to movement may result in increased predation of pygmy-owls, particularly dispersing juvenile pygmy-owls. Because the overall population of pygmy-owls likely functions as a metapopulation, the pygmy-owl depends on dispersal, emigration, and immigration to maintain the genetic and demographic fitness of regional populations. To the extent that border infrastructure and activities reduce or prevent such movements, and increase the likelihood of pygmy-owl predation, it follows that population-level impacts may result.
Impacts to pygmy-owls from border infrastructure and illegal activities are likely limited to the immediate border areas of Arizona and northern Sonora. Information was not readily available so that we could determine the extent of these impacts in Texas and northeastern Mexico, although they are likely to be similar (habitat gaps, perches for raptors,
etc.
). Nevertheless, these impacts are restricted to the border regions of Arizona and Texas, and only affect a relatively-small portion of the pygmy-owl range. This localized effect reduces the magnitude of this impact to the overall pygmy-owl population. Therefore, based on the best available scientific and commercial data, we conclude that effects associated with border activities are not a threat to the continued existence of the pygmy-owl rangewide, and are not likely to become so in the future.
Off-Highway Vehicle (OHV) Use
The information we have on impacts to the pygmy-owl from OHV use relates primarily to Arizona. Information was not readily available on any potential OHV impacts to pygmy-owls or pygmy-owl habitat in Texas and Mexico.
OHV use is widespread in Arizona and occurs on lands under a variety of management entities including the Forest Service, Bureau of Land Management, State Land Department, Tribes, and private individuals. The use of OHVs has grown considerably. For example, as of 2007, 385,000 OHVs were registered in Arizona (a 350 percent increase since 1998) and 1.7 million people (29 percent of Arizona's population) engaged in off-road activity from 2005 to 2007 (Sacco 2007). Over
half of OHV users reported that merely driving off the paved road was their primary activity, versus using the OHV for the purpose of seeking a destination to hunt, fish, or hike (Sacco 2007). Specific impacts to the pygmy-owl or its habitat from OHV use when driving off road include disturbance from noise and human activity, vegetation damage, changes in plant abundance and species composition, reduced habitat connectivity, soil compaction, soil erosion, reduced water infiltration, higher soil temperatures, destruction of cryptogamic soils (soil with crusts formed by an association of algae, mosses, and fungi; such crusts stabilize desert soil, retain moisture, and protect germinating seeds), and increased fire-starts (Boarman 2002, pp. 46-47; Ouren
et al.
2007, pp. 6-7, 11, 16).
Of specific concern is the regular use by OHV operators to utilize xero-riparian washes as travel ways. These washes provide important habitat elements for pygmy-owls due to the increased structure and productivity of vegetation resulting from the presence of increased moisture. Pygmy-owls use these wash areas for foraging, dispersal, thermal and predator cover, and for movements within their home range. Wash areas are often narrow and constrained, resulting in OHV impacts to vegetation and concentrated noise and disturbance, affecting the use and suitability of these areas as pygmy-owl habitat.
Pygmy-owls may be affected by OHV use in riparian areas. However, this effect is temporary and not continuous. Pygmy-owls may leave the area if disturbed by noise and return once the activity has ceased. Pygmy-owl habitat destruction in Arizona may result from OHV activity, but the magnitude and severity of this impact is relatively minor. Based on our evaluation of the best available scientific and commercial data, we conclude that OHV use does not threaten the continued existence of pygmy-owl, and is not likely to do so in the future.
Summary of Factor A
In summary, pygmy-owls require habitat elements such as mature woodlands that include appropriate cavities for nest sites, adequate structural diversity and cover, and a diverse prey base. A number of negative impacts described in Factor A are affecting pygmy-owl habitat within portions of its range. However, the best available scientific and commercial information indicates that most of these impacts are either restricted to or are greater in a smaller subset of the pygmy-owl's range (approximately 27 percent). For instance, we have detailed information that in the Arizona and Sonoran Desert Ecoregion, pygmy-owl habitat loss and fragmentation resulting from urbanization, changing fire regimes due to the invasion of buffelgrass, agricultural development and woodcutting, overgrazing, and border issues have had significant negative impacts on pygmy-owl habitat in these areas and will likely continue to do so to varying degrees in the foreseeable future. In Texas, which comprises approximately five percent of the pygmy-owl's range, historical loss of habitat has reduced the pygmy-owl range, but current impacts, such as livestock grazing and the invasion of nonnative plants, are reduced in their magnitude and severity.
