Breeding birds occur in the north to the limit of the treeline from Alaska including the Aleutian Islands across Canada to Newfoundland. The Bald Eagle is apparently absent from Keewatin, the arctic archipelago, and northern Quebec. In the west, the breeding range extends south through British Columbia to northern California, northern Nevada, and northwestern Colorado. It becomes disjunct further south but populations breed in Arizona, New Mexico, and northern Mexico. East from British Columbia, it breeds in the forested regions of all of the provinces and south into the states surrounding the Great Lakes and vicinity such as Minnesota, Iowa, Wisconsin, Illinois, Michigan, and northern Ohio, Pennsylvania, and New York. Breeding also occurs along the east coast from Maine south to Florida and along the Gulf coast to Texas. The Bald Eagle is generally absent as a breeder throughout the remaining states.
Wintering birds can be found in the Aleutian Islands and along the south coast of Alaska south along the British Columbia coast and inland across the southern one-fifth of the province. Wintering birds can also be found throughout southernmost Canada and south throughout most of the United States but with higher concentrations along the upper Mississippi drainage and sporadically throughout such central states as Colorado, New Mexico, Wyoming, Oklahoma, Kansas, and Nebraska.
Birds can be found year-round in the Aleutian Islands and south along the Alaska and British Columbia coasts to northern California. Inland, the Bald Eagle occurs from about the southern one tenth of British Columbia to northwestern Colorado. Resident birds can also be found in the Great Lakes states, east along the St. Lawrence drainage, and south along the east coast to Florida and Texas.
The Bald Eagle only occurs in North America and two races are recognized. Haliaeetus leucocephalus leucocephalus breeds in the southern United States and Baja California south of an arbitrary 40 degrees of latitude. This race intergrades with H. l. alascanus that occupies the remaining range north to Alaska.
MIGRATION
The movement patterns of the Bald Eagle is complex. The continental picture consists of some seemingly simpler north-south migrations, local movements, post-breeding dispersal north by southern breeders, east-west shifts, and aggregations at significant food supplies followed by movements to other major food sources (in any direction). These, coupled with movements by resident birds, widespread winter population shifts and large winter ranges can make it difficult to analyze patterns based upon isolated observations or limited data.
In some areas, eagles are resident near the nesting locality and return to the nest for roosting. Elsewhere, lack of year-round food or harsh weather force them to migrate. In general, northern breeders tend to go south after the nesting season and some southern breeders (as far north as 49 degrees) move northwards after nesting and move south again during the fall. These northbound birds may arrive in the territories of northerly breeders while young are still in the nest. Recently fledged birds in southern Canada and the northern United States will migrate south in the fall, but their breeding range will be filled with southbound migrants that were fledged in the northern parts of the continent. Thus, areas may be utilized by eagles on a year-round basis, but they are different birds.
Virtually all migration movements are confined within the overall North American breeding range. Migration seems to take place throughout the day, particularly in the fall, with no pronounced peaks or lulls, although some reports indicate increased activity during the afternoon. Local weather and thermal conditions dictate when birds tend to take flight. Flight elevations for some birds are so high that they pass areas largely unnoticed, but most birds probably average between 600 and 1,800 feet (186 and 558 meters) above ground. The average distance traveled by birds in one study in the west was about 60 miles (96 kilometers) per day but one bird traveled 300 miles (480 kilometers) in a single day. The earliest southbound migrants tend to be the young of the year, and in general, they are also the latest to return north. Family units do not appear to function as a group during migration, but rather, travel independently. Adults generally return to their nesting territories and young birds may return to the general vicinity or disperse widely in many directions from the wintering grounds.
To add a touch of confusion, it should be noted that there is much in the way of local movements over a distance of several hundreds of miles that occur as non-breeding bird fly "circuits" over a period of several weeks or months. Fall migration can be protracted as birds visit local food concentrations for varying lengths of time (days or weeks) enroute to the final wintering destination which may not be reached until January or February. Some wintering birds become relatively sedentary with localized movements while others continue a nomadic lifestyle. As well, movements to local food sources such as salmon spawning sites in the Pacific Northwest occur during November and December with departure again during January or February as the food supply dwindles and birds move to local nesting territories, other food sources, or simply start the general migration north. As well, some birds will make tentative northbound movements in the spring of perhaps 100 or more miles (160 kilometers). They may remain at the new site for a few days and then return to the original departure point, only to depart again later in the season. Thus, it is not unreasonable to expect mobile eagles during many or all months of the year somewhere in North America.
