Bird Fact Friday – the Bald Eagle

Adapted from pages 94-95 of Wildlife of the Arctic

The Bald Eagle is a magnificent bird, the Nearctic equivalent of the White-tailed Eagle. Adults have a white head (the origin of the name) and white tail, but are otherwise dark brown, with a pattern of scalloping from pale feather tips. Sexes are similar. Juvenile eagles do not acquire the adult coloring until they are 3-5 years old. In early young immatures there is a significant amount of white in the plumage which aids distinguishing the birds from adult Golden Eagles. Northern birds are larger than their cousins of the souther US states, the two being considered sub-species.

This bird is piscivorous but an opportunistic feeder, taking both terrestrial and aquatic mammals (e.g. hares and muskrats) as well as birds (primarily waterfowl and gulls). They also feed on carrion and are not infrequent visitors to garbage dumps in Alaska. They hunt both by flying slowly over probable prey sites and from perches, and will pirate food from other Bald Eagles, as well as from Osprey and herons, both of which are, in general, better at fishing but cannot defend themselves against the eagles. They also makes piratical attacks on Peregrines and even on Sea Otters and Coyotes.

Bald eagles nest primarily in trees, and often re-uses nests which may actually be refurbished prior to the birds migrating as well as when they return to the breeding site. One nest known to have been used continuously over several decades grew to be almost 3m in diameter and over 3m high and weighed an estimated 2t: the tree then blew down in a storm. In areas where trees are absent, they will nest on cliffs or even on the ground provided the site is elevated to give the incubating bird good visibility. 1-3, but usually 2, eggs are laid. Asynchronous hatching means first chick hatched usually outcompetes later hatchlings which may die of starvation. 

An adult Bald Eagle at nest. Photo credit: Richard Sale & Per Michelsen.

The Bald Eagle is the emblem of the United States, which made it even sadder when numbers declined sharply as a result of subsidised shooting and the widespread use of organochlorines in the continental US. In Alaska the use of pesticides was minimal, but a bounty on eagles set in 1917 – the result of lobbying by fishermen and fox trappers – was not lifted until 1953. Although the bounty led to ill-advised slaughter, the state remained a stronghold of the species and continues to do so. Once hunting and DDT were banned the population recovered quickly: in Alaska the population increased by about 70% between the late 1960s and the late 1990s. Alaska and the Canadian province of British Columbia are the strongholds of the species with the population now probably close to the carrying capacity of the environment.

Bald Eagles breed in central and southern Alaska, including the Aleutians, and across North America, but rarely north of the timberline. In winter the birds move to the continental United States, though birds in southern Alaska are resident.

Wildlife of the Arctic
By Richard Sale & Per Michelsen

Wildlife of the Arctic is an accessible and richly illustrated pocket-sized photographic field guide to the birds, land and sea mammals, and plants and lichens of the northern polar region–including Alaska, Canada, Greenland, Iceland, Scandinavia, and Russia. Written and illustrated by naturalists with extensive Arctic experience, this handy book features detailed facing-page descriptions of each species, including information about identification, range, distribution, and breeding and wintering grounds. A substantial introduction explains the area covered, with information on the poles, geology, snow and ice, auroras, and the influence of global warming. This portable, user-friendly guide is the perfect companion for birders, ecotourists, and cruise-line passengers visiting the Arctic Circle and other areas of the far north.

  • An accessible and richly illustrated pocket-sized photographic field guide to Artic wildlife
  • Features more than 800 color photos illustrating more than 250 bird species, 60 land mammals, and 30 seals and whales
  • Includes extensive facing-page species descriptions and identification information
  • Provides an overview of the Arctic region, with information on the poles, geology, snow and ice, auroras, and the influence of global warming
  • Explores each family of birds and mammals, and has sections covering fish, insects, plants, and lichens
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