Effects of winter recreation on bald eagles

Authors(s): J. T. Stangl

Publication: Effects of winter recreation on wildlife of the Greater Yellowstone Area: a literature review and assessment. Report to the Greater Yellowstone Coordinating Committee. Yellowstone National Park, Wyoming.

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Publication Date: 0000-00-00

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Abstract: POPULATION STATUS AND TREND Nesting, wintering, and migrating populations of bald eagles (Haliaeetus leucocephalus) occur in the Greater Yellowstone Area (GYA). Bald eagles are protected under the Migratory Bird Treaty Act of 1918 (16 U.S. Code 703) and the Bald Eagle Protection Act of 1940 (16 U.S. Code 668). Bald eagles were initially listed as an endangered species under the Endangered Species Act of 1973 (U.S. Code 1531, 1982 amended), but on July 12, 1995, the bald eagle?s status was downlisted to threatened in the lower 48 states. This action did not alter those conservation measures already in place to protect the species and its habitats. Because of the eagle?s initial status as endangered, the Pacific States Bald Eagle Recovery Team was formed (the GYA is part of the Pacific Recovery Area). The team produced the Pacific Bald Eagle Recovery Plan (USFWS 1986), which addressed the recovery of bald eagles in Washington, Oregon, California, Nevada, Idaho, Montana, and Wyoming. Regionally, other teams were formed, and the Bald Eagle Management Plan for the Greater Yellowstone Ecosystem was issued in 1983 (revised 1996), and the Montana Bald Eagle Management Plan was issued in 1986 (revised 1994). Both plans identify threats to the bald eagle and provide management direction for population recovery in the respective areas. Three population units were delineated in the GYA based on bald eagle natural history and the elevation, climate, and vegetation of the units (GYBEWG 1996). The Snake Unit includes bald eagle breeding areas associated with the Snake River in northwestern Wyoming and southeastern Idaho. The Continental Unit includes the watersheds in southwestern Montana, the upper Henrys Fork, southeastern Idaho, and northwestern Wyoming. The Yellowstone Unit includes most of Yellowstone National Park. Between 1970 and 1995, the bald eagle population in the GYA increased exponentially. There were 111 known breeding areas in 1995 (GYBEWG 1996). Population growth has been attributed to the significant reduction of environmental contaminates, such as DDT (pesticide), and the initiation of intensive nesting surveys (Flath et al. 1991). LIFE HISTORY The average life span of a wild bald eagle is estimated to be between 10 and 18 years (MBEWG 1994). Bald eagles first breed at 6 to 7 years (Harmata and Oakleaf 1992) after adult plumage is acquired (Stalmaster 1987). Nest building most commonly occurs during the autumn, late winter, and early spring (October to April), although nest repair may occur during every season for well-established pairs. Alternate nests may be present in a breeding area. Incubation can begin as early as the first week of February and as late as the last week of March (Swensen et al. 1986, Harmata and Oakleaf 1992, Whitfield 1993, Stangl 1994) and lasts 35 days. Bald eagles are very sensitive to disturbance during nest building, egg laying, and incubation. Bald eagles are opportunistic feeders and prey on fishes, waterfowl, lagamorphs, some ground-dwelling mammals, as well as ungulate carrion. Bald eagles also steal prey from other eagles, osprey, otters, and many other species (Stalmaster 1987, Harmata and Oakleaf 1992, Stangl 1994). In the GYA, adult breeding pairs of eagles may or may not migrate out of the ecosystem during the winter (Harmata and Oakleaf 1992). Juvenile, immature, and adult eagles migrate at different times, therefore, age ratios of a population may differ during the winter. Juveniles migrate earlier in the autumn (Stalmaster 1987, Harmata and Oakleaf 1992) and may travel farther than sub-adults or adults (Stalmaster 1987). Band encounters and radio tracking of juvenile and immature bald eagles produced in the GYA indicated that virtually all birds leave the ecosystem in the first autumn after fledging. Juveniles return in mid-April to early May and appear to remain within the GYA during the summer. Juvenile eagles originating in Canada winter within the GYA. HABITAT WINTERING HABITAT Bald eagle winter habitat is generally associated with areas of open water (unfrozen portions of lakes and free-flowing rivers) where fishes and/or waterfowl congregate (Swensen et al. 1986, Stalmaster 1987, GYBEWG 1996). Most winter habitats include major rivers and large lakes. Eagles will forage on high-quality foods away from aquatic areas, in particular, upland areas where ungulate carrion, game birds, and lagomorphs