Impact of Climate Change and Land Use on the Southwestern United States

Impacts of climate change on life and ecosystems

Potential Impacts of Global Climate Change on Bird Communities of the Southwest

Charles van Riper III, Mark K. Sogge, and David W. Willey
Biological Resources Division
U.S. Geological Survey

The narrow strips of riparian vegetation present throughout the southwestern United States are extremely important to wildlife, and especially so to avian communities. However, these narrow habitat bands would be greatly influenced by any changes (especially increased aridity) to present climatic regimes. Avian species numbers and community composition would be drastically altered, with the loss of many specialists that rely on riparian vegetation for nesting and food resources. Those parts of the southwestern avian community that would be most greatly impacted would be populations already at low levels (e.g., endangered species). This paper will present the potential impacts of global climate change (specifically reduced precipitation) throughout the southwest on three avian species, the Southwestern Willow Flycatcher (Empidonax traillii extimus), the Mexican Spotted Owl (Strix occidentalis caurina), and the Bald Eagle (Haliaeetus leucocephalus).


willow flycatcher The one species that would be most greatly impacted would be the endangered Southwestern Willow Flycatcher. There are four generally recognized subspecies of the Willow Flycatcher (Empidonax traillii), each of which has a distinct breeding range (see range map below):

Some recent research suggests there may be a fifth subspecies (E.t. campestris) distinct from E.t. traillii and occupying breeding areas in the northern and western portions of E.t. traillii range.

The breeding range distribution of the races of the Willow Flycatcher. Modified from Unitt (1987) and Browning (1993).

The Southwestern Willow Flycatcher breeds in dense riparian habitats along rivers, streams, or other wetlands. The vegetation can be dominated by dense growths of willows (Salix sp.), seepwillow (Baccharis sp.), or other shrubs and medium-sized trees. There may be an overstory of cottonwood (Populus sp.), tamarisk (Tamarix sp.), or other large trees, but this is not always the case. In some areas, the flycatcher will nest in habitats dominated by tamarisk and Russian olive (Eleagnus angustifolia). One of the most important characteristics of the habitat appears to be the presence of dense vegetation, usually throughout all vegetation layers present.

Almost all Southwestern Willow Flycatcher breeding habitats are within close proximity (less than 20 yards) of water or very saturated soil. This water may be in the form of large rivers, smaller streams, springs, or marshes. At some sites, surface water is present early in the nesting season, but gradually dries up as the season progresses. Ultimately, the breeding site must have a water table high enough to support riparian vegetation.

Photographs of a few known Southwestern Willow Flycatcher breeding areas are shown below. These examples are presented to show the wide diversity of sites where flycatchers have been found to breed.

Alpine, AZ, near the San Franciso River. Elevation approximately 8000 feet. Habitat is composed of a matrix of dense Geyer's Willow, approximately 3-4 m high. Soil is saturated most of the breeding season, but no open water nearby.

Roosevelt Lake, AZ, near the Salt River inflow. Elevation approximately 4000 feet. Habitat is composed of an extremely dense tamarisk monoculture, approximately 25-30 feet high. The vegetation is rooted in standing water some years, but in other years the soil has dried by the late breeding season.

Verde River, AZ, along the Verde River. Elevation approximately 4500 feet. Habitat is composed of a dense multi-storied mixture of tamarisk and native vegetation, ranging from 20-40 feet high. The overstory is dominated by tall cottonwoods. The patch is adjacent to the Verde River, and has a small spring-fed stream running throughout.

San Marcial, NM, along the Rio Grande. Elevation approximately 3000 feet. Habitat is composed of a dense multi-storied mixture of tamarisk and native vegetation, ranging from 20-30 feet high. The patch is adjacent to the Rio Grande, and may be flooded during high water years but dry later in the season.

Some Commonly Asked Questions About the Southwestern Willow Flycatcher:

Why was the Southwestern Willow Flycatcher listed as endangered?

The Southwestern Willow Flycatcher has declined during the last 100 years, primarily due to the loss, fragmentation, and modification of riparian habitats. In 1993, the U.S. Fish and Wildlife Service formally proposed to list the flycatcher as a federal endangered species, and to designate critical habitat (Federal Register 58:pages 39495-39522, July 23, 1993). In a 1995 ruling, the Service found that the flycatcher population was currently very low and faced a significant threat of extinction unless protected. Therefore, the flycatcher was listed as endangered, but designation of critical habitat was postponed (Federal Register 60:10694-10715, February 27, 1995).

How many Southwestern Willow Flycatchers remain?

