Bird of the Month: Bald Eagle
By Andy McCormick
PC: Mick Thompson (Bald Eagle)
Scientific Name: Haliaeetus leucocephalus
Length 31 in
Wingspan 80 in
Weight 9.5 lb
AOU Band code BAEA
One of eight species of sea eagles in the world from the genus Haliaeetus from the Greek aliaetos, the sea eagle. It is named for its white head; again from the Greek - leukos, of the color white, and kephale, head. Its common name refers to a Middle English interpretation of balled meaning shining or white (Holloway, 2003). The adult Bald Eagle is unmistakable with its large white head and tail contrasting with its dark brown, bulky body. The bill and eyes are yellow. It soars on wide flat wings and flies using slow, heavy and powerful wingbeats. Its call is surprisingly weak for such a large bird. Various authors describe it as thin and hollow (Alderfer), flat (Sibley) and a mixture of squawks and shrieks ( Bell & Kennedy). Immature birds lack the white head and tail and develop through four stages reaching full maturity in their fifth year. The juvenile through fourth-year birds have varying amounts of white in the belly and underwing coverts and axillaries.
Coastal Bald Eagle migration will follow the salmon runs. Some Pacific Northwest birds will fly north in late summer to catch early salmon migrations and then joined by Alaska birds will follow the salmon south and winter in the Pacific Northwest beginning in November. Fish are their preferred food especially while nesting, but they are opportunistic hunters and will snag an array of fish, waterfowl, and mammals with their talons while in flight. They are quite adept at kleptoparasitism and will steal kills from other raptors particularly osprey. Carrion also makes up a portion of their diet.
Bald Eagles nest in an aerie, a large nest near the crown of very large trees or on rocky pinnacles. Built with sticks the nest will be reused for several years growing larger each year. An old eagle nest can be huge; weigh hundreds of pounds and measure 8-10 feet in diameter. They are sometimes used by Great Horned Owls. The nest of sticks is lined with grasses, moss and sod. The clutch is usually two dull white eggs, which are incubated by both adults for about 35 days. Juvenile birds make their first flight in 10-12 weeks.
Human beings have been the greatest source of mortality for Bald Eagles. They have been killed as perceived threats to livestock and for their feathers for ceremonial purposes. Pesticides caused egg shell thinning and eagle populations plummeted from the 1960s to 1980s. Diligent conservation efforts have been very successful and Bald Eagles are now nesting in every state and the bird has been removed from the Endangered Species list. The species has developed more tolerance to human activity and birds are now seen in inland waterways near cities.
A variety of audio and video recordings of Bald Eagles can be found at the Cornell Lab of Ornithology Web site. Cat# 4334 has a good variety of calls.