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CFR Citation: 50 CFR Part 17

RIN ID: RIN 1018-AI49

NOTICE: Part II

DOCUMENT ACTION: Proposed rule.

SUBJECT CATEGORY: Endangered and Threatened Wildlife and Plants; Proposed Designation of Critical Habitat for Southwestern Willow Flycatcher (Empidonax traillii extimus)

DATES: We will accept comments until December 13, 2004. Public hearing requests must be received by November 26, 2004.

DOCUMENT SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to designate critical habitat for the federally endangered southwestern willow flycatcher (Empidonax trailli extimus) pursuant to the Endangered Species Act of 1973, as amended (Act). In developing this proposal, we evaluated those lands determined to be essential to the conservation of the southwestern willow flycatcher to ascertain if any specific areas are appropriate for exclusion from critical habitat pursuant to section 4(b)(2) of the Act. On the basis of our evaluation, we have determined that the benefits of excluding certain approved and pending Habitat Conservation Plans (HCPs) and lands owned and managed by the Department of Defense from critical habitat for the southwestern willow flycatcher outweighs the benefits of their inclusion, and have subsequently excluded those lands from this proposed designation of critical habitat for this species pursuant to section 4(b)(2) of the Act. As such, we propose to designate 376,095 acres (ac) (152,124 hectares (ha)) [including approximately 1,556 stream miles (2,508 stream kilometers)] of critical habitat which includes various stream segments and their associated riparian areas, not exceeding the 100 year floodplain or flood prone area, on a combination of Federal, State, Tribal, and private lands in southern California (CA), southern Nevada (NV), southwestern Utah (UT), southcentral Colorado (CO), Arizona (AZ), and New Mexico (NM).

We hereby solicit data and comments from the public on all aspects of this proposal, including data on economic and other potential impacts of the designation. We are also specifically soliciting public comments on the appropriateness of excluding lands covered by certain approved and pending HCPs and Department of Defense lands pursuant to section 4(b)(2) of the Act from this designation.

In the development of our final designation, we will incorporate or address any new information received during the public comment periods, or from our evaluation of the potential economic impacts of this proposal. As such, we may revise this proposal to address new information and/or to either exclude additional areas that may warrant exclusion pursuant to section 4(b)(2) or to add in those areas determined to be essential to the species but excluded from this proposal.

SUMMARY: Interior Department, Fish and Wildlife Service,

SUPPLEMENTAL INFORMATION

Some of the lands we have identified as essential for the conservation of the southwestern willow flycatcher are not being proposed as critical habitat. The following areas essential to the conservation of the southwestern willow flycatcher are not being proposed as critical habitat: ``missioncritical'' training areas on Marine Corps Base, Camp Pendleton (Camp Pendleton), and Seal Beach Naval Weapons Station, Fallbrook Detachment; areas within San Diego Multiple Species Conservation Program (MSCP); areas in the Draft Western Riverside Multiple Species Habitat Conservation Plan (MSHCP); and areas within the Draft City of Carlsbad Habitat Management Plan (MHCP). These areas have been excluded because we believe the benefit of excluding these areas from critical habitat outweighs the benefit of including them. We are also proposing to exclude areas covered under the Roosevelt Lake Habitat Conservation Plan from the final designation of critical habitat. We specifically solicit comment on the inclusion or exclusion of such areas and: (a) Whether these areas are essential; (b) whether these areas warrant exclusion; and (c) the basis for not designating these areas as critical habitat (section 4(b)(2) of the Act);

It is our intent that any final action resulting from this proposal will be as accurate as possible. Therefore, we solicit comments or suggestions from the public, other concerned governmental agencies, the scientific community, industry, or any other interested party concerning this proposed rule. Maps of proposed critical habitat are available for viewing by appointment during regular business hours at the AZ Ecological Services Office (see ADDRESSES section) or on the Internet at http://arizonaes.fws.gov. On the basis of public comment, during the development of the final rule we may find that areas proposed are not essential, are appropriate for exclusion under section 4(b)(2), or not appropriate for exclusion, and in all of these cases, this information would be incorporated into the final designation. Final management plans that address the conservation of the southwestern willow flycatcher must be submitted to us during the public comment period so that we can take them into consideration when making our final critical habitat determination. We particularly seek comments concerning:
(1) The reasons why any areas should or should not be determined to be critical habitat as provided by section 4 of the Act, including whether the benefits of designation will outweigh the benefits of excluding areas from the designation;
(2) Specific information on the distribution and abundance of southwestern willow flycatchers and their habitat, and which habitat or habitat components are essential to the conservation of this species and why;
(3) Comments or information as to whether further clarity or specificity of the Primary Constituent Elements is necessary; (4) Landuse designations and current or planned activities in or adjacent to the areas proposed and their possible impacts on proposed critical habitat;
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(5) Any foreseeable economic or other potential impacts resulting from the proposed designation, including, any impacts on small entities;
(6) Some of the lands we have identified as essential for the conservation of the southwestern willow flycatcher are being considered for exclusion from the final designation of critical habitat or are not included in this proposed designation. We specifically solicit comment on the possible inclusion or exclusion of such areas and:
(a) Whether these areas are essential;
(b) whether these, or other areas proposed but not specifically addressed in this proposal, warrant exclusion; and
(c) relevant factors that should be considered by us when evaluating the basis for not designating these areas as critical habitat under section 4(b)(2) of the Act); and
(7) This rule proposes to designate only lands currently occupied by the southwestern willow flycatcher; are there unoccupied lands that should be included and if so, the basis for such an inclusion; (8) Table 10 of the Southwestern Willow Flycatcher Recovery Plan (Chapter IV, page 86) provides a list of specific river reaches that the Technical Subgroup identified as having substantial recovery value and where recovery efforts should be focused. Are there river reaches identified within this list, not being proposed, but that should be considered for inclusion in the final designation of critical habitat and if so, the basis for such an inclusion;
(9) The focus of our proposal is to protect existing occupied habitat. We seek comment on the essential nature of also designating critical habitat in areas that are in proximity to existing breeding sites and the basis for such inclusion; and
(10) Whether our approach to designate critical habitat could be improved or modified in any way to provide for greater public participation and understanding, or to assist us in accommodating public concerns and comments.

If you wish to comment, you may submit your comments and materials concerning this proposal by any one of several methods. Please submit electronic comments in ASCII file format and avoid the use of special characters or any form of encryption. Please also include ``Attn: RIN 1018AI49'' in your email subject header and your name and return address in the body of your message. If you do not receive a confirmation from the system that we have received your Internet message, contact us directly by calling our AZ Ecological Services at 602/2420210. Please note that the email address,
wiflcomments@fws.gov, will be closed at the termination of the public comment period.