Based on recent surveys coordinated by various state and federal agencies, fewer than 500 breeding pairs of the Southwestern Willow Flycatcher remain throughout its range. Surveys have also shown that the breeding sites are widely scattered and isolated, and most sites include fewer than five breeding pairs.

How does the Southwestern Willow Flycatcher differ from the other races of the Willow Flycatcher?

There are four or five recognized subspecies (races) of the Willow Flycatcher (Empidonax traillii). These subspecies are distinguished primarily by subtle differences in color and morphology (size and shape). The Southwestern Willow Flycatcher is somewhat paler, and has slightly different wing and tail length ratios. Each of the four subspecies occupy distinct breeding ranges.

Is the Southwestern Willow Flycatcher doomed to extinction?

The flycatcher population has clearly declined, and is currently very small and fragmented. However, with effective protection of the flycatcher and its remaining breeding habitat, combined with restoration and enhancement of southwestern riparian systems, the Southwestern Willow Flycatcher may recover and continue as a valuable component of our riparian ecosystems.

What can I do to help?

Lend your support to the protection and enhancement of riparian habitats, particularly in the arid southwest. If you know of a site where Southwestern Willow Flycatchers are breeding, contact your state or federal wildlife agency contacts.

Let your local, State, and Federal officials know your position regarding conservation of the Willow Flycatcher and other neotropical migrants and their riparian habitats.

Keep informed through local and regional conservation groups about activities that may affect neotropical migratory birds and their habitats.

Increase our understanding of the status and distribution of all neotropical migratory birds in Arizona by participating in the Arizona Breeding Bird Atlas Project.

Research and Data Needs for the Endangered Southwestern Willow Flycatcher (Empidonax traillii extimus)

The Arizona Partners in Flight (APIF) Master Plan (Sferra et al. 1994) outlines a set of goals and objectives for inventory and monitoring, research, information and education, management, and international issues involving neotropical migratory bird species. A major focus of APIF has been a three-year survey and monitoring effort for the southwestern willow flycatcher, listed as endangered by the U.S. Fish and Wildlife Service on March 29, 1995. This effort has greatly enhanced our knowledge of the status and distribution of the flycatcher in Arizona. An additional result of this effort has been the formulation and refinement of research and data needs that bear directly on the management and overall recovery of this species.

One of the goals of the APIF Master Plan is to "identify and set priorities for research needs and facilitate research for neotropical migratory birds and their habitats in Arizona" (Sferra et al. 1994). In partial fulfillment of this goal the following list has been developed for the southwestern willow flycatcher. This list was compiled from conversations with agency resource managers and biologists, agency and private researchers currently working on the flycatcher, and from recommendations in reports or published literature on the flycatcher. This draft list is constantly evolving as new data or management actions raise new questions. Priority or rankings have not been assigned. Future additions are likely, all comments are welcome.


1. Need: Recent surveys have been conducted in many riparian areas region-wide and have increased our knowledge of the southwestern willow flycatcher's distribution and status. However, many areas of suitable or potential habitat remain unsurveyed. Given the low population and patchy distribution of this species, it is important to intensify efforts to find and verify all breeding sites.
Task: Expand ground survey efforts to determine status/distribution in: CA - Santa Margarita River and tributaries, Santa Ynez River, Otai River, Sweetwater River; AZ - lower Colorado River, Bill Williams River, Gila River, Little Colorado River and tributaries; NM - Rio Grande; TX - Rio Grande, Pecos; CO -Dolores River; UT - Virgin River, Green River, San Juan River, Santa Clara River, Escalante River.
Scale: Local, site-specific to regional.
Target Initiation Date: 1996.
Duration of Study: 3 - 4 years.

2. Need: Southwestern willow flycatcher breeding sites are widely scattered across the regional landscape. Given the large amount of area surveyed, as well as the large number of people and agencies conducting surveys, it is critical that a system be developed to record and track known flycatcher breeding sites, unoccupied areas that have been surveyed, and areas that should be surveyed. Such a system will enable managers and researchers to (1) understand the ecosystem and landscape aspects of flycatcher distribution and habitat use, (2) effectively monitor what sites have been surveyed (to avoid duplication of effort), (3) determine where future efforts should be directed, and (4) develop a management tool for evaluating and implementing habitat conservation.
Task: Database/GIS of survey data and potential habitat (e.g., all sites surveyed; historic locations, extant locations, breeding status).
Scale: Rangewide (consolidate data from all states).
Target Initiation Date: 1996.
Duration of Study: One year initial focused effort with annual or biennial updates as population distribution changes.