are available (Swenson et al. 1986). Ungulate carrion associated with late-season hunter harvests and big game wintering areas are also important to wintering bald eagles (GYBEWG 1996). NESTING HABITAT Nesting habitat varies among units in the GYA. Nest sites are generally distributed around the periphery of lakes, reservoirs, and along rivers. Nests are most commonly constructed in mature or old-growth stands of large diameter trees that are multi-layered and contain a variety of species, primarily Douglas fir (Pseudotsuga menziesii), black cottonwood (Populus trichocarpa), and spruce (Picea spp.). Large emergent trees and snags provide important nesting and perching habitat (Wright and Escano 1986). Bald eagles display strong fidelity to a breeding area and often to a specific nest. An available prey base may be the most important factor determining nesting habitat suitability (Swensen et al. 1986, Harmata and Oakleaf 1992, MBEWG 1994), nesting density (Dzus and Gerrard 1993), and productivity (Hansen 1987) of bald eagles. Bald eagles usually nest as close to maximum foraging opportunities as possible, although human activity will be avoided (Harmata and Oakleaf 1992). ROOSTING HABITAT Like nesting and perching trees, roost trees are typically mature or old conifers or cottonwoods. Preferred roosting habitat includes a protected microclimate that provides shelter from harsh weather and is characterized by tall trees that extend above the forest canopy and by locations that provide clear views and open flight paths (Stalmaster 1987). Roost locations lie within the breeding territory during the breeding season. Bald eagles may roost in the nest or nest tree. As nestlings grow, the adults may roost farther away from the nest site (Stalmaster 1987). In many areas, night communal roosts are important during the fall and winter months. Although winter roosting habitat is not necessarily close to water or in close proximity to food sources, the availability of an abundant source of food, of foraging perches, and of secure night-roost sites away from human activities are important habitat components (GYBEWG 1996, MBEWG 1994). HUMAN ACTIVITIES Bald eagles may be affected by a variety of recreational, research, resource, and urban development activities. Pesticides, poisoning, electrocution, vehicle collisions, and shooting have directly affected eagles. Various types of human activities that influence the environment have indirectly affected eagles (Mathisen 1968, Knight and Knight 1984, Stalmaster 1987, Buehler et al. 1991, McGarigal et al. 1991, Harmata and Oakleaf 1992). Management concerns initially focused on permanent alterations of bald eagle habitat, such as cutting down nest trees. However, recent studies have demonstrated the importance of protecting eagle habitat from temporary human activities, such as recreation (Stalmaster and Newman 1978, Knight and Knight 1984, Knight et al. 1991, McGarigal et al. 1991, Harmata and Oakleaf 1992). Many recreational activities are focused on or around major water bodies where bald eagles nest, roost, or forage, thereby increasing the potential for eagle?human interactions. Temporary human activities have been shown to influence the behavior of wintering bald eagles (Stalmaster and Newman 1978, Knight and Knight 1984) and those in breeding areas (McGarigal et al. 1991, Harmata and Oakleaf 1992, Stangl 1994). Anthony et al. (1995) believe that the cumulative effects of recreational activities can have deleterious effects on eagle populations through reductions in survival, especially during the winter, and in reduced reproductive success (Montolopi and Anderson 1991). POTENTIAL EFFECTS Bald eagles are generally food-stressed during winter. High levels of human activity can potentially increase energy demands on wintering bald eagles and result in increased mortality rates (Stalmaster and Gessaman 1984). Juvenile bald eagles have higher energy demands, are less efficient foragers, and spend more time trying to acquire food than adults. Therefore, they are more likely to be adversely impacted by human activities. During the breeding season, bald eagles are most sensitive to human activities during nest building, egg-laying, and incubation (February 1 to May 30). Human activities during this time may cause nest abandonment. After young have hatched, a breeding pair is less likely to abandon the nest. However, eagles may leave the nest due to prolonged disturbances, exposing young to predation and adverse weather conditions (MBEWG 1994, GYBEWG 1996). Bald eagle responses to human activities generally range from displacement to avoidance of the human activity to reproductive failure. Bald eagle responses also vary depending on type, intensity, duration, timing, predictability, and location of the human activity. Responses may be influenced