Our practice is to make comments, including names and addresses of respondents, available for public review during regular business hours. Individual respondents may request that we withhold their home addresses from the rulemaking record, which we will honor to the extent allowable by law. There also may be circumstances in which we would withhold from the rulemaking record a respondent's identity, as allowable by law. If you wish us to withhold your name and/or address, you must state this prominently at the beginning of your comments. However, we will not consider anonymous comments. We will make all submissions from organizations or businesses, and from individuals identifying themselves as representatives or officials of organizations or businesses, available for public inspection in their entirety. Comments and materials received will be available for public inspection, by appointment, during normal business hours at the above address.
Designation Of Critical Habitat Provides Little Additional Protection To Species

In 30 years of implementing the ESA, the Service has found that the designation of statutory critical habitat provides little additional protection to most listed species, while consuming significant amounts of conservation resources. The Service's present system for designating critical habitat is driven by litigation rather than biology, limits our ability to fully evaluate the science involved, consumes enormous agency resources, and imposes huge social and economic costs. The Service believes that additional agency discretion would allow our focus to return to those actions that provide the greatest benefit to the species most in need of protection.
Role of Critical Habitat in Actual Practice of Administering and Implementing the Act

While attention to and protection of habitat is paramount to successful conservation actions, we have consistently found that, in most circumstances, the designation of critical habitat is of little additional value for most listed species, yet it consumes large amounts of conservation resources. Sidle (1987) stated, ``Because the ESA can protect species with and without critical habitat designation, critical habitat designation may be redundant to the other consultation requirements of section 7.''

Currently, only 445 species, or 36 percent, of the 1,244 listed species in the (United States) U.S. under the jurisdiction of the Service have designated critical habitat. We address the habitat needs of all 1,244 listed species through conservation mechanisms such as listing, section 7 consultations, the section 4 recovery planning process, the section 9 protective prohibitions of unauthorized take, section 6 funding to the States, and the section 10 incidental take permit process. The Service believes that it is these measures that may make the difference between extinction and survival for many species.

We note, however, that a recent 9th Circuit judicial opinion, Gifford Pinchot Task Force v. United State Fish and Wildlife Service, has invalidated the Service's regulation defining destruction or adverse modification of critical habitat. We are currently reviewing the decision to determine what effect it may have on the outcome of consultations pursuant to section 7 of the Act.
Procedural and Resource Difficulties in Designating Critical Habitat

We have been inundated with lawsuits regarding critical habitat designation, and we face a growing number of lawsuits challenging critical habitat determinations once they are made. These lawsuits have subjected the Service to an everincreasing series of court orders and courtapproved settlement agreements, compliance with which now consumes nearly the entire listing program budget. This leaves the Service with little ability to prioritize its activities to direct scarce listing resources to the listing program actions with the most biologically urgent species conservation needs.

The consequence of the critical habitat litigation activity is that limited listing funds are used to defend active lawsuits and to comply with the growing number of adverse court orders. As a result, the Service's own proposals to undertake conservation actions based on biological priorities are significantly delayed.

The accelerated schedules of court ordered designations have left the Service with almost no ability to provide for meaningful additional public participation beyond those minimally required by the Administrative Procedures Act (APA), the Act, and the Service's implementing regulations, or to take additional time for review of comments and information to ensure the rule has addressed all the [[Page 60708]]
pertinent issues before making decisions on listing and critical habitat proposals, due to the risks associated with noncompliance with judicially imposed deadlines. This in turn fosters a second round of litigation in which those who will suffer adverse impacts from these decisions challenge them. The cycle of litigation appears endless, is very expensive, and in the final analysis provides little additional protection to listed species.

The costs resulting from the designation include legal costs, the cost of preparation and publication of the designation, the analysis of the economic effects and the cost of requesting and responding to public comment, and in some cases the costs of compliance with the National Environmental Policy Act (NEPA); all are part of the cost of critical habitat designation. These costs result in minimal benefits to the species that are not already afforded by the protections of the Act enumerated earlier, and they directly reduce the funds available for direct and tangible conservation actions.

Status and Distribution

The southwestern willow flycatcher (Empidonax traillii extimus) is a small passerine bird, approximately 15 centimeters (5.75 inches) in length. The southwestern willow flycatcher is one of four subspecies of the willow flycatcher currently recognized (Hubbard 1987; Unitt 1987), though Browning (1993) suggests a possible fifth subspecies (E. t. campestris) in the central and midwestern U.S. The willow flycatcher subspecies are distinguished primarily by subtle differences in color and morphology, and by habitat use. Phillips (1948) described the southwestern subspecies E. t. extimus, and most authors have accepted its taxonomic status (Aldrich 1951; Bailey and Niedrach 1965; Behle and Higgins 1959; Hubbard 1987, Phillips et al. 1964; Oberholser 1974; Monson and Phillips 1981; Unitt 1987; Schlorff 1990; Browning 1993; USFWS 1995). Recent research (Paxton 2000) concluded that E. t. extimus is genetically distinct from the other willow flycatcher subspecies. The southwestern willow flycatcher is generally paler than other willow flycatcher subspecies, and also differs in morphology (e.g., wing formula, bill length, and wing/tail ratio) (Unitt 1987 and 1997; Browning 1993). The willow flycatcher is an insectivore generalist (USFWS 2002: 26; Drost et al. 2003) taking a wide range of invertebrate prey including flying, and ground, and vegetationdwelling insect species of terrestrial and aquatic origins (Drost et al. 2003).

The historical breeding range of the southwestern willow flycatcher included southern CA, southern NV, southern UT, AZ, NM, western Texas, southwestern CO, and extreme northwestern Mexico (Hubbard 1987; Unitt 1987; Browning 1993). The flycatcher's current range is similar to the historical range, but the quantity of suitable habitat within that range is much reduced from historical levels (USFWS 2002: 710). At the end of 2002, 1,153 southwestern willow flycatcher territories were detected throughout southern CA, southern NV, southern UT, southern CO, AZ, and NM (Sogge et al. 2003). Rangewide totals do not exist yet for 2003, but the information that does exist from AZ (Smith et al. 2004) and NM (S.O. Williams, NMGFD, email 2004) indicates that rangewide numbers have not changed much in distribution or abundance. Since 2002, the southwestern willow flycatcher has not been recently detected breeding in western Texas (USFWS 2002: 9). Recent genetic work by Paxton (2000) verified southwestern willow flycatcher genetic stock in southcentral CO (i.e., San Luis Valley) and southwestern UT (e.g., Virgin River). The significance of this is that it confirms the northern extent of the range as E. t. extimus. Overall, Paxton (2000) showed that the northern boundary for southwestern willow flycatcher was generally consistent with that proposed by Unitt (1987) and Browning (1993). The current range described in the Recovery Plan (USFWS 2002: 8) adopts a range boundary that reflects these results.