3. Need: We are only beginning to understand how habitat patch size, shape, and proximity to water and other resources affects the suitability of habitat and the way in which flycatchers will use a site. Habitat patch characteristics of this scale can only be determined using high resolution aerial photographs. Aerial photographs are invaluable for mapping the distribution of territories at a breeding site and for aiding in estimating population size.
Task: Obtain low-level aerial photos of habitat for extant breeding locations.
Scale: All breeding locations rangewide.
Target Initiation Date: 1996.
Duration of Study: In conjunction with ongoing survey/monitoring efforts.

4. Need: Research, inventory, and conservation efforts undertaken for the southwestern willow flycatcher must be based on a quantitative understanding of flycatcher habitat. Currently, flycatcher habitat is measured and quantified differently by various researchers and agencies, making detection of general patterns and comparisons among sites difficult.
Task: Develop and implement quantitative habitat descriptions of riparian patches, territories, and nest sites occupied by flycatchers (e.g., vegetation characteristics, topographical setting, hydrological characteristics, environmental characteristics of nest sites).
Scale: Local, site-specific, regional, and rangewide incorporating mixed riparian, monotypic native, and monotypic exotic habitats.
Target Initiation Date: 1996.
Duration of Study: In conjunction with ongoing survey/monitoring for a minimum of five years.


5. Need: Of the approximately 40 currently known breeding sites rangewide, we have detailed data on breeding biology and population dynamics from only one site (Kern River in CA). Critical to the development of a conservation strategy or recovery plan is an understanding of flycatcher movement among breeding sites. Data on immigration/emigration rates and dispersal patterns are critical for understanding this species' dynamics across the entire range.
Task: Determine patterns of philopatry/site fidelity, natal dispersal, and adult dispersal through banding studies and extensive regional presence/absence surveys.
Scale: All local studies integrated at a regional level.
Duration of Study: Minimum 3 to 5 years.

6. Need: Patterns of population demography (birth, death, productivity, survivorship, etc.) are the factors that govern flycatcher population size and trend. Knowledge of demography patterns in combination with dispersal and emigration/immigration data are critical for identifying populations that should receive priority for management.
Task: Population demography of adult and immature flycatchers including productivity of females and survivorship of adults and immatures.
Scale: Local monitoring at sites throughout range.
Target Initiation Date: 1996.
Duration of Study: Minimum 3 to 5 years.

7. Need: As a suboscine, willow flycatcher vocal behaviors are more likely influenced by genetics rather than learning, as is the case for oscine songbirds. The southwestern willow flycatcher appears to have a primary song that is distinguishable from other flycatcher subspecies. If confirmed, song could be used to distinguish birds in the field eliminating the need to capture birds for positive identification. In addition, subspecific song patterns may yield important data relative to the distribution of and degree of differentiation between flycatcher subspecies.
Task: Expand current flycatcher vocalization study to determine local/population and/or sub-specific differences in primary song throughout range.
Scale: Throughout range of Empidonax traillii extimus, E.t. brewsteri, E.t. adastus, E.t. campestris.
Target Initiation Date: 1996.
Duration of Study: 2 years.

8. Need: Southwestern willow flycatcher breeding populations are extremely small and widely-separated. Some breeding populations may be isolated. Species with these characteristics often have low genetic diversity, with potential for low productivity and survivorship. Management and recovery of the flycatcher should be guided, in part, by an understanding of current population genetics at local and regional scales in order to preserve maximum genetic diversity.
Task: Determine current genetic variability for E.t. extimus rangewide.
Scale: Rangewide sampling including small and large populations, isolated (e.g. Big Sandy, Grand Canyon) and non-isolated populations (e.g., San Pedro River, Kern river, Rio Grande in NM).
Target Initiation Date: 1996.
Duration of Study: 2 years.

9. Need: The southwestern willow flycatcher was formerly more common and widespread, and breeding populations were less isolated. Consequently, it is assumed that genetic diversity was higher at both local and regional scales. A large number of museum specimens were collected at the turn of the century across the species' range, and provide material for determining historic levels and patterns of genetic diversity. These can be compared with current patterns (see # 8 above) and used to evaluate genetic and conservation consequences of population fragmentation and decline.
Task: Determine historic genetic variability from museum specimens used in Unitt's (1987) status and distribution paper.
Scale: Range-wide contingent upon availability of museum specimens.
Target Initiation Date: 1997.
Duration of Study: 2 years.

