Bald Eagles aren’t hairless, so why are they called bald? The name comes from an older meaning of the word "white-headed", referring to the white head feathers of adult birds that contrast with their darker body.
The bald eagle builds some of the largest nests of any North American bird, sometimes up to 8 feet (2.4 m) wide and deep. The same nest may be used for several years in a row, becoming larger as new material is added each year.
Bald eagles are sexually mature at the age of four to five years and are early breeders. They often build or reinforce their nests by mid-February, lay eggs in late February, and incubation typically occurs from mid-March to early May. Eggs hatch from mid-April to early May, and the young fledge from late June to early July. Eagles typically produce one to three eggs per year, with two being the most common.
A young eaglet can gain as much as 170 grams (six ounces) per day — the fastest growth rate of any bird in North America. Eaglets typically fledge between eight and 14 weeks of age but remain near the nest, continuing to rely on their parents for food and guidance for about six more weeks. They usually begin flying around three months old.
Not all eagle eggs hatch, and the death rate of young eagles is high. Stronger siblings often kill or cause the weaker ones to die of starvation. Losses due to exposure, diseases, parasites, and predation can also occur while the young are still in the nest.
More than 90 per cent of eagles that fledge do not survive to adulthood. Nearly 60 per cent die during their first year, usually due to starvation, disease, or human causes.
Young bald eagles undergo as many as six plumage changes before getting their adult plumage at about five years of age. Juvenile bald eagles are generally mottled brown or nearly black and resemble adult golden eagles. These juveniles have no distinct white patches. Their tail and wings are mottled brown and white on the underside, in contrast to the characteristic white patches under the wings and the white-banded tail of juvenile golden eagles.
While they are no longer considered an endangered species, continuing threats to bald eagle populations include lead poisoning from shot prey, collisions with motor vehicles, and development-related destruction of shoreline nesting and foraging habitats.
NIWRA, a non-profit organization, is situated in Errington, B.C. We are open to the public daily for viewing of non-releasable animals. Please visit our website at www.niwra.org to learn more about our programs, read stories about our animals, and learn how you can help care for wildlife.
Moira Rosser-Peterson works at the North Island Wildlife Recovery Centre
