SPECIES

Bald Eagle Haliaeetus leucocephalus Scientific name definitions

David A. Buehler
Version: 2.0 — Published October 7, 2022

Movements and Migration

Dispersal and Site Fidelity

Natal Philopatry and Dispersal

There are few data on the relationship between natal site and breeding site, because of the prolonged immature stage (4+ years). The most comprehensive analysis from banding data included 878 individuals from the coterminous United States that were banded as nestlings and recovered as adults during the breeding period (presumably near their nesting areas; 145). Mean dispersal distance was 69.2 km and did not differ across the 8 geographic regions of the study; median dispersal distance of females (138.2 km) was over twice that of males (59.8 km) (145). Five of eight males (63%) that were color-marked in the Greater Yellowstone Ecosystem nested in the same area (mean = 60 km from natal site); the other three males nested up to 328 km away in Montana; three color-marked females all nested in Greater Yellowstone Ecosystem (146). Four marked adults in Saskatchewan nested within 25 km of their natal territory (147). Nine of 46 birds (19.6%) hatched in Texas and observed to adulthood nested in Texas, whereas two adults nested in Arizona and Mexico (46).

Florida immatures that summered on the Chesapeake Bay showed high summer-site fidelity (DAB).

Adult Fidelity to Breeding Site and Dispersal

Color-marking and banding data suggest that breeding site fidelity is very high (148, 149, 150). Nest site fidelity was high in a color-banded population in California, with two individuals using the same nest site for up to 10 years and six individuals using the same nest site for at least 6 years (149). One marked female in Saskatchewan nested at the same site for 13 consecutive years (until end of study; 147). One unmarked female in Ohio used the same nest site over a 9-year period (151). A male in Kansas occupied the same territory for 29 years (150).

Fidelity to Overwintering Home Range

Adults breeding in northeastern portion of range and wintering on Chesapeake Bay showed high winter-site fidelity; however, home ranges were large (DAB). Ten of 36 (27.8%) color-marked immatures and adults wintering in Colorado were repeatedly found in the same area during winter, and the actual number returning was higher when marker loss was factored in; one individual wintered in same area for 10 years (152). In Maine, 17% of 135 banded individuals photographed during one winter at a supplemental feeding site were photographed the next winter; the actual return rate was greater because some birds that returned in the second winter did not get photographed (3).

Migration Overview

The Bald Eagle has a complex pattern of migration that varies with age (immature versus adult), location of breeding (north versus south, interior versus coastal), climate of the breeding site (especially during winter), and winter food availability at the breeding site. The migration strategy of adults (non-migratory versus migratory) and immatures (directed migration versus dispersal) varies between populations (153). Individuals generally migrate alone but occasionally join other individuals, but does not form kettles or flocks. Concentrations of migrants can occur at exceptional locations for feeding and roosting. The timing of migration in some populations appears to be changing in response to climate change. Fall migration at Whitefish Point, Michigan has been increasingly delayed over the last 40 years, at a rate greater than 8 days per decade, but spring migration at Hawk Ridge, Minnesota has been stable (154).