10. Need: There are currently four or five recognized subspecies of the willow flycatcher in North America. Taxonomic evaluations have been based on subtle differences in plumage coloration and body measurements. These characteristics are more difficult to distinguish in areas where putative subspecies intergrade, such as in central Utah and southwestern Colorado where E.t. adastus may occur. Although genetic studies have been undertaken to support separation of the willow and alder flycatchers, genetic studies on the validity of currently accepted flycatcher subspecies have not been conducted.
Task: Determine genetic basis for subspecies of willow flycatcher.
Scale: Rangewide for all putative subspecies.
Target Initiation Date: 1996.
Duration of Study: 2 years.


11. Need: The southwestern willow flycatcher is a neotropical migrant wintering in Mexico, Central America, and northern South America. Therefore, it spends less than half of the year on its breeding grounds in the American Southwest. Conservation and management of the flycatcher requires knowledge of historic patterns of distribution to provide baseline information for an evaluation of current status, habitat use, and threats on its migration and wintering grounds (see # 12 below).
Task: By locating historic specimens and records of willow flycatchers in the non-breeding season, determine historic distribution of southwestern willow flycatchers during the non-breeding season. This can also help identify areas that should be surveyed for current wintering habitat.
Scale: Regional to rangewide dependent on availability of specimens.
Target Initiation Date: 1996.
Time Frame: Comparison of museum specimens 6 months - 1 year.

12. Need: Conservation and management of this neotropical migratory species should include an understanding of its non-breeding season habitat use and ecology, as reflected in current patterns of distribution. In addition, we need to determine critical winter and migration habitats so that an assessment of their conservation needs can be made.
Task: By conducting intensive, standardized flycatcher surveys on potential wintering grounds, determine current distribution of southwestern willow flycatchers during non-breeding season.
Scale: Begin by surveying historic locations rangewide as determined by above museum work and expand to include other potential wintering areas as funding and effort allow.
Target Initiation Date: 1997.
Duration of Study: 3 - 4 years.


13. Need: Food resources are a vital component of willow flycatcher habitat, both for maintenance of breeding individuals and for provisioning of young. The willow flycatcher is an aerial insectivore. Its use of habitat may be strongly influenced by availability of prey. Invertebrate composition is influenced by the vegetation and hydrologic characteristics of local habitat. Currently, we know very little about the composition of willow flycatcher prey nor patterns of prey availability.
Task: Determine prey selection by flycatchers and prey abundance including seasonal patterns.
Scale: Multiple sites within region or throughout range.
Target Initiation Date: 1997.
Duration of Study: At least 1 to 2 years per site.


14. Need: Management of southwestern willow flycatcher populations requires and understanding of real and potential threats, particularly to flycatcher productivity. If productivity falls below a certain threshold, the population will not be maintained over time. In many areas, nest failure is one of the major factors influencing productivity of breeding songbirds. Causes and patterns of nest failure vary spatially and temporally, and long-term patterns may be important. Data on predation is needed from a larger sample of breeding populations in order to assess its effects on productivity rangewide.
Task: Determine causes of nest failure to evaluate spatial and temporal patterns of predation and their effects on productivity.
Scale: All data collected locally and aggregated at regional scales.
Target Initiation Date: on-going.
Duration of Study: 2 to 5 years.

15. Need: A significant number of flycatcher breeding sites are near roads, bridges, recreation areas, or areas of anticipated road maintenance or construction. Several studies suggest that roads and other disturbances may have a negative affect on locally breeding birds, both through direct collision impact and by reducing local breeding productivity. Given the small size and number of flycatcher breeding populations, it is important to understand how a breeding area may be affected by human activities noted above.
Task: Determine effects of ambient noise levels resulting from potential sources of disturbances (e.g. traffic, construction) on breeding behavior of flycatchers.
Scale: Project specific locations plus control sites.
Target Initiation Date: 1996.
Duration of Study: Agency action-driven, at least one year per site.