The southwestern willow flycatcher is a neotropical migrant, spending time migrating and breeding in the U.S. from April into September. The flycatcher's wintering range includes southern Mexico, Central America, and probably South America (Stiles and Skutch 1989; Howell and Webb 1995; Ridgely and Gwynne 1989; Unitt 1997; Koronkiewicz et al. 1998; Unitt 1999). For an even more thorough discussion of the ecology, life history, and historical records of the southwestern willow flycatcher and most recent rangewide population estimates, see Chapter II of the Recovery Plan USFWS (2002) and Sogge et al. (2003).

The southwestern willow flycatcher currently breeds in relatively dense riparian habitats in all or parts of six southwestern states, from near sea level to over 2000 meters (m) (6100 feet (ft)) (USFWS 2002: D1). The southwestern willow flycatcher breeds in riparian habitats along rivers, streams, or other wetlands, where relatively dense growths of trees and shrubs are established, near or adjacent to surface water or underlain by saturated soil. Habitat characteristics such as dominant plant species, size and shape of habitat patch, canopy structure, vegetation height, and vegetation density vary widely among sites. Southwestern willow flycatchers nest in thickets of trees and shrubs ranging in height from 2 m to 30 m (6 to 98 ft). Lowerstature thickets (24 m or 613 ft tall) tend to be found at higher elevation sites, with tallstature habitats at middle and lower elevation riparian forests. Nest sites typically have dense foliage at least from the ground level up to approximately 4 m (13 ft) above ground, although dense foliage may exist only at the shrub level, or as a low dense canopy. Nest sites typically have a dense canopy. Some of the more common tree and shrub species currently known to comprise nesting habitat include Goodings willow (Salix gooddingii), coyote willow (Salix exigua) Geyers willow (Salix geyerana), arroyo willow (Salix lasiolepis), red willow (Salix laevigata), yewleaf willow (Salix taxifolia), boxelder (Acer negundo), tamarisk (aka saltcedar, Tamarix ramosissima), and Russian olive (Eleagnus angustifolia) (USFWS 2002: D 2). Generally, you would not find southwestern willow flycatchers nesting in an area without willows or tamarisk. A more detailed description of historical records by state and habitat characteristics (plant species, composition, structure, biotic vegetation
classification, patch size and shape, water and hydrological conditions, importance of the different stages of flycatcher habitat, etc.) can be found in the Recovery Plan (USFWS 2002: 719). The Recovery Plan is available on our website at http://arizonaes.fws.gov or by contacting the AZ Ecological Services Office (see ADDRESSES section).

Southwestern willow flycatchers are believed to exist and interact as groups of metapopulations (Noon and Farnsworth 2000; Lamberson et al. 2000; and USFWS 2002: 72). A metapopulation is a group of spatially disjunct local willow flycatcher populations connected to each other by immigration and emigration (USFWS 2002: 72). The distribution of the southwestern willow flycatcher varies geographically and is most stable where many connected sites and/or large populations exist (Coastal CA, Gila, Rio Grande Recovery Units) (Lamberson et al. 2000 and USFWS 2002: 72). A site may encompass a discrete breeding location, or several (USFWS 2002: 72). A territory is defined as a territorial or singing male detected during field
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surveys and generally equates to an area where both a male and female are present (Sogge et al. 1977). For more specific information on southwestern willow flycatcher presence/absence survey protocol, please see Sogge et al. (1997) and any subsequent updates at http://www.usgs.nau.edu/swwf. Metapopulation persistence or stability is more likely to increase by adding more sites rather than adding more territories to existing sites (Lamberson et al. 2000; USFWS 2002: 72; and USFWS 2003). This strategy distributes birds across a greater geographical range, minimizes risk of simultaneous catastrophic loss, and avoids genetic isolation (USFWS 2002: 72). In consideration of habitat that is dynamic and widely distributed, flycatcher metapopulation stability, population connectivity, and gene flow can be achieved through: Distributing birds throughout its range; having birds close enough to each other to allow for interaction; having large populations; having a matrix of smaller sites with high connectivity; and establishing habitat close to existing breeding sites, thereby increasing the chance of colonization (USFWS 2002: 75). As the population of a site increases, the potential to disperse and colonize increases; and an increase/decrease in one population affects other populations because populations are affected by the proximity, abundance, and reproductive productivity of neighboring populations (USFWS 2002: 75).

The breeding site and patch (a ``patch'' is defined as a discrete piece of southwestern willow flycatcher habitat) fidelity of adult, nestling, breeding, and nonbreeding southwestern willow flycatchers are just beginning to be understood (Kenwood and Paxton 2001; Koronkiewicz and Sogge 2001; USFWS 2002: 17). In central AZ at Roosevelt Lake (made up of a collection of ``sites''), from 1997 through 2000, 66 to 78 percent of southwestern willow flycatchers known to have survived from one breeding season to the next returned to the same breeding site; conversely, 22 to 34 percent of returning birds moved to different sites (Luff et al. 2000). A large percentage (75 percent) of known surviving 2000 adults returned in 2001 to their same breeding site (Kenwood and Paxton 2001). All, but three surviving birds out of 28, that were banded at Roosevelt Lake returned to Roosevelt Lake (Kenwood and Paxton 2001).

Southwestern willow flycatchers have higher site fidelity than nest fidelity and can move among sites within drainages and between drainages (Kenwood and Paxton 2001). Withindrainage movements are more common than betweendrainage movements (Kenwood and Paxton 2001). From nearly 300 band recoveries, withindrainage movements generally ranged from 1.6 to 29 kilometer (km) (1 to 18 miles (mi), but were as long as 40 km (25 mi) (E. Paxton, USGS, email). Movements of birds between drainages are more rare, and the distances are more varied. Banding studies have recorded 25 betweendrainage movements ranging from 40 km (25 mi) to a single movement of 443 km (275 mi) (average = 130 km or 81 mi) (E. Paxton, USGS, email). Movements have occurred from the Basin and Mohave Recovery Unit to the Lower Colorado Recovery Unit and from the Lower Colorado Recovery Unit to the Gila Recovery Unit.

As a neotropical migrant, migration stopover areas for the southwestern willow flycatcher, even though not used for breeding, may be critically important, (i.e., essential) resources affecting productivity and survival (Sogge et al. 1997b; Yong and Finch 1997; Johnson and O'Brien 1998; McKernan and Braden 1999; and USFWS 2002: E3 and 19). Use of riparian habitats along major drainages in the Southwest during migration has been documented (Sogge et al. 1997; Yong and Finch 1997; Johnson and O'Brien 1998; McKernan and Braden 1999; Koronkiewicz et al. 2003). Many of the willow flycatchers found migrating through riparian areas are detected in riparian habitats or patches that would be unsuitable for breeding (e.g., the vegetation structure is too short or sparse, or the patch is too small). On these drainages, migrating flycatchers use a variety of riparian habitats, including ones dominated by native or exotic plant species, or mixtures of both (USFWS 2002: E3). Willow flycatchers, like most small passerine birds, require foodrich stopover areas in order to replenish energy reserves and continue their northward or southward migration (Finch et al. 2000; USFWS 2002: E3 and 42).