by the presence of another eagle nearby, the eagle?s physical and behavioral state, the nature of the human activity, and the time and location of the encounter (Anthony et al. 1995). Eagle responses to human activities may differ with populations (Fraser et al. 1985) and with individual pairs (Stangl 1994). Some bald eagles may habituate to human presence and become more tolerant of human activities (Knight and Knight 1984, Harmata and Oakleaf 1992, GYBEWG 1996). Human activities during the winter and spring can reduce feeding activities of bald eagles (Skagen 1980). These activities can also displace eagles from foraging areas (Stalmaster and Newman 1978), alter use patterns (i.e., eagles will avoid a feeding area for a period of time), or shift spatial- or temporal-use patterns (McGarigal et al. 1991, Harmata and Oakleaf 1992, Stangl 1994, Smith 1988). Vehicular activities along prescribed routes or within strict spatial limits and at relatively predictable frequencies are least disturbing to bald eagles (McGarigal et al. 1991, Stangl 1994, GYBEWG 1996). However, slow-moving motor vehicles can disrupt eagle activities more than fast-moving motor vehicles (McGarigal et al. 1991). Snowmobiles may be especially disturbing, probably due to associated random movement, loud noise, and operators who are generally exposed (Walter and Garret 1981). Bald eagles have been displaced by pedestrian activities (Stalmaster and Newman 1978, McGarigal et al. 1991, Stangl 1994) especially when the activities occur outside of predictable use areas (Harmata and Oakleaf 1992). Grubb and King (1991) found that pedestrians (hikers, anglers, and hunters) were the most disruptive type of human activities to bald eagles. Stangl (1994) found that a bald eagle pair used perches that were spatially separated from pedestrian angler activities. Bald eagles that forage on the ground are most sensitive to human activities (Stalmaster and Newman 1978, Knight and Knight 1984, McGarigal et al. 1991), therefore, human disturbances may have a greater impact on eagles foraging on fish or ungulate carcasses (Anthony et al. 1995). Riparian habitat is an important component of bald eagle habitat. Recreational impacts on riparian areas, specifically impacts to cottonwood trees, could affect bald eagle perch habitat as well as availability of prey. In the GYA, winter recreational activities that are most likely to affect wintering, migrating, and spring nesting bald eagles include: snowcoach and snowmobile traffic, cross-country skiing, telemark skiing, snowshoeing, dog sledding, late-season elk hunting, and antler collecting. (Bison management activities also have the potential to impact bald eagles.) Groomed trails are often located in riparian areas, and activities on these trails can begin as early as October and extend as late or later than June. A review of the literature revealed that research has not been completed to assess the effects of snowmobile or other winter recreational activities on bald eagle wintering or breeding habitat, but some documents referenced potential effects of snowmobile activities (Shea 1973, Alt 1980, Harmata and Oakleaf 1992, Stangl 1994). Bald eagles in the GYA are particularly affected by human use of the following Potential Opportunity Areas: (1) Destination areas (2) Primary transportation routes (3) Scenic driving routes (4) Groomed motorized routes (5) Motorized routes (6) Backcountry motorized areas (7) Groomed nonmotorized routes (8) Nonmotorized routes (9) Backcountry nonmotorized areas (10) Downhill sliding (nonmotorized) (12) Low-snow recreation areas MANAGEMENT GUIDELINES The Bald Eagle Management Plan for the Greater Yellowstone Ecosystem (GYBEWG 1996) established a management goal ?to maintain bald eagle populations in the GYA at high levels with high probabilities of persistence and in sufficient numbers to provide significance to the ecosystem, academic research, and readily accessible enjoyment by the recreational and residential public.? Management of bald eagle winter and spring habitat should focus on the presence and abundance of food for eagles that is usually associated with open water, the availability and distribution of foraging perches, the availability of secure night roost sites, and freedom from human harassment (Martell 1992). Adequate monitoring of bald eagle wintering and nesting populations is fundamental to effective management. Bald eagles may be ?urban? or ?rural? (GYBEWG 1996) and respond differently to recreation activities. Eagles in the vicinity of high human densities and recreational activities may become habituated to human presence and tolerant of certain human activities. Urban eagles may be exposed to human activities that increase gradually, usually within defined spatial limits, while human activities that rural eagles are exposed to are distributed and moving randomly at varying intensities and often seasonal and abrupt. In some winter recreation areas, eagles will initiate nest building while snowmobile activities are at their highest levels. The plan (GYBEWG 1996) suggested management guidelines with regard to winter recreation activities, including: 1. Encourage and support research to identify and quantify use and location of seasonal concentrations of bald eagles. 