16. Need: Willow flycatcher populations experiencing brood parasitism by the brown-headed cowbird have declined or, at a minimum, have had reduced productivity. Cowbird control programs have stabilized flycatcher populations in some areas, and may be an effective tool for minimizing cowbird impacts. Cowbird control can be effective if implemented at cowbird concentration sites, if these sites can be determined. An understanding of daily and seasonal cowbird movement patterns is important in effectively evaluating and managing the cowbird threat. We currently know little of cowbird population size and movement patterns at the vast majority of flycatcher breeding sites.
Task: Utilize banding and radio-telemetry studies to determine local cowbird population characteristics and movement patters.
Scale: Local, emphasizing areas with known cowbird parasitism.
Target Initiation Date: 1996.
Duration of Study: At least one year per site.


mexican spotted owl The Mexican spotted owl occurs in forests and rocky canyonlands throughout the southwestern United States and Mexico. The breeding range extends from the southern Rocky Mountains in Colorado and the Colorado Plateau in southern Utah, south through Arizona and New Mexico, and extends along the Sierra Madre Occidental mountains to the southern end of the Mexican Plateau. A recent genetic study found one major allelic difference between the two coastal subspecies (S. o. caurina, and S. o. occidentalis) and the Mexican subspecies of spotted owls. Thus, lucida, perhaps separated from the coastal forms for many hundreds of years, may be a separate species.

Although widely distributed in the southwest, this bird is restricted to isolated tracts of breeding habitat and may be susceptible to habitat loss and climate change due to the owl¹s dependence on certain microhabitats that mimic mature forests. Dramatic climate change could profoundly alter the distribution and breeding density of spotted owls in the southwest United States through alterations in the extent of suitable habitat. In response to perceived threats by timber harvest, habitat loss due to fire, increased predation due to habitat fragmentation, and lack of adequate protective regulations, the Mexican spotted owl was listed as a threatened species in 1993.

Many aspects of the ecology of Mexican spotted owls have been documented in the southwest, particularly Arizona and New Mexico. In this region the owl is found associated with mixed conifer forest and uses mature stands more frequently than managed stands. In Utah, the owl primarily is associated with steep sandstone canyons with small patches of woodland habitat. Two studies in Utah described prey species found in regurgitated pellets and identified bushy-tailed woodrats (Neotoma cinerea), desert woodrats (Neotoma lepida) as the primary prey. The strong dependence on wood rats and the association with rocky canyonlands, suggests that spotted owls nest and forage primarily within non-forested areas in the state.

The Mexican Spotted Owl relies on cool and shady habitats in the southwest. The birds forage primarily on small rodents. Any climatic disturbance that would alter the distribution and phenology of plants within the forests, could alter the landscape in a negative way for both spotted owls and their small mammal prey. Changes in plant distribution and density could eliminate important nest and roost sites and cause extirpation of the small mammal prey. In addition, it is thought that spotted owls are heat intolerant and occupy dense forest in order to avoid high temperatures. Increases in ambient temperatures during the nest season could lead to nest failure and territorial abandonment. Ecologically, the owl appears to exhibit patterns of distribution strongly tied to dense and cool conifer forests. The majority of spotted owl nest sites that have been found in the southwest are located in mature forests. Owls that occupy the driest (or xeric) portions of their range will be threatened first, which could result in higher population fragmentation and genetic isolation. Given the threatened status of the owl, monitoring effects of climate change are highly warranted. It is critical that we continue to monitor habitat associations and vegetation, as well as spotted owl distributional patterns in the southwestern U. S., as climatologists document global warming patterns.


bald eagle A third avian species that would be greatly impacted by reduced precipitation throughout the southwest would be our national bird, the Bald Eagle. This bird congregates along riparian habitat through the southwest in winter to feed on fish or to hunt in ice-free water (van Riper et al. 1995). It is widely recognized that the construction and operation of reservoirs has also had a dramatic influence on wintering and migrant Bald Eagles (Southern 1963; Spencer 1976; Stalmaster 1987; Steenhof 1978). In contrast to reservoir-induced destruction of riverine habitat upon which many wintering Bald Eagles have traditionally relied, reservoirs may harbor, in some instances, new or alternative food sources (Jenkins 1992; Spencer 1976). However, any reduction in total precipitation would reduce stream habitat and water surface area available to foraging eagles.

Aerial censuses found that wintering Bald Eagles were present each year along the Colorado River corridor from late fall (October -November) through early spring (March-April) (van Riper et al. 1995). Bald Eagles were generally distributed evenly along the river corridor except in January-February when conditions were suitable and rainbow trout were spawning (Leibfried and Montgomery 1993). During these 2 months birds concentrated at the small tributaries, such as Nankaweap Creek. The trend of Bald Eagle numbers at Nankaweap Creek closely followed numbers of spawning trout that were recorded in the creek. During 1990-91 van Riper and Sogge (1996) recorded the highest known Bald Eagle concentration in the southwest at Nankaweap Creek, with up to 26 eagles present on a peak day. Approximately 70 to 100 individual eagles were documented during the eagle concentration (that time when at least 10 eagles were present each day) from 8 February to 8 March 1990. The previous high of 18 wintering eagles was present at Nankoweap in February 1988 (Brown et al. 1989).