The Recovery Plan for the southwestern willow flycatcher (USFWS 2002) was completed in 2002 and provides reasonable actions believed to be required to recover and protect the bird. The Recovery Plan (USFWS 2002: 105 to 136) provides the strategy for recovering the bird to threatened status and to the point where delisting is warranted. The Recovery Plan states that either one of two criteria can be met in order to downlist the species to threatened (USFWS 2002: 7778). The first relies on reaching a total population of 1,500 territories strategically distributed among all Recovery Units and maintained for three years with habitat protections (USFWS 2002: 7778). Habitat protections include a variety of options such as Habitat Conservation Plans, conservation easements, and Safe Harbor Agreements. The second criterion calls for reaching a population of 1,950 territories also strategically distributed among all Recovery and Management Units for five years without additional habitat protection (USFWS 2002: 7778). For delisting, the Recovery Plan recommends a minimum of 1,950 territories must be strategically distributed among all Recovery and Management Units, and these habitats must be protected from threats and create/secure sufficient habitat to assure maintenance of these populations and/or habitat for the foreseeable future through development and implementation of conservation management agreements (USFWS 2002: 7980). All of the delisting criteria must be accomplished and demonstrated their effectiveness for a period of 5 years (USFWS 2002: 7980).

Threats

The reasons for the decline of the southwestern willow flycatcher and current threats it faces are numerous, complex, and interrelated (USFWS 1995 and 2002: 33; Marshall and Stoleson 2000). However, these factors vary in severity over the landscape, and at any given locale, several are likely present, with cumulative and combined effects (USFWS 2002: 33).

The primary cause of the flycatcher's decline is loss and modification of habitat (USFWS 2002: 33). Historically, these habitats have always been dynamic (i.e. habitat size and location evolve over time), due to natural disturbance and regeneration events such as floods, fire, and drought (USFWS 2002: 3334). With increasing human populations and the related industrial, agricultural, and urban developments, these habitats have been further modified, reduced, and destroyed by various mechanisms (USFWS 2002: 34). Riparian ecosystems have declined from reductions in water flow, interruptions in natural hydrological events and cycles, physical modifications to streams, modification of native plant communities by invasion of exotic species, and direct removal of riparian vegetation (USFWS 2002: 34).

The major mechanisms causing loss and modification of riparian ecosystems, increases in exotic plant species, and quality of riparian habitat, are watermanagement and landuse practices such as dam operations, water
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diversion and groundwater pumping, river channelization and bank stabilization, control of phreatophytes (plants whose roots are associated with the water table), livestock grazing, recreation, fire, agricultural development, urbanization, and changes in the riparian plant communities. (USFWS 2002: 3342). Wintering habitat has also been lost and modified for this and other neotropical migratory birds (Finch 1991; Sherry and Holmes 1993) due to heavy agriculture uses and a decrease in lowland forest and wet areas (habitats in which southwestern willow flycatchers overwinter) (Koronkiewiez et al. 1998). A more detailed discussion of these threats can be found in the Recovery Plan (USFWS 2002: 3342).

In a review of historical and contemporary records and survey data of southwestern willow flycatchers throughout its range, Unitt (1987) noted that the species has ``declined precipitously'' and that ``the population is clearly much smaller now than 50 years ago.'' He believed the total was ``well under'' 1,000 pairs, more likely 500 (Unitt 1987). When the southwestern willow flycatcher was listed as endangered in 1995, approximately 350 territories were known to exist (Sogge et al. 2001). At the end of the 2002 breeding season, the minimum known number of southwestern willow flycatcher territories was 1,153 (455 in AZ, 238 in CA, 60 in CO, 344 in NM, 51 in NV, and 5 in UT) (Sogge et al. 2003). This number reflects the results of the most recent survey data. This also does not include flycatchers likely to occur on some Tribal and private lands. Though much suitable habitat remains to be surveyed, the rate of discovery of new nesting pairs at new locations has leveled off (Sogge et al. 2001). Unitt (1987) estimated that the total flycatcher population may be 500 to 1000 pairs; thus, nearly a decade of intense survey efforts have found little more than slightly above the upper end of Unitt's 1987 estimate (USFWS 2002: 29). Moreover, survey results reveal a consistent pattern range wide; the southwestern willow flycatcher population as a whole is comprised of extremely small, widely separated breeding groups or unmated flycatchers (74 percent of the breeding sites have five or fewer territories) (Sogge et al. 2003).

The 1,153 southwestern willow flycatcher territories are distributed in a large number of very small breeding groups, and only a small number of relatively large breeding groups (USFWS 2002: 41). These isolated breeding groups are vulnerable to local extirpation from floods, fire, severe weather, disease, and shifts in birth/death rates and sex ratios (USFWS 2002: 41). Marshall and Stoleson (2000) noted, ``Even moderate variation in stochastic (random) factors (such as floods or fires) that might be sustained by larger populations can reduce a small population below a threshold level from which it cannot recover. The persistence of small populations depends in part on immigration from nearby populations, at least in some years (Stacey and Taper 1992). The small, isolated nature of current southwestern willow flycatcher populations exacerbates the risk of local extirpation by reducing the likelihood of immigration among populations.'' The vulnerability of the few relatively large populations makes the above threats particularly acute (USFWS 2002: 41).

Previous Federal Actions

On January 25, 1992, a coalition of conservation organizations petitioned the Service, requesting listing of the southwestern willow flycatcher (E t. extimus) as an endangered species, under the Act. The petitioners also appealed for emergency listing, and designation of critical habitat. On September 1, 1992, we published a finding that the petition presented substantial information indicating that listing may be warranted and requested public comments and biological data on the species (57 FR 39664). On July 23, 1993, we published a proposal to list southwestern willow flycatcher as endangered with critical habitat (58 FR 39495), and again requested public comments and biological data on the species. We published a final rule to list southwestern willow flycatcher as endangered on February 27, 1995 (60 FR 10694). We deferred the final designation of critical habitat for this endangered species until July 23, 1995, pursuant to 16 U.S.C. 1533(b)(6)(C), citing issues identified in public comments, new information, and the lack of the economic information necessary to perform an economic analysis.

Following the final listing, we took no immediate action on the proposal to designate critical habitat due to a listing moratorium and a series of rescissions of listing funds imposed by Congress from April 1995 to April 1996. On March 20, 1997, the U.S. District Court of Arizona, in response to a suit by the (Southwest) Center for Biological Diversity, ordered us to designate critical habitat for the southwestern willow flycatcher within 120 days. On July 22, 1997, we published a final critical habitat designation for southwestern willow flycatcher along 964 river km (599 river mi) in AZ, CA, and NM (62 FR 39129) (USFWS 1997a). We published a correction notice on August 20, 1997, on the lateral extent of critical habitat (62 FR 44228) (USFWS 1997b).