Timing and Routes of Migration

Fall

Northern individuals (those breeding north of 40°N) in interior populations, including Alaska, generally migrate south from August into January, with immatures departing breeding grounds first and migrating farther south (see Figure 1). In Pacific Northwest, Alaska, and some parts of the intermountain west, migratory movements coincide with salmon (Oncorhynchus spp.) migrations. For example, immature and adult eagles from the Pacific Northwest migrate north along the coast as far as the Chilkat River, Alaska, in late summer to take advantage of the earliest salmon runs (155; Figure 2). Adults and immatures from Alaska and the Pacific Northwest then follow the salmon runs south down the coast, with adults arriving at Pacific Northwest wintering grounds during November and December and immatures arriving in January (155, 156, 120). In the western United States (e.g., California and Glacier National Park, Montana), some immatures migrate north and west to spend fall and winter in coastal southeastern Alaska and the Pacific Northwest, again following salmon runs (157, 158). Adults and immatures from Northwest Territories, Alberta, and Saskatchewan migrate south through the intermountain region from September into December, formerly with stopover at Glacier National Park in fall to feed on salmon carcasses (159). Stopover counts at Glacier National Park peaked in 1981 at 639 but the concentration disappeared by 1991 because of the decline of the salmon population (160). Similar fall concentrations (peak counts > 300 eagles) associated with kokanee salmon (Oncorhynchus nerka) runs occurred during the 1990s at Hauser Reservoir, upper Missouri River, Montana (121). Immatures from the greater Yellowstone ecosystem migrate westward along the Snake River into Idaho or northern Utah, and then moved to the Pacific Coast for winter (146). Migrants from Saskatchewan winter in a broad portion of the southwestern United States, from California to Texas and Missouri (161, 13, 162). Juveniles from northern California tracked by satellite dispersed northward to British Colombia and the Northwest Territories in their first summer before returning to California during fall and winter (163). Adults in some northern populations may not migrate but instead shift locally based on winter food sources (e.g., greater Yellowstone ecosystem; 157). Six adults equipped with satellite transmitters tracked through 16 fall migrations moved south from Manitoba and Ontario into the upper Mississippi River valley from 4 September to 19 December (median 25 October; 164). Some Bald Eagles in Great Lakes region and adjacent areas in Canada migrate eastward to winter on Atlantic Coast from Maine to New Brunswick to Chesapeake Bay (165, 166). Migrants from the northeastern United States and Canada move south along the Atlantic Coast or migrate inland along the Appalachian Mountains (167). Juveniles equipped with satellite transmitters departed Labrador from 7 October through 12 November (median date 26 October) for the Gulf of Saint Lawrence; one juvenile stayed there to winter, while four others continued onward to wintering areas from Connecticut to Chesapeake Bay and West Virginia (168). At hawk watches in Appalachians of Pennsylvania, the majority of migration occurs from late August through early December, with peak adult movement during the first two weeks of September and peak immature passage at variable times between second week of September and second week of November (169). Adults that breed in coastal Maine remain in that vicinity as long as open water is available (170).

Southern adults (those breeding south of 40°N) usually do not migrate but remain year-round in the vicinity of the nest site (171, 165, 172, 173). Those southern immatures that migrated north in spring or summer return southward from August to December (171, 165, 173). Some Chesapeake immatures (< 10%) move south of the bay from December into February (165). Juveniles and subadults equipped with satellite transmitters that migrated north from Florida breeding areas in spring, moved back south to Florida from late July to late December, with no difference in the timing of southward migration between juvenile and sub-adult age classes (174).

Based on long-term monitoring data from seven raptor monitoring stations in eastern North America, the phenology of fall migration has not shifted with changes in climate parameters, unlike numerous other raptor species (175).

Spring

Northern Bald Eagles return to their breeding grounds as soon as weather and food availability permit, generally from January to March. Bald Eagles wintering in the upper Mississippi Valley tracked by satellite migrate northward from mid-January to late March (median date = 4 March; 164). Spring migration is more directed and shorter in duration than fall migration in Colorado (125), but spring and fall migration are of similar duration in the Great Lakes region (164). Adults and immature birds in California were tracked via satellite during late February and March as the moved northward to summer/breeding areas in Alberta, Saskatchewan, and Northwest Territories (163). There was no difference in departure date based on sex in radio-tagged adults that wintered in Colorado's San Luis Valley, with eagles leaving the valley from 11 February to 1 April (176). Four immatures tracked by satellite departed their wintering grounds in the eastern United States during mid-March, and arrived on the north shore of the Gaspe, Quebec in mid-April, with an average migration duration of 32 days (177). Two of these immatures then continued northward to the Quebec–Labrador border (their natal area), arriving by mid-May.

Though southern adults tend to be resident, many juveniles and immatures migrate or disperse. Most Florida-raised juveniles and sub-adults move northward along coastal areas, inland along the Appalachian Mountains, or (rarely) up the Mississippi River as far as the Great Lakes region, with juveniles departing breeding grounds from April into June and subadults leaving from March into August (171, 173, 174, 178). Some Florida immatures do not migrate but move locally among feeding sites (172). One South Carolina immature tracked by satellite moved northward in spring along the coast to Maine but returned via the Appalachians (179). Immatures in Texas also migrate northward beginning in April, with most moving up the Mississippi River valley, but some heading west into the intermountain region, and others moving to the Atlantic Coast (46). Juvenile from Arizona with VHF transmitters, tracked from early June to late July, went as far as Manitoba's Lake Winnipeg and Washington's Puget Sound (180). Most immatures on Chesapeake Bay limit movements to the bay; < 10% of radio-tagged immatures moved north in summer to Maine (165).