2. Establish buffer zones of 1,300 feet around high-use foraging areas with temporal restrictions from sunset to 10:00 a.m. in areas of high human use or establish site-specific modifications based on research findings. 3. Diurnal perching areas may not always be associated with primary foraging area. If separate, buffer zones of 650 to 1,300 feet around concentrated or high-use perches should be imposed, dependent on existing vegetative screening. Temporal restrictions should be consistent with seasonal residency. Removal of trees, especially snags greater than 2 feet in diameter that are within 100 horizontal feet or 1,300 feet in elevational rise of greater than 30 degrees from shoreline should be discouraged on private land and prohibited on federal land. Single trees in upland foraging areas devoid of elevated perch sites should be retained. 4. Areas of winter and early spring waterfowl concentrations are important to wintering and migrating eagles. Efforts to enhance existing wetlands and development of new ones should be supported. 5. Strive to maintain visual, temporal, and spatial integrity of the roost site in order to provide for short- and long-term use by bald eagles. Manage critical and vital roost sites temporally and spatially. Areas within 1,300 feet of critical and vital roosts should be closed. Human activity beyond 1,300feet may be disruptive if above the roost site. In such cases, methods to provide visual screening from the roost site should be explored and based on site inspection and recommendations of biologists. Closures for autumn roosts should extend from 1 October to 1 January, for winter roosts from 15 October to 1 April, for vernal roosts from 1 March to 15 April or determined by actual residency patterns of local eagles. Alternative schemes towards these ends should be encouraged to accommodate human values. 6. Strive for similar protection of secondary sites because they may evolve into critical or vital roosts through succession, fire, wind, or other catastrophe. Guidelines have been developed in the Bald Eagle Management Plan for the Greater Yellowstone Ecosystem (GYBEWG 1996) and the Montana Bald Eagle Management Plan (MBEWG 1994) to provide management direction for bald eagles where there is little information on areas actually used. The GYBEWG (1996, pages 22?25) defined three zones within bald eagle breeding areas to which these guidelines apply. Zone boundaries should be altered after intensive study of eagle activity and development of site specific management plans. Guidelines and recommendations for the completion of management plans focused on bald eagle habitat or breeding areas. ZONE I?NEST SITE AREA The area within a ?-mile radius of active nest sites should be maintained to protect nest site characteristics, including snags, nest trees, perch trees, roost trees, and vegetative screening. Any disturbances should be eliminated. 1. Human activity should not exceed minimal levels during the period from first occupancy of the nest site until two weeks following fledging (approximately 1 February to 15 August). Minimal human activity levels include essentially no human activity with the following exceptions: (1) existing patterns of ranching and agriculture, (2) nesting surveys and banding by biologist experienced with eagles, and (3) river traffic as defined by the GYBEWG (1996, page 22). Light human activity levels should not be exceeded during the rest of the year. Light human activity levels allow for day use and low impact activities such as boating, fishing, and hiking but at low densities and frequencies. Activities which are excluded include concentrated use associated with recreation centers (i.e., picnic areas, boat landings) and helicopters within 650 yards of the ground. 2. Habitat alterations should be restricted to projects specifically designed for maintaining or enhancing bald eagle habitat and conducted only during September through January. 3. Human activity restrictions for Zone I may be relaxed during years when a nest is not occupied. However, light human activity levels should not be exceeded and land-use patterns should not preclude a return to minimal activity levels. ZONE II?PRIMARY USE AREA This zone includes the area ?- to ?-mile from active nest sites in the breeding area where it is assumed that 75 percent of activities (foraging, loafing, bathing, etc.) of a bald eagle breeding pair occur. 