As a result of a suit from the New Mexico Cattlegrower's Association initiated in March 1998, on May 11, 2001, the 10th Circuit Court of Appeals vacated (i.e., set aside) critical habitat, citing a faulty economic analysis, and instructed us to issue a new critical habitat designation. On September 30, 2003, in a complaint brought by the Center for Biological Diversity, the U.S. District Court of New Mexico instructed us to propose critical habitat by September 30, 2004, and publish a final rule by September 30, 2005. On January 21, 2004, we published a Notice of Intent to prepare an Environmental Assessment pursuant to NEPA and announced scoping meetings (69 FR 2940). We requested public comments on information about the flycatcher, management plans, and the scope of the environmental analysis, including alternatives that should be analyzed. We also held eight public scoping meetings in January and February, 2004, in Phoenix, AZ; Silver City and Albuquerque, NM; Alamosa, CO; Las Vegas, NV; and Lake Isabella, Chino, and Escondido, CA.

Critical Habitat

Section 3(5)(A) of the Act defines critical habitat as (i) the specific areas within the geographic area occupied by a species, at the time it is listed in accordance with the Act, on which are found those physical or biological features (I) essential to the conservation of the species and (II) that may require special management considerations or protection; and (ii) specific areas outside the geographic area occupied by a species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. ``Conservation'' means the use of all methods and procedures that are necessary to bring an endangered or a threatened species to the point at which listing under the Act is no longer necessary.

The designation of critical habitat does not affect land ownership or establish a refuge, wilderness, reserve, preserve, or other conservation area. It does not allow government or public access to private lands. Under section 7 of the Act, Federal agencies must consult with the Service on activities they undertake, fund, or permit that may affect critical habitat and lead to its destruction or adverse modification.
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However, the Act prohibits unauthorized take of listed species and requires consultation for activities that may affect them, including habitat alterations, regardless of whether critical habitat has been designated.

To be included in a critical habitat designation, habitat must be either a specific area within the geographic area occupied by the species on which are found those physical or biological features essential to the conservation of the species (primary constituent elements, as defined at 50 CFR 424.12(b)) and which may require special management considerations or protection, or be specific areas outside of the geographic area occupied by the species which are determined to be essential to the conservation of the species. Section 3(5)(c) of the Act states that not all areas that can be occupied by a species should be designated as critical habitat unless the Secretary determines that all such areas are essential to the conservation of the species. Our regulations (50 CFR 424.12(e)) also state that, ``The Secretary shall designate as critical habitat areas outside the geographic area presently occupied by the species only when a designation limited to its present range would be inadequate to ensure the conservation of the species.''

Regulations at 50 CFR 424.02(j) define special management considerations or protection to mean any methods or procedures useful in protecting the physical and biological features of the environment for the conservation of listed species. When we designate critical habitat, we may not have the information necessary to identify all areas that are essential for the conservation of the species. Nevertheless, we are required to designate those areas we consider to be essential, using the best information available to us. Accordingly, we do not designate critical habitat in areas outside the geographic area occupied by the species unless the best available scientific and commercial data demonstrate that unoccupied areas are essential for the conservation needs of the species.

Section 4(b)(2) of the Act requires that we take into consideration the economic impact, effects to national security, and any other relevant impact, of specifying any particular area as critical habitat. We may exclude areas from critical habitat designation when the benefits of exclusion outweigh the benefits of including the areas within critical habitat, provided the exclusion will not result in extinction of the species.

The Service's Policy on Information Standards Under the Endangered Species Act, published in the Federal Register on July 1, 1994 (59 FR 34271), and Section 515 of the Treasury and General Government Appropriations Act for Fiscal Year 2001 (Pub. L. 106554; H.R. 5658) and the associated Information Quality Guidelines issued by the Service, provide criteria, establish procedures, and provide guidance to ensure that decisions we make represent the best scientific and commercial data available. They require our biologists, to the extent consistent with the Act and with the use of the best scientific and commercial data available, to use primary and original sources of information as the basis for recommendations to designate critical habitat. When determining which areas are critical habitat, information may be obtained from the listing package, recovery plans, articles in peerreviewed journals, conservation plans developed by States and counties or other entities that develop HCPs, scientific status surveys and studies, and biological assessments. In the absence of published data unpublished materials and expert opinion or personal knowledge is used.

Areas that support populations, but are outside the critical habitat designation, are still important to the species. Because of that they will continue to be subject to conservation actions implemented under section 7(a)(1) of the Act and to the regulatory protections afforded by the section 7(a)(2) jeopardy standard, as determined on the basis of the best available information at the time of the action. Federally funded or permitted projects affecting listed species outside their designated critical habitat areas may still result in jeopardy findings in some cases. Similarly, critical habitat designations made on the basis of the best available information at the time of designation will not control the direction and substance of future recovery plans, habitat conservation plans, or other species conservation planning efforts if new information available to these planning efforts calls for different approaches.

Methods

In determining areas that are essential to conserve the southwestern willow flycatcher, we used the best scientific and commercial data available. We have reviewed the overall approach to the conservation of the southwestern willow flycatcher compiled in the Recovery Plan (USFWS 2002) and undertaken by local, State, Federal, and Tribal agencies, and private and nongovernmental organizations operating within the species' range since its listing in 1993.

We have also reviewed available information that pertains to the habitat requirements of this species. The material included data in reports submitted during section 7 consultations and by biologists holding section 10(a)(1)(A) recovery permits; research published in peerreviewed articles, agency reports, and databases; and regional Geographic Information System (GIS) coverages and habitat models.

A variety of sources were used to determine territory site information and locations. The Recovery Plan (USFWS 2002), the U.S. Geological Survey (USGS 2003) southwestern willow flycatcher rangewide database, and 2002 rangewide status report of the flycatcher (Sogge et al. 2003) were the most authoritative and complete sources of information. The database maintained by USGS, Colorado Plateau Research Station, Flagstaff, AZ (2003), compiles the results of surveys conducted throughout the bird's range. We had compiled 2003 data from AZ (Smith et al. 2004) and NM (S.O. Williams, NMGFD, email). AZ Game and Fish Department's Nongame Branch, in Phoenix, AZ, and SWCA, Inc. (Koronkiewicz et al. 2003; L. Dickerson, SWCA, Inc., email) generated migration data for AZ. A summary of known historical breeding records can be found in the Recovery Plan (USFWS 2002: 8 to 10). For more detailed information regarding the threats to the southwestern willow flycatcher and its habitat see the Recovery Plan (USFWS 2002: 33 to 42) and the listing rule (February 27, 1995; 60 FR 10694).

