A 10% Chance of Survival for Eagle Fledglings
- Moira Rosser-Peterson
- Jul 2
- 2 min read
~wildlife education~
Photo credit: istock.com/BrianEKushner
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, egg laying is often in late February, and incubation is usually mid-March to early May. Eggs hatch from mid-April to early May, and the young fledge from late June to early July. Eagles produce one to three eggs per year; two are typical.
A young eaglet can gain up to 170 g (6 oz) a day, the fastest growth rate of any North American bird. The young fledge anywhere from 8 to 14 weeks of age but remain close to the nest and are cared for by their parents for another 6 weeks. They learn to fly at three months of age.
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% of eagles that fledge do not survive to adulthood. Nearly 60% 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 generally are 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.
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