For the larger part of the pygmy-owl's ranger in Mexico (the remaining 73 percent south of Sonora), the best available data indicates that many impacts to pygmy-owl habitat are reduced in their magnitude and severity or absent altogether. The rate of growth in these southern Mexican States is relatively slow compared with growth in Sonora and the Arizona border region and is expected to remain that way. Agricultural development has decreased in these areas, and buffelgrass is not a known threat to pygmy-owl habitat in this area and is not expected to become a threat in the future because of unfavorable growth conditions for buffelgrass. Historical loss of pygmy-owl habitat in northeastern Mexico has occurred, but there is no available evidence that significant habitat destruction is currently taking place. In addition, pygmy-owls are still considered common in the southern portion of their range. This information indicates that the negative impacts to pygmy-owl habitat discussed herein have different levels of effects on the populations of pygmy-owls throughout their range, and are much reduced or absent in the southern portion of the pygmy-owl's range. Based on the best available scientific and commercial information, we conclude that the present or threatened destruction, modification, or curtailment of its habitat or range is not a threat to the pygmy-owl rangewide now or in the foreseeable future.
Factor B: Overutilization for Commercial, Recreational, Scientific, or Educational Purposes
We are unaware of any overutilization of pygmy-owls for commercial, scientific, or educational purposes. However, the pygmy-owl is highly sought after by birders, who concentrate at several of the remaining known locations of pygmy-owls in the United States. For example, in 1996, a resident in Tucson reported a pygmy-owl sighting (documented pair) that subsequently was added to a local birding hotline, and the location was added to their website on the internet. Several carloads of birders were later observed in the area of the reported location (AGFD 1999, p. 12). As recently as 2003, property owners in Tucson have expressed concerns that birders and others have been documented trying to get photos or see pygmy-owls at occupied sites (AGFD 2003, p. 1).
In Texas, Tewes (1992, p. 28) states, “Frequent disruption by well-intentioned bird enthusiasts with call imitations may produce a local risk to the pygmy-owls, especially during breeding season.” We believe this disturbance problem is most significant in southern Texas. Oberholser (1974, p. 452) made a similar observation: “They [pygmy-owls] are considerably disturbed by hordes of bird watchers, some of whom keep their portable tape recorders hot for hours at a time in hopes that one of these rare birds will answer.” Recreational disturbance of pygmy-owls in Texas is particularly an issue in the side patches of mesquite, ebony, and cane in Starr and Hidalgo Counties (Oberholser 1974, p. 452). Oberholser (1974, p. 452) and Hunter (1988, p. 6) suggest that recreational birding may disturb pygmy-owls in highly visited areas, affecting their occurrence, behavior, and reproduction. Tewes (1992, p. 12) indicates that many amateur and professional ornithologists have strictly controlled or eliminated their use of taped calls to locate pygmy-owls because of the potential to affect the pygmy-owl's behavior.
Currently, a number of ranches in Texas offer the opportunity to view and photograph pygmy-owls. An internet search revealed invitations to birders to view pygmy-owls on the Canelo, King, and San Miguelito ranches. Additionally, both the AGFD and the Service continue to get requests to view and photograph pygmy-owls in Arizona.
Summary of Factor B
In summary, impacts to pygmy-owls from over-zealous birdwatchers have been documented in some areas within the range of the pygmy-owl. While pygmy-owls continue to be a highly sought after species by birders, there is some indication that compliance with etiquette related to use of tape-playback or call imitation has improved. We were unable to find any information on the effects of birding on pygmy-owls in Mexico, but we do not believe that it is a significant issue in Mexico, except
perhaps on local ranches or ejidos where ecotourism and bird watching are promoted. While the above impacts may negatively affect individual pygmy-owls on a local basis, landowners in areas that promote ecotourism are also likely to implement actions that have positive effects for the pygmy-owl. We conclude, based upon our review of the best commercial and scientific data available, that overutilization for commercial, recreational, scientific, or educational purposes is not a threat to the pygmy-owl now or likely to become so.
Factor C: Disease or Predation
Documentation of disease or predation as a significant mortality factor within a wildlife population requires extensive monitoring and the ability to observe individuals in hand. With regard to pygmy-owls, monitoring and capture has only occurred with any regularity in Arizona and Texas within the United States. This has included the capture of hundreds of individual pygmy-owls and subsequent monitoring using radio telemetry. Consequently, all of the available information on disease and predation is from Arizona and Texas. We are aware of only limited, anecdotal information related to predation for northwestern Mexico (Flesch 2010, pers. comm.). The following discussion outlines our evaluation of the information related to disease and predation that we have available from Arizona and Texas.