During September and October, birds move easterly along the Gulf of Alaska. Presumably not just from areas to the north, large numbers of eagles congregate along the Chilkat River during October and remain until late December. Cold weather and diminished food sources during January cause juveniles and immatures to move south into British Columbia and Washington state. Adult and subadult birds move west to the coast and perhaps northwest as far as Cook Inlet. Adult-plumaged birds arrive on the Chilkat later and stay later than brown-plumaged birds.
Through the Pacific Northwest, there is a complex picture involving resident birds, southbound migrants and birds moving north while others move south. There is a fall southerly movement along the coast fed in part by birds from the interior of British Columbia and western Canada. There is also a movement south throughout the western cordillera as birds visit known food sources enroute to wintering sites such as the Klamath Basin, Idaho, Utah and Nevada. Movements are between October and December. Birds from northern Alberta and the MacKenzie River drainage move into the western interior states primarily during October and November. Birds from parts of north central Canada such as Saskatchewan and Manitoba move into the southern midwest states from October through early February with the Missouri River drainage being a major wintering area. By the end of January or early February, they have reached states such as Arizona, New Mexico, Texas, and Michigan.
Movements through the Great Lakes and northern Mississippi River drainage reaches a peak in late December as birds move into states bordering the river. Some birds from the Great Lakes area and north will however, move westward to the Rockies and eastwards to the Atlantic coast south of Maryland. In the maritime provinces and New England states, some migrants are noted as early as late August with the movements largely finished by late November.
Northbound birds in the west are well in evidence as they pass through the northern tier of states from late February through late March and early April. Birds pass out of New Mexico from early to mid-March and are generally gone by the first of April. Coastal movements seem less-well understood due to the large number of resident birds that are difficult to separate from migrants. Recently-fledged birds in the Pacific Northwest can be heading in a northerly direction to food sources in Alaska and northern Canada by August. A large concentration of eagles occurs on the Stikine River during April with birds probably coming from Alaskan wintering grounds as well as more southerly wintering areas. Young California birds in their first summer-fall, move north to other food sources and then south again later in the year. From the western interior states, wintering birds move along the eastern foothills of the Rockies and on into the MacKenzie and other drainages. This movement passes the Canadian border during March and April but non-breeding birds are still moving northwards in the Northwest Territories as late as early August. The adults move in a fairly direct fashion but immatures tend to wander more erratically northwards and include some east-west wanderings in their migration.
Spring migrants in the central portion of the continent leave the southern United States during March and April and are back in Saskatchewan beginning in March. Northern passage through the Great Lakes occurs from February through May and March through April for the northeast states and maritime provinces. Recently fledged birds depart north from Florida from late March through May, dispersing along the Appalachian chain and inland along waterways and lakes. Movement can be rapid as some birds have arrived in Canada only one month after leaving Florida. The pattern of moving north after breeding occurs in birds as far north as Chesapeake Bay and is not restricted to the most southerly breeders in the United States.
In some wintering areas, particularly the Pacific Northwest and Alaskan coasts, movement during the winter months is noted in relation to the patterns of aquatic food supplies. Typically, eagles move onto salmon bearing streams during late November, December and January to take advantage of late spawning species of pacific salmonids. The peak numbers on many of these streams occur during January with steady and at times rapid declines noted through February and March. Some rivers such as the Skagit, Skykomish and Columbia in Washington State, or the Fraser and its tributaries in British Columbia penetrate considerable distances into the interior areas. Birds wintering in more inland sites may simply depart northwards from there during the early spring. From other rivers, they may migrate westward to the coast and thence north to the breeding territories. Elsewhere, winter movements may not be on the scale of the coastal shifts, but birds may travel over large winter ranges that can reach 600 square miles (1,554 square kilometers).
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