In the development of the proposal of critical habitat for the southwestern willow flycatcher, we determined which lands are essential to the conservation of the species by defining the physical and biological features essential to the species' conservation and delineating the specific areas defined by them. We then evaluated those lands determined to be essential to ascertain if any specific areas are appropriate for exclusion from critical habitat pursuant to section 4(b)(2) of the Act. On the basis of our evaluation, we have determined that the benefits of excluding certain approved and pending HCPs and lands owned and managed by the Department of Defense from critical habitat for the southwestern willow flycatcher outweighs the benefits of their inclusion, and have subsequently excluded those lands from this proposed designation of critical habitat for this subspecies pursuant to section 4(b)(2) of the Act (refer to ``Exclusions [[Page 60712]]
under Section 4(b)(2) of the Act'' section below). The resulting proposal includes a subset of lands essential to the conservation of the southwestern willow flycatcher.

Maps included with this proposal illustrate lands essential to the conservation of the southwestern willow flycatcher, with lands proposed as critical habitat and lands excluded from this proposal delineated separately. More detailed maps show lands determined to be essential to the species, which are color coded to clearly show those lands proposed and those excluded from this proposal, and are available from the AZ Ecological Services Office (see ADDRESSES section) or from the Internet at http://arizonaes.fws.gov. Primary Constituent Elements

In accordance with section 3(5)(A)(i) of the Act and regulations at 50 CFR 424.12, in determining which areas to propose as critical habitat, we consider those physical and biological features (primary constituent elements) that are essential to the conservation of the species and that may require special management considerations or protection. These features include but are not limited to: Space for individual and population growth and for normal behavior; food, water, air, light, minerals or other nutritional or physiological requirements; cover or shelter; sites for germination or seed dispersal; and habitats that are protected from disturbance or are representative of the historical, geographical, and ecological distributions of a species.

The areas proposed for designation as critical habitat are designed to provide sufficient riparian habitat for breeding, nonbreeding, territorial, dispersing, and migrating, southwestern willow flycatchers and to sustain southwestern willow flycatchers across their range. Although no areas are being proposed as critical habitat solely because they serve as a migration corridor, rather areas proposed serve a variety of functions that may include use by southwestern willow flycatchers as migration habitat. The habitat components essential for conservation of the species were determined from studies of southwestern willow flycatcher behavior and habitat use throughout the birds range (see ``Background'' section above). Due to the natural history of this neotropical migrant and the dynamic nature of the riparian environments in which they are found (USFWS 2002: Chapter II), one or more of the primary constituent elements described below are found throughout each of the units that are being proposed as critical habitat.

In general, all the constituent elements of critical habitat for the southwestern willow flycatcher are found in the riparian ecosystem within the 100year floodplain or flood prone area. Southwestern willow flycatchers use riparian habitat for feeding, sheltering, and cover while breeding and migrating. Because riparian vegetation is prone to periodic disturbance (e.g. flooding), flycatcher habitat is ephemeral and its distribution is dynamic in nature (USFWS 2002: 17). Flycatcher habitat may become unsuitable for breeding through maturation or disturbance, but suitable for migration or foraging (though this may be only temporary, and patches may cycle back into suitability for breeding) (USFWS 2002: 17). Therefore, it is not realistic to assume that any given breeding habitat patch will remain suitable over the longterm, or persist in the same location (USFWS 2002: 17). Over a fiveyear period, southwestern willow flycatcher habitat can, in optimum conditions, germinate, be used for migration or foraging, continue to grow, and eventually be used for nesting. Thus, habitat that is not currently suitable for nesting at a specific time, but useful for foraging and/or migration can be essential to the conservation of the flycatcher. Feeding sites and migration stopover areas are essential components of the flycatcher's survival, productivity, and health, and they can also be areas where new breeding habitat develops as nesting sites are lost or degraded (USFWS 2002: 42).

Based on our current knowledge of the life history and ecology of the southwestern willow flycatcher and the relationship of its essential life history functions to its habitat, as summarized in the ``Status and Threats'' sections above and in more detail in the Recovery Plan (USFWS 2002: Chapter II), it is important to recognize the combined nature of the primary constituent elements. Specifically, the relationships between river function, hydrology, floodplains, aquifers, and plant growth, form the environment essential to the conservation of the southwestern willow flycatcher.

The natural hydrologic regime and supply of (and interaction between) surface and subsurface water will be a driving factor in the maintenance, growth, recycling, and regeneration of southwestern willow flycatcher habitat (USFWS 2002: 16). As streams reach the lowlands, their gradients typically flatten and surrounding terrain open into broader floodplains (USFWS 2002: 32). Combine this setting with the integrity of stream flow frequency, magnitude, duration, and timing (Poff et al. 1997), and conditions will occur that provide for proper river channel configuration, sediment deposition, periodic inundation, recharged aquifers, lateral channel movement, and elevated groundwater tables throughout the floodplain that develop flycatcher habitat (USFWS 2002: 16). Maintaining existing river access to the floodplain when overbank flooding occurs is integral to allow deposition of fine moist soils, water, nutrients, and seeds that provide essential material for plant germination and growth. An abundance and distribution of fine sediments extending farther laterally across the floodplain and deeper underneath the surface retains much more subsurface water, which in turn supplies water for the development of flycatcher habitat and microhabitat conditions (USFWS 2002: 16). The interconnected interaction between groundwater and surface water contributes to the quality of riparian community (structure and plant species), and will influence the germination, density, vigor, composition, and ability to regenerate and maintain itself (AZ Department of Water Resources 1994).

The specific biological and physical features, otherwise referred to as the primary constituent elements, essential to the conservation of the southwestern willow flycatcher are:
(1) Nesting habitat with trees and shrubs that include, but are not limited to, willow species and boxelder;
(2) Dense riparian vegetation with thickets of trees and shrubs ranging in height from 2 m to 30 m (6 to 98 ft) with lowerstature thickets of (24 m or 613 ft tall) found at higher elevation riparian forests and tallstature thickets at found at middle and lower elevation riparian forests;
(3) Areas of dense riparian foliage at least from the ground level up to approximately 4 m (13 ft) above ground or dense foliage only at the shrub level, or as a low, dense tree canopy;
(4) Sites for nesting that contain a dense tree and/or shrub canopy (the amount of cover provided by tree and shrub branches measured from the ground) (i.e. a tree or shrub canopy with densities ranging from 50 percent to 100 percent);
(5) Dense patches of riparian forests that are interspersed with small openings of open water or marsh or shorter/sparser vegetation, that creates a mosaic that is not uniformly dense. Patch size may be as small as 0.1 ha (0.25 ac) or as large as 70 ha (175 ac); and [[Page 60713]]
(6) A variety of insect prey populations, including but not limited to, wasps and bees (Hymenoptera); flies (Diptera); beetles (Coleoptera); butterflies/moths and caterpillars (Lepidoptera); and spittlebugs (Homoptera).