Little is known about the rate or causes of mortality in pygmy-owls; however, they are susceptible to predation from a wide variety of species. Recent research indicates that natural predation likely plays a key role in pygmy-owl population dynamics, particularly after fledging and during the postbreeding season (AGFD 2003, p. 2). AGFD telemetry monitoring in 2002 indicated at least three of the nine young produced that year were killed by predators prior to dispersal during a year when tree species failed to leaf out due to drought conditions (AGFD 2003, p. 2). Increased predation during a particularly harsh drought year (2004) in Arizona prompted a rescue effort by the AGFD and the Service during which two hatch-year pygmy-owls were temporarily brought into captivity to increase their chances of survival. They were subsequently released when habitat conditions improved (Service 2004, p. 1). Pygmy-owl predation by screech owls has been identified as a potential factor contributing to the decline of regional pygmy-owl population groups (AGFD 2008b, p. 9). However, there is not enough information to conclusively support this hypothesis. Predation is a significant pygmy-owl nest mortality factor associated with nest boxes and tree cavities in Texas. Proudfoot (2011a, p. 1) indicates that predation rates on natural cavities and unprotected nest boxes have been as high as 40 to 60 percent, with an average of 25 to 30 percent.
Domestic cat predation of pygmy-owls has been documented in both Texas and Arizona (AGFD 2003, p. 1; Proudfoot 1996, p. 79). Human population growth can increase the numbers of subsidized predators, such as household cats, that can affect pygmy-owl populations. As the number of potential predators increases, the chance of predation on pygmy-owls increases. In addition, domestic house cats consume considerable quantities of birds, reptiles, insects, and small mammals, reducing available pygmy-owl prey availability (Barratt 1995, p. 185; Coleman
et al.
1997, p. 2; Evans 1995, p. 4). This introduction of additional potential predators and a reduction in prey availability negatively affects pygmy-owls.
Ectoparasites have recently been identified as a potential threat to pygmy-owl populations (Proudfoot
et al.
2005, pp. 186-187; Proudfoot
et al.
2006c, pp. 874-875). These recent investigations in Texas and Arizona have indicated the regular occurrence of avian parasites in the materials inside of pygmy-owl nest cavities. The numbers of parasites may be high enough to affect nestling pygmy-owl health and survival. Blood parasites have been implicated in reduced body condition and impacts to survival and dispersal in small raptors (Dawson and Bortolotti 2000, pp. 3-5). Proudfoot
et al.
(2005, pp. 186-187) could not rule out that blood loss from external parasites, in combination with other factors, may have contributed to the loss of an entire clutch of pygmy-owls in Arizona.
The West Nile virus has been identified as the cause of a number of raptor mortalities throughout the United States, including Arizona. A number of North American owl species have documented mortality from West Nile virus, including the northern pygmy-owl (Gancz
et al.
2004, p. 2139). However, the West Nile virus has not been documented in cactus ferruginous pygmy-owls in either the United States or Mexico, and no pygmy-owl mortalities have been suspected to be the result of an infection with the West Nile virus.
Summary of Factor C
In summary, our review of the best available information suggests that disease and predation clearly have the potential to affect pygmy-owl individuals and populations, and have done so in local populations. However, information related to these factors is limited to pygmy-owl populations in the United States. We have only limited, anecdotal information related to predation on pygmy-owls in Mexico. Even in the United States, where predation has been documented, we conclude that it is not resulting in significant effects to the status of the pygmy-owl, because no disease or predation effects have been identified as having population-level effects on pygmy-owls. Based upon our review of the best commercial and scientific data available, we conclude that disease and predation are not threats to the pygmy-owl now or in the future.
Factor D: Inadequacy of Existing Regulatory Mechanisms
Regulations that could potentially address conservation of the pygmy-owl or pygmy-owl habitat in both the United States and Mexico may occur at a number of different levels of government, from Federal to local. The following discussion addresses the existing regulatory mechanisms related to the conservation of pygmy-owls and pygmy-owl habitat based on the best available information.
Although the pygmy-owl in Arizona is considered nonmigratory, it is protected under the Migratory Bird Treaty Act (MBTA) (16 U.S.C. 703-712). The MBTA prohibits “take” of any migratory bird; however, unlike take under the Endangered Species Act, some Federal courts have concluded that the MBTA does not apply to indirect forms of take such as habitat destruction, unless direct mortality or destruction of an active nest occurs during the activity that causes the habitat destruction
.
Other Federal and State regulations and policies, such as the Clean Water Act, the Department of Defense's Integrated Natural Resources Management Plans (Barry M. Goldwater Range) (Uken 2008, p.1), National Park Service policy, the inclusion of the pygmy-owl on the State of Arizona's list of Species of Special Concern (AGFD 1996, p. 15), and various municipal planning documents (Oro Valley 2008, p. 1) provide varying levels of protection, but have not been effective in protecting the pygmy-owl in Arizona from further decline. As a result of the implementation of the 2005 Real ID Act, the U.S. Department of Homeland
Security has waived application of the Endangered Species Act and other environmental laws in the construction of border infrastructure, including areas occupied by the pygmy-owl (73 FR 5271). Some local conservation mechanisms, such as habitat conservation plans, are in development in southern Arizona. These plans include conservation measures for pygmy-owls, but are at least a year from completion, and as drafts, do not afford the pygmy-owl any level of protection or conservation (although some pygmy-owl habitat has been conserved through acquisitions related to these plans). There are currently no statutory or regulatory provisions under Arizona law addressing the destruction or alteration of pygmy-owl habitat.