1. Light human activity levels should not be exceeded during the nesting season. Moderate levels should not be exceeded during other times in the year. Moderate human activity include light impact activity levels but intensity of such activities are not limited. A limited number of recreation centers designed to avoid eagle conflicts may be considered. Other activities such as construction should be designed to specifically avoid disturbance. Designing projects or land uses to avoid eagle conflicts requires the sufficient data to formulate a site-specific management plan. 2. Habitat alterations should be carefully designed and regulated to ensure that preferred nesting and foraging habitat are not degraded. 3. Developments that may increase human activity levels and use patterns should not be allowed. ZONE III?HOME RANGE This area includes all suitable foraging habitat within 2.5 miles of active nest sites. Areas within the 2.5 mile radius of the nest that do not include potential foraging habitat may be excluded. However, the zone will include a 1,300 foot buffer along foraging habitat where the zone has been reduced. 1. Human activities should not exceed moderate. 2. Projects that could potentially alter the habitat of forage species should be carefully designed to insure availability of prey is not degraded. Adequate design of such projects will require data from site-specific management plans. 3. Terrestrial habitat alterations should ensure important components are maintained. Major habitat alterations should be considered only if site-specific management plans are developed and only if the alterations are compatible with management plans. 4. Permanent developments that are suitable for human occupancy should be avoided. Other developments that may increase human activity levels should be carefully designed to ensure that objectives would not be exceeded for all three management zones. For example, active nest sites or any nest sites in the breeding area that have been active in the last five years if the active nest has not been identified should be protected. Elk harvests occur during the fall and winter, and antler collecting occurs during the spring in various areas of the GYA. Gut piles and carcasses resulting from hunting activities provide a valuable foraging resource for wintering, migrating, and breeding bald eagles. Although some activities associated with the late hunt could displace bald eagles, hunting activities are generally completed early in the nesting season and the forage resulting from the harvest is probably more beneficial to bald eagles than the potential for displacement. This is not the case with antler collectors or ?horn hunters.? Horn hunting activities generally occur during the spring when bald eagles are nesting and are most sensitive to human disturbances. Dispersed activities associated with horn hunting could potentially impact nesting bald eagles if the activities occur around the nest site or in the primary foraging area. During winter and spring months, many wildlife species congregate at lower elevations. In the GYA, elk and moose are commonly observed along roadways and are periodically observed along designated and groomed snowmobile trails. Natural mortalities and road kill animals provide a winter and spring source of food for bald eagles. However, eagles can, in turn, become road kill victims themselves when foraging on carcasses located next to roads. Carcasses on and along roads should be moved away from the road edge in an effort to protect bald eagles and other scavengers. Similar incidents can occur along railroads where deer, elk, moose, and antelope may concentrate (J. Naderman, Idaho Department of Fish and Game, personal communication). Because a large portion of the GYA lies within the grizzly bear recovery area, road kill and some natural mortality carcasses are removed and are no longer available as a food source in an effort to reduce bear?human conflicts. LITERATURE CITED Alt, K. L. 1980. Ecology of breeding bald eagle and osprey in the Grand Teton? Yellowstone National Parks complex. Thesis, Montana State University, Bozeman, Montana, USA. Anthony, R. G., R. J. Steidl, and K. McGarigal. 1995. Recreation and bald eagles in the Pacific Northwest. Pages 223?241 in R. L. Knight and K. J. Gutzwiller, editors. Wildlife and recreation: coexistence through management and research. Island Press, Washington, D.C., USA. Buehler, D. A., T. J. Mersmann, J. D. Fraser, and J. K. D. Seegar. 1991. Effects of human activity on bald eagle distribution on northern Chesapeake Bay. Journal of Wildlife Management 55:282?290. Dzus, E. H., and J. M. Gerrard. 1993. Factors influencing bald eagle densities in northcentral Saskatchewan. Journal of Wildlife Management 57:771?778. Flath, D. L., R. M. Hazlewood, and A. R. Harmata. 