Migratory Behavior

Typically migrates from around 10:30–17:00 h (125, 176), when thermals that occur during the heat of the day allow migrating eagles to limit their energy expenditure by repeatedly soaring upward on thermals and then gliding downwards and forward. Some migrants circle continuously on thermals while using prevailing winds to move in the desired direction (181). Bald Eagles also take advantage of orographic lift, associated with updrafts along ridgelines and mountains, to facilitate migration (182). Migration routes may include major river systems (e.g., Mississippi River ; 164) or major mountain chains (e.g., Appalachian Mountains; 174), as well as Pacific (163) and Atlantic ( 174) coastal areas. Limited information suggests that pairs migrate independently but may winter together (125, 176). Migration to breeding grounds may be more rapid than migration away from breeding grounds, similar to most other species, as arriving early in breeding areas may provide an advantage when competing for nest sites and mate. This was not the case in one satellite telemetry study where spring migration appeared to last longer (164). Adults migrating northward to breeding territories in Saskatchewan, Alberta, and Northwest Territories move in almost a direct line with little deviation while immatures show considerable route deviation (125, 123). Adult males breeding in Saskatchewan depart wintering grounds in Colorado prior to their female mates (125). Migration speeds ranged from 25 to 33 km/h in light winds near Saskatoon, Saskatchewan (181), but averaged 50 km/h over the entire migration route, with a peak of 144 km/h (125). Two radio-tagged adults tracked from San Luis Valley of Colorado to Saskatchewan flew 2,000 km in 15 days, thus averaging 133 km per day (176). Other radio-tagged migrants from San Luis Valley averaged 180 km/d (125), similar to the 202 km/d average for one individual tracked via satellite from Arizona to Northwest Territories, Canada (183). The mean altitude of migrants has been estimated by ground observers at 1,500–3,050 m above ground (125). Four adults tracked by fixed-wing aircraft in Montana averaged 98 km/d during spring migration and migrated at 200–600 m above ground (123). Adults tracked via satellite telemetry flew a total distance of 1,655 km ± 526 SD, on average, between breeding and wintering areas (164). The duration of fall migration averaged 51 d ± 19.8 SD, whereas spring migration averaged 67 d ± 48.4 SD (164). Juveniles tracked from Saskatchewan moved 33 km/d at an average speed of 26 km/h and altitudes estimated at 54–180 m above ground (184). Juveniles moving northward post-fledging in California migrated during the warm times of the day that are associated with thermal activity and averaged 162 km/d at altitudes estimated at 200–500 m above ground (158). Sibling juveniles on Chesapeake Bay showed no more similarity in timing and nature of migratory movements than did unrelated juveniles (DAB). Migrants arrive on Missouri wintering grounds well after arrival of waterfowl, suggesting that southward migration does not necessarily coincide with food availability on the wintering grounds but rather the disappearance of food on the breeding grounds. Conversely, migrants depart northward in spring at times when food availability is increasing, so that the timing of spring migration is not linked to food availability on wintering grounds (185).

Control and Physiology of Migration

Largely unknown. Radio-tagged individuals departed Colorado wintering grounds 5 hours after sunrise on days when the winds were from the west-southwest, skies were cloudy, and temperatures were greater than had been on previous days (125, 176). Northbound spring migrants in Saskatoon, Saskatchewan were observed most often when temperatures were increasing and winds were out of the south or southwest (181). Adults were not observed foraging during their northward migration from Colorado to Saskatchewan (about 2,000 km), leading to a weight loss of up to 25% (125, 176). Other studies have suggested that migrants forage opportunistically en route (123), although foraging by adults during spring migration may be limited. Immatures are more apt to feed opportunistically for prolonged periods (i.e., days) to support spring migration. Undesirable winds and inclement weather can cause deviations from the flight path and prolong stopovers. Adults arrive on breeding grounds in Saskatchewan when all lakes and most rivers are still frozen over and foraging opportunities are limited (125, 176). Immatures arrive later, presumably when foraging opportunities increase and can be exploited by the less-experienced and less-skilled immatures.

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Bald Eagle

Haliaeetus leucocephalus

Abundance

Estimates of relative abundance for every week of the year animated to show movement patterns. Relative abundance is the estimated average count of individuals detected by an eBirder during a 1 hour, 1 kilometer traveling checklist at the optimal time of day for each species.   Learn more about this data

Relative abundance
0.01
0.11
0.65
Week of the year

Recommended Citation

Buehler, D. A. (2022). Bald Eagle (Haliaeetus leucocephalus), version 2.0. In Birds of the World (P. G. Rodewald and S. G. Mlodinow, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.baleag.02