Bald Eagle numbers are greatly influenced by spawning fish, which are in turn greatly influenced by stream water levels. In those years of lower precipitation spawning does not occur (Leibfried and Montgomery 1993). With the onset of global warming, the precipitation pattern is predicted toward reduced levels in the southwest, which would mean fewer numbers of trout and birds. For example, in 1993 when spawning was extremely low in Nankaweap Creek, there were concomitantly low numbers of eagles. This bird does, however, have the ability to make long seasonal movements in search of food. During 1992-1994, with low wintering Bald Eagle numbers along the Colorado River, there were reported concentrations of Bald Eagles at other locations on the southern Colorado Plateau. During 1993 Arizona Game and Fish (pers comm) reported up to 20 eagles at Lake Mary, just east of Flagstaff, Arizona. These birds were feeding on the thousands of rainbow trout that the agency had stocked into the lake during the winter. In 1994, another year of low Bald Eagle numbers along the Colorado River corridor, there were numerous reports from state and federal agency biologists of small eagle concentrations at elk and deer carcasses over the southern Colorado Plateau.

The status of Bald Eagles (Haliaeetus leucocephalus) in the southwestern U.S., especially along portions of the Colorado River, could be greatly influenced by climatic changes. This is especially true as impacts of reduced precipitation negatively influence numbers fish in streams and lakes. For example, at Nankaweap Creek the trend went upward from a few birds starting in the mid 1980s, to peak numbers in 1990-1991. In following years (1992-1994), lower precipation patterns resulted in poor rainbow trout spawning and lower numbers of bald eagles frequenting this location. Creek morphology and flow conditions varied among years and influenced the availability of trout, and thus eagle numbers. However, the Bald Eagle concentration at Nankoweap can be the largest such concentration in the southwestern United States. The 70 to 100 individual eagles recorded during the 1990 concentration represent what is believed to be one-fourth of the entire population of Bald Eagles wintering to the south of the Grand Canyon (in Arizona and northern Mexico). Concentrations of Bald Eagles noted in other areas of the southern Colorado Plateau, when lower numbers were recorded along the Colorado River, suggest widespread eagle movements over the region. Bald Eagles appear to be concentrating in areas that have the most abundant and available food resources, and these locations would be reduced as precipitation declined from global warming.


Willow Flycatcher

There are many references and reports related to the willow flycatcher; so many in fact, that it would be difficult to read through them all. However, the following references provide excellent summaries that will familiarize the reader with the regional status and biology of the Southwestern Willow Flycatcher.

Hubbard, J.P. 1987. The status of the willow flycatcher in New Mexico. Endangered Species Program, New Mexico Department of Game and Fish, Santa Fe, NM. 29 pp.

Maynard, W.R. 1994. Summary of 1994 Survey Efforts in New Mexico for the Southwestern Willow Flycatcher (Empidonax traillii extimus). New Mexico Department of Game and Fish (contract # 94-516-69), Santa Fe.

Sferra, S.J., R.A. Meyer, and T.E. Corman. 1995. Arizona Partners in Flight 1994 Southwestern Willow Flycatcher Survey. Final Technical Report 69, Nongame and Endangered Wildlife Program, Arizona Game and Fish Department.

Sogge, M.K., R.M. Marshall, S.J. Sferra and T.J. Tibbitts. 1997. A southwestern willow flycatcher natural history summary and survey protocol. National Park Service Technical Report NPS/NAUCPRS/NRTR-97/12.

Unitt, P. 1987. Empidonax traillii extimus: An endangered subspecies. Western Birds 18:147-162.

U.S. Fish and Wildlife Service. 1993. Proposal to list the Southwestern Willow Flycatcher as an endangered species and to designate critical habitat. July 23, 1993, Federal Register 58:39495-39522.

Whitfield, M.J. 1990. Willow Flycatcher reproductive response to brown-headed cowbird parasitism. Master's Thesis, California State University, Chico, California. 25 pp.

Whitfield, M.J. and C.M. Strong. 1995. A Brown-headed Cowbird control program and monitoring for the Southwestern Willow Flycatcher, South Fork Kern River, California. California Department of Fish and Game, Bird and Mammal Conservation Program Report 95-4, Sacramento. 17 pp.

Spotted Owl

Atwood, N.D., C.L. Pritchett, R.D. Porter, and B.W. Wood. 1980. Terrestrial vertebrates of the Kaiparowits Basin. Great Basin Nat. 40:303-350.