1991. Status of the bald eagle (Haliaeetus leucocephalus) in Montana: 1990. Proceedings Montana Academy of Science 51:15?32. Fraser, J. D., L. D. Frenzel, and J. E. Mathisen. 1985. The impact of human activities on breeding bald eagles in northcentral Minnesota. Journal of Wildlife Management 49:585?592. Greater Yellowstone Bald Eagle Working Team. 1983. A bald eagle management plan for the Greater Yellowstone Ecosystem. Wyoming Game and Fish Department, Cheyenne, Wyoming, USA. GYBEWG (Greater Yellowstone Bald Eagle Working Group). 1996. Greater Yellowstone bald eagle management plan: 1995 update. Wyoming Game and Fish Department, Lander, Wyoming, USA. Grubb, T. C., and R. M. King. 1991. Assessing human disturbance of breeding bald eagles with classification tree models. Journal of Wildlife Management 55:500?511. Hansen, A. J. 1987. Regulation of bald eagle reproductive rates in southeast Alaska. Ecology 68:1387?1392. Harmata, A. R., and R. Oakleaf. 1992. Bald eagles in the Greater Yellowstone Ecosystem: an ecological study with emphasis on the Snake River, Wyoming. Wyoming Game and Fish Department, Cheyenne, Wyoming, USA. Knight, R. L., and S. K. Knight. 1984. Responses of wintering bald eagles to boating activity. Journal of Wildlife Management 48:999?1004. Knight, R. L., D. P. Anderson, and N. V. Marr. 1991. Responses of an avian scavenging guild to anglers. Biological Conservation 56:195?205. Martell, M. 1992. Bald eagle winter management guidelines. U.S. Fish and Wildlife Service, Region 3, Minneapolis, Minnesota, USA. Mathisen, J. E. 1968. Effects of human disturbance on nesting bald eagles. Journal of Wildlife Management 32:1?6. McGarigal, K., R. G. Anthony, and F. B. Isaacs. 1991. Interactions of humans and bald eagles on the Columbia River Estuary. Wildlife Monograph Number 115. MBEWG (Montana Bald Eagle Working Group). 1986. Montana bald eagle management plan. U.S. Bureau of Reclamation, Billings, Montana, USA. ???. 1994. Montana bald eagle management plan. U.S. Bureau of Reclamation, Billings, Montana, USA. Montopoli, G. J., and D. A. Anderson. 1991. A logistic model for the cumulative effects of human intervention on bald eagle habitat. Journal of Wildlife Management 55:290?293. Shea, D. S. 1973. A management-oriented study of bald eagle concentrations in Glacier National Park. Thesis, University of Montana, Missoula, Montana, USA. Skagen, S. K. 1980. Behavioral response of wintering bald eagles to human activity on the Skagit River, Washington. Pages 231?241 in R. L. Knight, G. T. Allen, M. V. Stalmaster, and C. W. Servheen, editors. Proceedings of the Washington Bald Eagle Symposium. The Nature Conservancy, Seattle, Washington, USA. Smith, T. J. 1988. The effect of human activities on the distribution and abundance of the Jordan Lake?Falls Lake bald eagles. Thesis, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA. Stalmaster, M. V. 1987. The bald eagle. Universe Books, New York, New York, USA. ???, and J. R. Newman. 1978. Behavioral responses of wintering bald eagles to human activity. Journal of Wildlife Management 42:506?513. Stalmaster, M. V., and J. A. Gessaman. 1984. Ecology energetics and foraging behavior of overwintering bald eagles. Ecological Monograph 54:407?428. Stangl, J. M. 1994. Effects of monitoring effort and recreation patterns on temporal and spatial activities of breeding bald eagles. Thesis, Montana State University, Bozeman, Montana, USA. Swenson, J. E., K. L. Alt, and R. L. Eng. 1986. The ecology of the bald eagle in the Greater Yellowstone Ecosystem. Wildlife Monograph Number 95. USFWS (U.S. Fish and Wildlife Service). 1986. Recovery plan for the Pacific bald eagle. Portland, Oregon, USA. Walter, H., and K. L. Garrett. 1981. The effects of human activity of wintering bald eagles in the Big Bear Valley, California. Final report to the U.S. Forest Service, Big Bear District, Fawnskin, California, USA. Whitfield, M. B. 1993. South Fork Snake River bald eagles research project. Final report to the Bureau of Land Management, Idaho Falls District, Idaho Falls, Idaho, USA. Wright, M., and R. E. Escano. 1986. Montana bald eagle nesting habitat macro-habitat description. U.S. Forest Service, Missoula, Montana, USA. PREPARED BY: J. T. Stangl, Wildlife Biologist, U.S. Forest Service, Gallatin National Forest, West Yellowstone, Montana, USA.

Keywords: bibliography, Animal, Bird, Aves, Ornithology, Eagle, Bald eagle, Haliaeetus leucocephalus, Raptor, Snake River, Teton County, Jackson Hole, Greater Yellowstone Ecosystem, Human activity, Wildlife, Management, Habitat, Idaho, Yellowstone National Park, Population, Mortality, Nest, Nesting, Breeding, Predation, Lagomorph, Mammal, Ungulate, Osprey, Otter, Fish, Migration, Radio collar, Food, Forage, Hunting, Wildlife, Elk, Cervidae, Cervus elaphus, Wapiti, Moose, Alces alces