A description of the essential environment as it relates to the specific primary constituent elements required of the southwestern willow flycatcher is described below.
Space for Individual and Population Growth and Normal Behavior

Streams of lower gradient and/or more open valleys with a wide/ broad floodplain are the geological settings that support willow flycatcher breeding habitat from near sea level to over 2000 m (6100 ft) in southern CA, southern NV, southern UT, southern CO, AZ, and NM (USFWS 2002: 7). Lands with moist conditions which support riparian plant communities are areas that provide habitat for the southwestern willow flycatcher. Conditions like these develop in lower floodplains as well as where streams enter impoundments, either natural (e.g., beaver ponds) or humanmade (reservoirs). Lowgradient stream conditions may also occur high in watersheds, as in the marshy mountain meadows supporting flycatchers in the headwaters of the Little Colorado River near Greer, AZ, or the flatgradient portions of the upper Rio Grande in southcentral CO and northern NM (USFWS 2002: 32). Sometimes, the lowgradient wider floodplain exists only at the habitat patch itself, on streams that are generally steeper when viewed on the large scale (e.g., percent gradient over kilometers or miles) (USFWS 2002).

Relatively steep, confined streams can also support flycatcher habitats (USFWS 2002: D13). The San Luis Rey River in CA supports a substantial flycatcher population, and stands out among flycatcher habitats as having a relatively high gradient and being confined in a fairly narrow, steepsided valley (USFWS 2002: D13). It is important to note that even a steep, confined canyon or mountain stream may present local conditions where just a portion of an acre (ac) or hectare (ha) of flycatcher habitat may develop (USFWS 2002; D13). Such sites are important individually, and in aggregate (USFWS 2002: D13). Flycatchers are known to occupy very small, isolated habitat patches, and may occur in fairly high densities within those patches. Water

Flycatcher nesting habitat is largely associated with perennial or persistent stream flow that can support the expanse of vegetation characteristics needed by the flycatcher, but can persist on intermittent or ephemeral streams that retain local conditions favorable to riparian vegetation (USFWS 2002: D12). The range and variety of stream flow conditions (frequency, magnitude, duration, and timing) (Poff et al. 1997) that will establish and maintain flycatcher habitat can arise in different types of both regulated and unregulated flow regimes throughout its range (USFWS 2002: D12). Also, flow conditions that will establish and maintain flycatcher habitat can be achieved in regulated streams, depending on scale of operation and the interaction of the primary physical characteristics of the landscape (USFWS 2002: D12).

In the southwest, natural hydrological conditions at a flycatcher breeding site can vary remarkably within a season and between years (USFWS 2002: D12). At some locations, particularly during drier years, water or saturated soil is only present early in the breeding season (i.e., May and part of June) (USFWS 2002: D12). At other sites, vegetation may be immersed in standing water during a wet year, but be hundreds of meters from surface water in dry years (USFWS 2002: D12). This is particularly true of reservoir sites such as the Kern River at Lake Isabella, CA, Tonto Creek and Salt River at Roosevelt Lake, AZ, and the Rio Grande near Elephant Butte Reservoir, NM (USFWS 2002: D 12). Similarly, where a river channel has changed naturally (Sferra et al. 1997), there may be a total absence of water or visibly saturated soil for several years. In such cases, the riparian vegetation and any flycatchers breeding within it may persist for several years (USFWS 2002: D12).

In some areas, natural or managed hydrologic cycles can create temporary flycatcher habitat, but may not be able to support it for an extended amount of time, or may support varying amounts of habitat at different points in the cycle. Some dam operations create varied situations that allow different plant species to thrive when water is released below a dam, held in a lake, or removed from a lakebed, and consequently, varying degrees of flycatcher habitat are available as a result of dam operations (USFWS 2002: 33).

The riparian vegetation that constitutes southwestern willow flycatcher breeding habitat requires substantial water (USFWS 2002: D 12). Because southwestern willow flycatcher breeding habitat is often where there is slow moving or still water we speculate these slow and still water conditions may also be important in influencing the production of insect prey base for flycatcher food (USFWS 2002: D12) Sites for Germination or Seed Dispersal

Subsurface hydrologic conditions may, in some places (particularly at the more arid locations of the southwest), be equally important to surface water conditions in determining riparian vegetation patterns (Lichivar and Wakely 2004). Where groundwater levels are elevated to the point that riparian forest plants can directly access those waters it can be an area essential for nesting, foraging, migrating, nonbreeding, dispersing, or unmated southwestern willow flycatchers, and we speculate that these elevated groundwaters help create moist soil conditions believed to be important for microhabitat nesting conditions and prey populations (USFWS 2002: 11).

Depth to groundwater plays an important part in the distribution of riparian vegetation (AZ Department of Water Resources 1994) and consequently, southwestern willow flycatcher habitat. The greater the depth to groundwater below the land surface, the less abundant the riparian vegetation (AZ Department of Water Resources 1994). Localized perched aquifers (i.e. a saturated area that sits above the main water table) can and do support some riparian habitat, but these systems are not extensive (AZ Department of Water Resources 1994).

The abundance and distribution of fine sediment deposited on floodplains is critical for the development, abundance, distribution, maintenance, and germination of flycatcher habitat, and possibly conditions for successful breeding (USFWS 2002: 16). In almost all cases, moist or saturated soil is present at or near breeding sites during wet or nondrought years (USFWS 2002: 11). Thus, fine sediments provide seeds beds for flycatcher habitat. The saturated soil and adjacent surface water may be present early in the breeding season, but only damp soil is present by late June or early July (Muiznieks et al. 1994; USFWS 2002: D3). Microhabitat features such as temperature and humidity, facilitated by moist/saturated soil, are believed to play an important role where flycatchers are detected and nest, their breeding success, and availability/abundance of food resources (USFWS 2002). However, as in all natural systems the amount and duration of flooding is dependent on natural cycles.
[[Page 60714]]

Reproduction and Rearing of Offspring

Southwestern willow flycatchers nest in thickets of trees and shrubs ranging in height from 2 m to 30 m (6 to 98 ft) (USFWS 2002: D 3). Lowerstature thickets (24 m or 613 ft tall) tend to be found at higher elevation sites, with tallstature habitats at middle and lowerelevation riparian forests (USFWS 2002: D2). Nest sites typically have dense foliage at least from the ground level up to approximately 4 m (13 ft) above ground, although dense foliage may exist only at the shrub level, or as a low, dense tree canopy (USFWS 2002: D3).

Riparian habitat characteristics such as dominant plant species, size and shape of habitat patches, tree canopy structure, vegetation height, and vegetation density vary widely among sites, but are essential qualities of southwestern willow flycatcher breeding habitat (USFWS 2002: D1). The accumulating knowledge of flycatcher breeding sites reveals important areas of similarity which constitute the basic concept of what is suitable breeding habitat (USFWS 2002: D2). These habitat features are generally discussed below.

Regardless of the plant species composition or height, occupied breeding sites usually consist of dense vegetation in the patch interior, or an aggregate of dense patches interspersed with openings (USFWS 2002: 11). In most cases this dense vegetation occurs within the first 34 m (1013 ft) above ground (USFWS 2002: 11). These dense patches are often interspersed with small openings, open water or marsh, or shorter/sparser vegetation, creating a mosaic that is not uniformly dense (USFWS 2002: 11).