One member of the public provided information indicating that, because the current distribution of pygmy-owls occurs primarily on lands under Federal, State, or Tribal control, these lands are not at risk for the primary threats that have been identified (James 2008, p. 8). However, activities occur on all these lands that can result in all of the negative impacts to pygmy-owls identified in our 90-day finding and this document. None of these types of lands are immune to or restricted from impacts of facilities development, nonnative invasive species, changing fire regimes, drought, climate change, wood harvesting, bird watching, avian disease and predation, border issues, or any of the other impacts discussed above. In fact, it is on these very lands that many of these impacts, such as border issues, nonnative species invasions, fire, and recreation are concentrated. As discussed above, existing regulations governing these lands do not specifically protect pygmy-owls or their habitats, particularly absent protection under the Act.
A potential regulatory effect not specifically related to protection of the pygmy-owl, but which will affect our ability to conserve the pygmy-owl, has recently come to light with regard to Arizona State Trust lands. The Arizona State Land Department is considering restricting access to State Trust Lands for the purposes of conducting wildlife studies. Such access restrictions might prohibit further surveys, research, and monitoring of pygmy-owls on State Trust lands, due to new permit requirements and substantial cost. This has not been formally adopted and may be changed prior to finalization (Latimer 2010, p. 1). However, if implemented as described by Latimer (2010, p. 1), these proposed procedures and fees would likely limit pygmy-owl research on State Trust lands because of our and other biologists' inability to meet the requirements or pay the fees. This would have a substantial negative effect on our ability to conserve pygmy-owls within Arizona.
The State of Texas lists the pygmy-owl as threatened (TPWD 2009, p. 1). This designation requires permits for take of individuals for propagation, zoological gardens, aquariums, rehabilitation purposes, and scientific purposes (Texas Parks and Wildlife Code Chapters 67 and 68; Texas Administrative Code Sections 65.171-65.176, Title 31). There are no provisions for habitat protection. The pygmy-owl is also on the Texas Organization for Endangered Species (TOES) “watch list,” but this list provides no regulatory protection for the species or its habitat (TOES 1995, p. 1).
The establishment of protected areas of habitat and management to enhance or restore habitat are important to the conservation of pygmy-owl populations in both the United States and Mexico. In the United States, this could potentially be accomplished on lands managed by Federal agencies such as the Park Service, Bureau of Land Management, Department of Defense, and the Service. However, many of these lands have a multiple-use mandate and do not focus solely on pygmy-owl conservation, or even wildlife conservation in general. Similar issues exist in Mexico as well. Goals and objectives of wildlife management in Mexico have primarily focused on huntable or harvestable species.
A Mexican program to protect sensitive habitats and species is the National Natural Protected Areas (NPAs) system. NPA designation is supposed to protect areas that have not been significantly altered by human activities and that provide diverse ecosystem services. However, prior to 1994, most NPAs lacked sound and comprehensive management plans. By 2000, approximately 30 percent of new and existing NPAs had developed management plans. However, under the NPA model, these plans lacked detailed information, and in many cases could be considered obsolete. NPA goals to promote sustainable natural resources were often unattainable because of conflicting land ownership interests (Valdez
et al.
2006, p. 272). The allocation of funds for management of natural reserve areas in Sonora is precarious, and some reserves have not received protection other than that given by government edicts or their natural isolation (Burquez and Martinez-Yrizar 1997, p. 378). Urban development has taken its toll on Sonora's natural reserves. Three of the reserves have already disappeared, which reflects the tenuous state of many nature reserves in Mexico during the 1990s (Burquez and Martinez-Yrizar 2007, p. 546).
Another program set up to promote wildlife management on private property in Mexico is the development of wildlife management units, or UMAs. The UMA program in Mexico has not been effective in promoting wildlife management or biodiversity conservation. It has increased the introduction of exotic wildlife species to meet hunting demands. There is a lack of technical capability on private lands to conduct proper wildlife monitoring and management (Weber
et al.
2006, p. 1482). In Mexico, the exploitation of minerals and industrial development has not been matched by strong measures to protect the environment (Burquez and Martinez-Yrizar 2007, p. 547). Riparian management in particular seems to lack sufficient efforts (Kusler 1985, p. 6).
Summary of Factor D
In summary, Federal laws such as the Migratory Bird Treaty Act and Arizona and Texas State laws do address direct take of pygmy-owls within the United States. Existing regulations in Mexico d
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