Baars, D.L. 1986. The Colorado Plateau: A Geologic History. Univ. Of New Mexico Press, Albuquerque. 279pp.

Barnsley, M.F. 1993. Fractals Everywhere. Academic Press Professional. Boston. 531pp.

Barrowcloug, G.F., and R.J. Gutierrez. 1990. Genetic variation and differentiation in the spotted owl. Auk 107:737-744.

Barrows, C.W. 1981. Roost selection by spotted owls: An adaptation to heat stress. Condor 83:302-309.

Barrows, C.W., and K. Barrows. 1978. Roost characteritics and behavioral thermoregulation in the spotted owl. Western birds 9:1-8.

Brown, D. E. 1982. Biotic communities of the American southwest-United States and Mexico. Desert Plants 1-4. 342pp.

Call, D.R. 1990. Home-range and habitat use by spotted owls in the central Sierra Nevada. M.S. Thesis, Humboldt State University, Arcata, CA.

Carey, A. B., J. A. Reid, and S. P. Horton. 1990. Spotted owl home range and habitat use in southern coast ranges. J. Wildl. Manage. 54:11-17.

Cully, J., and W. Austin. 1993. Endangered and threatened wildlife and plants; listing of the Mexican Spotted Owl as threatened. Fed. Reg. 58:14248-14271.

Forsman, E. D. 1983. Methods and materials for locating and studying spotted owls. Gen. Tech. Rep. PNW-162. Portland Oregon; U.S. Dept. of Agri., Fors. Serv., Pacific Northwest Forest and Range Exp. Sta. 8p.

Forsman, E.D., E. C. Meslow and H. M. Wight. 1984. Distribution and biology of the spotted owl in Oregon. Wildl. Monogr. 87. 64pp.

Franklin, A. B., J. P. Ward, R. J. Gutierrez, and G. I. Gould, Jr. 1990. Density of northern spotted owls in northwest California. J. Wildl. Manage. 54:1-10.

Ganey, J. L. 1990. Calling Behavior of spotted owls in northern Arizona. Condor 92:485-490. Ganey, J. L., and R. P. Balda. 1989a. Distribution and habitat use of Mexican spotted owls in Arizona. Condor 91:355-361.

Ganey, J. L., and R. P. Balda. 1989b. Home range characteristics of spotted owls in northern Arizona. J. Wildl. Manage. 53:1159-1165.

Ganey, J.L., and R.P. Balda. 1994. Habitat Selection by Mexican Spotted Owls in northern Arizona. Auk 111:162-169.

Ganey, J.L., R.P. Balda, and R.M. King. 1993. Metabolic rate and evaporative water loss of Mexican spotted owls and great horned owls. Wilson Bull. 105:645-656.

Gould, G. I. 1977. Distribution of the spotted owl in California. West. Birds 8:131-146.

Gutierrez, R.J. 1985. An overview of the recent research on the spotted owl, p. 39-49. In R.J. Gutierrez and A.B. Carey [eds.], Ecology and management of the spotted owl in the Pacific Northwest. Gen. Tech. Rep. PNW-185, USDA Forest Service, Portland, OR.

Howe, F., M.Britten, S. Hedges, S. Linner, S. Rinkevich, K. Grandison, and D. Willey. Suggestions for the management of Mexican spotted owls in Utah. Utah Div. Wildl. Res. Unpublished document, Salt Lake City.

Kertell, K. 1977. The spotted owl at Zion National Park, Utah. Western Birds 8:147-150.

Rinkevich, S. E. 1991. Distribution and habitat characteristics of Mexican spotted owls in Zion National Park, Utah. M.S. Thesis. Humboldt State Univ. 62pp.

Rinkevich, S.E., and R.J. Gutierrez. 1996. Mexican spotted owl habitat characteristics in Zion National Park. Raptor Res. 30:74-78.

Smith, R. N. 1990. Endangered and threatened wildlife and plants; finding on a petition to list the Mexican Spotted Owl as threatened or endangered. Fed. Reg. 55:90-7054.

Smith, R. N. 1991. Endangered and threatened wildlife and plants; proposal to list the Mexican Spotted Owl as threatened. Fed. Reg. 56:56344-56355.

Sovern, S. G., E. D. Forsman, B. L. Biswell, D. N. Rolph, and M. Taylor. 1994. Diurnal behavior of the spotted owl in Washington. Condor 96:200-202.

USDI 1995. Recovery Plan for the Mexican spotted owl.Albuquerque, New Mexico, 172pp.

