Bald Eagle - Haliaeetus leucocephalus
State Rank Reason (see State Rank above)
Populations numbers have steadily increased since the 1980s and breeding pairs now occupy a high percentage of suitable habitat across the state. However the species is still protected under the Bald and Golden Eagle Protection Act of 1940.
- Details on Status Ranking and Review
ScoreD - 1,000-2,500 individuals
CommentThe FWP Bald Eagle database documented 550 breeding territories in 2010 which indicates a minimum breeding population size of 1,100 individuals which seems to solidly place them in the 1,000 to 2,500 category.
ScoreG - 200,000-2,500,000 km squared (about 80,000-1,000,000 square miles)
Comment380,531 square kilometers based on Natural Heritage Program range maps that appear on the Montana Field Guide.
Area of Occupancy
ScoreU - Unknown
ScoreE - Relatively Stable (±25% change)
CommentPopulations declined after European arrival and then dramatically after the introduction of DDT. However, populations have rebounded and are probably best recognized as stable within +/- 25% since European arrival at this point.
ScoreF - Increasing. Increase of >10% in population, range, area occupied, and/or number or condition of occurrences
CommentThe FWP Bald Eagle database documented 280 breeding territories in 2000 and 550 breeding territories in 2010, an increase of 96% over the last 10 years. Similarly, raptor survey routes for Montana between 2000 and 2010 have also shown an increase of 60% over the past 10 years. BBS data for Montana is of lowest credibility and shows an increase of +12.5% per year or 325% increase for the last decade. BBS data for the Northern Rockies is of lowest credibility and shows an increase of +7.2% per year or 200% increase for the last decade.
ScoreF - Widespread, low-severity threat. Threat is of low severity but affects (or would affect) most or a significant portion of the population or area.
CommentEncroachment of human development on nest sites, contaminants, collisions with vehicles at road kill sites, and electrocutions all represent threats to populations in Montana.
SeverityLow - Low but nontrivial reduction of species population or reversible degradation or reduction of habitat in area affected, with recovery expected in 10-50 years.
CommentSpecies seems to be doing well and has shown the ability to recover.
ScopeModerate - 20-60% of total population or area affected
CommentProbably 20-60% of the population is being impacted by threats at any given time.
ImmediacyModerate - Threat is likely to be operational within 2-5 years.
ScoreB - Moderately Vulnerable. Species exhibits moderate age of maturity, frequency of reproduction, and/or fecundity such that populations generally tend to recover from decreases in abundance over a period of several years (on the order of 5-20 years or 2-5 generations); or species has moderate dispersal capability such that extirpated populations generally become reestablished through natural recolonization (unaided by humans).
ScoreB - Narrow. Specialist. Specific habitat(s) or other abiotic and/or biotic factors (see above) are used or required by the Element, but these key requirements are common and within the generalized range of the species within the area of interest.
CommentNarrow Specialist. Need suitable nest sites near riparian foraging areas.
Raw Conservation Status Score
3.5 – 0.25 (population size) + 0.0 (geographic distribution) + 0.25 (short-term trend) + 0.0 (threats) = 3.5
How Scores are Calculated
With a white head and tail contrasting with a dark brown body and wings, the adult plumage of the Bald Eagle, attained at approximately 5 years of age, is unmistakable. In addition to the obvious white head and tail, other distinguishing features include the yellow bill, cere, iris, legs and feet. Second in size of North American birds of prey only to the California Condor (Gymnogyps californianus
), the Bald Eagle ranges in total length from 71 to 96 cm, with an average wingspan of 168 to 244 cm and a body mass ranging from 3.0 to 6.3 kg (Buehler 2000). In general appearance the sexes are similar with females approximately 25 percent larger than males. The plumage of the juvenile birds is much less distinct, being dark brown overall. The head, body, wings, and tail are dark brown with limited mottling on the underside of the wings and on the belly. While the legs and feet of the young bird are yellow like those of adults, the bill and cere are dark gray and the iris is dark brown.
The voice of the Bald Eagle is a weak series of chirps. The vocalization is described as flat chirping, stuttering whistles, given in a halting fashion, with the immature calls generally harsher and more shrill than those of the adults (Buehler 2000, Sibley 2000).
For a comprehensive review of the conservation status, habitat use, and ecology of this and other Montana bird species, please see Marks et al. 2016, Birds of Montana.
In adult plumage, the Bald Eagle is unlikely to be confused with any other species. Juvenile Bald Eagles may be confused with Golden Eagles (Aquila chrysaetos), especially with adult Goldens. A few characteristics differentiate these two species. The Bald Eagle has unfeathered legs, while those of the Golden Eagle are feathered. During flight, the head and neck of the Bald Eagle extend to about half the length of the tail, while the Golden Eagle is considerably less. This distinction is true for all age classes of both species. The terminal tail band on the Golden Eagle is dark and well defined, especially on the juveniles. In addition, the underwing and belly of the Bald Eagle show a greater amount of white compared to the Golden Eagle, whose white feathering is restricted to the base of the flight feathers (Buehler 2000).
Western Hemisphere Range
Summary of Observations Submitted for Montana
Number of Observations:
(Click on the following maps and charts to see full sized version)
Map Help and Descriptions
(direct evidence "B")
(indirect evidence "b")
No evidence of Breeding
(regular observations "W")
(at least one obs. "w")
(Observations spanning multiple months or years are excluded from time charts)
The Bald Eagle is a resident species in the forested, mountainous areas of the state. Other individuals from more northerly latitudes either winter in Montana or migrate through the state to more southerly locations. Residents generally remain in the vicinity of their breeding areas throughout the year, while some, though remaining in the state, may move to the more temperate weather of lower elevations or to other areas with higher concentrations of food (Montana Bald Eagle Working Group 1994). This is especially true of individuals that nest at higher elevations.