Common tree and shrub species currently known to comprise nesting habitat include willow species, boxelder, tamarisk, and Russian olive (USFWS 2002: D2, 11). Other plant species used for nesting have been buttonbush (Cephalanthus occidentalis), cottonwood, stinging nettle (Urtica dioica), alder (Alnus rhombifolia, Alnus oblongifolia, Alnus tenuifolia), velvet ash (Fraxinus velutina), poison hemlock (Conium maculatum), blackberry (Rubus ursinus), seep willow (Baccharis salicifolia, Baccharis glutinosa), oak (Quercus agrifolia, Quercus chrysolepis), rose (Rosa californica, Rosa arizonica, Rosa multiflora), sycamore (Platinus wrightii), giant reed (Arundo donax), false indigo (Amorpha californica), Pacific poison ivy (Toxicodendron diversilobum), grape (Vitus arizonica), Virginia creeper (Parthenocissus
quinquefolia), Siberian elm (Ulmus pumila), and walnut (Juglans hindsii) (USFWS 2002: D3, 5, and 9). Other species used by nesting southwestern willow flycatchers may become known over time as more studies and surveys occur.

Nest sites typically have a dense tree and/or shrub canopy (USFWS 2002: D3). Canopy density (the amount of cover provided by tree and shrub branches measured from the ground) at various nest sites ranged from 50 percent to 100 percent.

Southwestern willow flycatcher breeding habitat can be generally organized into three broad habitat typesthose dominated by native vegetation, by exotic vegetation, and those with mixed native and exotic plants. These broad habitat descriptors reflect the fact that southwestern willow flycatchers now inhabit riparian habitats dominated by both native and nonnative plant species.

The riparian patches used by breeding flycatchers vary in size and shape (USFWS 2002: D2). They may be relatively dense, linear, contiguous stands or irregularlyshaped mosaics of dense vegetation with open areas (USFWS 2002: D2 and 11). Southwestern willow flycatchers have been recorded nesting in patches as small as 0.1 ha (0.25 ac) along the Rio Grande (Cooper 1997), and as large as 70 ha (175 ac) in the upper Gila River in NM (Cooper 1997). The mean reported size of flycatcher breeding patches was 8.6 ha (21.2 ac). The majority of sites were toward the smaller end, as evidenced by a median patch size of 1.8 ha (4.4 ac) (USFWS 2002: 17). Mean patch size of breeding sites supporting 10 or more flycatcher territories was 24.9 ha (62.2 ac). Aggregations of occupied patches within a breeding site may create a riparian mosaic as large as 200 ha (494 ac) or more, such as at the Kern River (Whitfield 2002), Roosevelt Lake (Paradzick et al. 1999) and Lake Mead (McKernan 1997). Based on the number of flycatcher territories reported in each patch, it required an average of 1.1 ha (2.7 ac) of dense riparian habitat for each territory in the patch (USFWS 2002: 81, D11). Because breeding patches include areas that are not actively defended as territories, this does not equate to an average territory size.

Flycatchers often cluster their territories into small portions of riparian sites (Whitfield and Enos 1996; Paxton et al. 1997; Sferra et al. 1997; Sogge et al. 1997), and major portions of the site may be occupied irregularly or not at all. Recent habitat modeling based on remote sensing and GIS data has found that breeding site occupancy at reservoir sites in AZ is influenced by vegetation characteristics of habitat adjacent to the actual occupied portion of a breeding site (Hatten and Paradzick 2003); therefore, areas adjacent to breeding sites can be an important component of a breeding site. How size and shape of riparian patches relate to factors such as flycatcher site selection and fidelity, reproductive success, predation, and brood parasitism is unknown (USFWS 2002: D11).

Flycatchers are generally not found nesting in confined floodplains (i.e. those bound within a canyon) (Hatten and Paradzick 2003) or where only a single narrow strip of riparian vegetation less than approximately 10 m (33 ft) wide develops (USFWS 2002: D11). While riparian vegetation too mature, immature, or of lesser quality in abundance and breadth may not be used for nesting, it can be used by breeders for foraging (especially if it extends out from larger patches) or during migration for foraging, cover, and shelter (Sogge and Tibbitts 1994; Sogge and Marshall 2000).

Food

We speculate that willow flycatcher food availability may be largely influenced by the density and species of vegetation, proximity to and presence of water, saturated soil levels, and microclimate features such as temperature and humidity (USFWS 2002). Flycatchers forage within and above the canopy, along the patch edge, in openings within the territory, over water, and from tall trees as well as herbaceous ground cover (Bent 1960; McCabe 1991). Willow flycatchers employ a ``sit and wait'' foraging tactic, with foraging bouts interspersed with longer periods of perching (Prescott and Middleton 1988). The willow flycatcher is somewhat of an insect generalist (USFWS 2002: 26), taking a wide range of invertebrate prey including flying, and ground, and vegetationdwelling species of terrestrial and aquatic origins (Drost et al. 2003). Wasps and bees (Hymenoptera) are common food items, as are flies (Diptera), beetles (Coleoptera), butterflies/ moths and caterpillars (Lepidoptera), and spittlebugs (Homoptera) (Beal 1912; McCabe 1991). Plant foods such as small fruits have been reported (Beal 1912; Roberts 1932; Imhof 1962), but are not a significant food during the breeding season (McCabe 1991). Diet studies of adult southwestern willow flycatchers (Drost et al. 1997; DeLay et al. 1999) found a wide range of prey taken. Major prey items were small (flying ants) to large (dragonflies) flying insects, with
[[Page 60715]]
Hymenoptera, Diptera, and Hemiptera (true bugs) comprising half of the prey items. Willow flycatchers also took nonflying species, particularly Lepidoptera larvae. From an analysis of southwestern willow flycatcher diet along the South Fork of the Kern River, CA (Drost et al. 2003), flycatchers consumed a variety of prey from 12 different insect groups. Willow flycatchers have been identified targeting seasonal hatchings of aquatic insects along the Salt River arm of Roosevelt Lake, AZ (E. Paxton, USGS, email).

Primary Constituent Elements Summary

The discussion above outlines those physical and biological features essential to the southwestern willow flycatcher and presents our rationale as to why those features were selected. The primary constituent elements described above include the essential features of the dynamic riverine environment that germinates, develops, maintains, and regenerates the necessary riparian forest and provides food for nesting, foraging, nonbreeding, unmated, and migrating southwestern willow flycatchers. These habitat features are essential for the flycatcher to maintain metapopulation stability, connectivity, gene flow, and protect against catastrophic loss for disjunct populations distributed across a large geo

FOR FURTHER INFORMATION CONTACT Steve Spangle, Field Supervisor, AZ Ecological Services Office (telephone 602/2420210; facsimile 602/242 2513).