Vaughan, T. 1986. Woodrats. pp. 180. In: CRC handbook of Census Methods for terrestrial vertebrates. CRC Press. Boca Raton, Florida. 397pp.

Verner, J., K. McKelvey, B.R. Noon, R.J. Gutierrez, G.I. Gould, and T.W. Beck. 1992. The California spotted owl: A technical assessment of its current status. USDA For. Ser. Gen. Tech. Rep. PSW-GTR-133.

Wagner, P.W., C.D. Marti, and T.C. Boner. 1982. Food of the spotted owl in Utah. Raptor Res. 16:27-28.

Willey, D. W. 1993. Home-range characteristics and juvenile dispersal ecology of Mexican Spotted Owls in southern Utah. Tech. Rep. submitted to the Utah Division of Wildlife Resources, Nongame Branch. Utah Division of Natural Resources Contract No. 91-2577, Amendment 2. 44pp.

Willey, D. W. 1994. Juvenile dispersal ecology of Mexican Spotted Owls in southern Utah. Annual Report 1994 submitted to the Utah Division of Wildlife Resources, Nongame Branch. Utah Division of Natural Resources Contract No. 91-2577, Amendment 2. 44pp.

Willey, D.W. 1995. Mexican Spotted Owls in Canyonlands of the Colorado Plateau.Pages 330-331 in E.T. LaRoe, G.S. Farris, C.E. Puckett, P.D. Doran, and M.J. Mac [eds.], Our Living Resources: a report to the nations on the distribution, abundance, and health of U.S. plants, animals, and ecosystems. U.S. Department of the Interior, National Biological Service, Washington, D.C.

Bald Eagle

Brown, B.T, S.W. Carothers, and R.R. Johnson. 1987. Grand Canyon birds; historical notes, natural history, and ecology. Tucson: University of Arizona Press, 302 pp.

Brown, B.T., R. Mesta, L.E. Stevens, and J. Weisheit. 1989. Changes in winter distribution of Bald Eagles along the Colorado River in Grand Canyon, Arizona. Journal of Raptor Research 23:110-113.

Jenkins, J. M. 1992. Ecology and behavior of a resident population of Bald Eagles. PhD Dissertation, University of California, Davis, CA.

Knight, R.L., and S.K. Knight. 1984. Responses of wintering Bald Eagles to boating activity. Journal of Wildlife Management 48:999-1004.

Leibfried, W.C. and W. L. Montgomery. 1993. Regulated flows, trout spawning, and abundance of Bald Eagles on the Colorado River, Grand Canyon National Park. In: Proceedings of the first biennial conference on research in Colorado Plateau national parks. editors, P.G. Rowlands, C. van Riper II and M. K. Sogge. Transactions and Proceedings Series NPS/NRNAU/NRTP-93/10, US Department of the Interior.

McClelland, B.R. 1973. Autumn concentrations of Bald Eagles in Glacier National Park. Condor 75:121-123.

McClelland, B.R., L.S. Young, D.S. Shea, P.T. McClelland, H.L.Allen, and E.B. Spettigue. 1982. The Bald Eagle concentration in Glacier National Park, Montana: Origin, growth, and variation in numbers. Living Bird 21:133-155.

Southern, W.E. 1963. Winter populations, behavior, and seasonal dispersal of Bald Eagles in northwestern Illinois. Wilson Bulletin 75:42-55.

Spencer, D.A., editor. 1976. Wintering of the migrant Bald Eagle in the lower 48 states. National Agricultural Chemicals Association, Washington, D.C. 170 pp.

Stalmaster, M.V. 1987. The Bald Eagle. Universe Books, New York. 227 pp.

Stalmaster, M.V., and J.R. Newman. 1978. Behavioral responses of wintering Bald Eagles to human activity. Journal of Wildlife Management 42:506-513.

Steenhof, K. 1978. Management of wintering Bald Eagles. USDI Fish and Wildlife Service Publication FWS/OBS-78/79, Washington, D.C. 59 pp.

van Riper, C., III, M. K. Sogge and T. J. Tibbitts. 1995. Wintering Bald Eagles Along the Colorado River Corridor. pp 328-330, In. Our Living Resources : a report to the nation on the distribution, abundance, and health of U.S. plants, animals, and ecosystems (Eds. E. T. LaRoe, G. S. Farris, C. E. Puckett, P. D. Doran, and M. J. Mac). Washington D.C. : U.S. Dept. of the Interior, National Biological Service, 530pp.


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