Congregations of migrating Bald Eagles may be evident in autumn along the north-south mountain chains with an associated abundance of food sources; numerous eagles have been observed migrating over Rogers Pass and the Bridger Mountains (Hawk Watch International 2003). Large concentrations of eagles have formerly been reported feeding on spawning kokanee (Oncorhynchus nerka) in Glacier National Park and at Canyon Ferry Reservoir, north of Helena, when spawning fish were abundant (Montana Bald Eagle Working Group 1994). In the Bozeman area, birds arrive by November 20 and leave by April 25 (Skaar 1969).
In Montana, as elsewhere, the Bald Eagle is primarily a species of riparian and lacustrine habitats (forested areas along rivers and lakes), especially during the breeding season. Important year-round habitat includes wetlands, major water bodies, spring spawning streams, ungulate winter ranges and open water areas (Bureau of Land Management 1986). Wintering habitat may include upland sites. Nesting sites are generally located within larger forested areas near large lakes and rivers where nests are usually built in the tallest, oldest, large diameter trees. Nesting site selection is dependent upon maximum local food availability and minimum disturbance from human activity (Montana Bald Eagle Working Group 1994). See the Montana Bald Eagle Management Plan (1994) for further details including home range sizes and habitat requirements of fledgling birds.
Ecological Systems Associated with this Species
- Details on Creation and Suggested Uses and Limitations
How Associations Were Made
We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for
vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Foresman 2012, Adams 2003, and Werner et al. 2004);
- Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
- Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use, species that only overwinter in Montana were only evaluated for overwintering habitat use, and species that only migrate through Montana were only evaluated for migratory habitat use.
In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.
However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if
point observations were associated with that system.
Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.
The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.
If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.
Suggested Uses and Limitations
Species associations with ecological systems should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning.
These potential lists of species should not be used in place of documented occurrences of species (this information can be requested at: http://mtnhp.org/requests/default.asp
) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.
Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.
Land cover mapping accuracy is particularly problematic when the systems occur as small patches or where the land cover types have been altered over the past decade.
Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections).
Finally, although a species may be associated with a particular ecological system within its known geographic range, portions of that ecological system may occur outside of the species' known geographic range.
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- Commonly Associated with these Ecological Systems
Forest and Woodland Systems
Wetland and Riparian Systems
- Occasionally Associated with these Ecological Systems
Forest and Woodland Systems
Human Land Use
Wetland and Riparian Systems
The majority of their diet is comprised of fish. Important prey for Bald Eagles are waterfowl, especially in the winter, salmonids, suckers, whitefish, carrion and small mammals and birds (Bureau of Land Management 1986).
The number of birds in January increased from about 260 in 1980 to about 450 in 1984 (Bureau of Land Management 1986). Eagles on McDonald Creek in Glacier National Park increased from a peak of less than 50 in 1939 to a peak of more than 500 (Shea 1973), and have since declined because of a drop in the number of kokanee salmon spawning on McDonald Creek. Fall/winter concentrations have been noted on the Missouri River at Canyon Ferry Dam and at Fort Peck.
The Bald Eagle breeds at approximately 5 to 6 years of age. Nests are often massive structures of branches and sticks with an interior cup lined with grass, pine needles, and plant stems (Baicich and Harrison 1997). Nests may be used year after year, resulting in huge constructions, sometimes up to 12 feet in height and 8 feet in diameter. Most nests are in timber stands, 1.2 hectares with a canopy closure less than 80%. The most common nest trees are ponderosa pine, Douglas fir and cottonwood. The eggs are white, non-glossy, short ovals averaging 71 x 54 mm in size (Baicich and Harrison 1997). The clutch, usually consists of two eggs, but may range from one to three, and is laid in March or April. Incubation, performed by both sexes, lasts about 5 weeks. Mortality for the second young to hatch is high. First flight occurs at 10 to 12.5 weeks. The young are cared for by the adults at this time and may remain around the nest for several weeks after fledging. Adults may not reproduce every year.
Breeding dates in Montana range from March to July (Montana Bird Distribution Committee 2012). Across the state between 1980 and 2014 average nest success per year was consistently between 75 and 80%, with an average of 1.3 to 1.5 young fledged per nesting pair (DuBois 2016).
General objectives of habitat management for Bald Eagles in Montana include: maintaining prey bases; maintaining forest stands currently used or suitable for nesting, roosting, and foraging; planning for future potential nesting, roosting, and foraging habitat; and minimizing disturbances from human activities in nest territories, at communal roosts, and at important feeding sites (MBEWG 1991). The Montana Bald Eagle Management Plan (MBEWG 1994) directs management of this species in the state. Specific objectives identified in the plan include: a minimum of 800 nesting pairs in the 7-state Recovery Area; nesting success rate of 65% in occupied sites over a 5-year period with annual average production of 1.0 fledged young per pair; population goals recognized in at least 80% of management zones with nesting potential; and continued population increases for 5 consecutive years. See the Habitat Management Guide for Bald Eagles in Northwestern Montana (MBEWG 1991) and the Montana Bald Eagle Management Plan (MBEWG 1994) for further details on management guidelines and recovery objectives.
- Literature Cited AboveLegend: View Online Publication
- Dubois, K. 2016. Bald eagle nesting populations and nest monitoring, 1980-2014. FinalReport. Montana Fish, Wildlife & Parks. 27 pp.
- Marks, J.S., P. Hendricks, and D. Casey. 2016. Birds of Montana. Arrington, VA. Buteo Books. 659 pages.
- Additional ReferencesLegend: View Online Publication
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