Bald Eagle Biology

 

Species: Bald Eagle, Pygargue à tête blanche
Haliaeetus leucocephalus
Status: Special Concern (Ontario)

Description

Length: 0.6-1.0 metres (2-3 ft)
Wingspan: 1.8-2.2 metres (6-7 ft)
Weight: males 3.5-4.5 kg (7.7-9.9 lbs), females 4.5-6.5 kg (10-14 lbs)

Adults: Blackish-brown body and wings; distinct white head, neck and tail; yellow legs and bill.
Juvenile: Predominantly brown with varying amount of white mottling underneath, black bill. Can be confused with Golden Eagles (Aquila chrysaetos) which are dark overall or with white restricted to base of tail and flight feathers in young birds. Reach maturity at 4-5 years.

Lifespan

Wild Bald Eagles can live up to 30 years, though 20 years is more typical. The southern Ontario population appears to have a shortened lifespan of 12 years or less, possibly due to the persistence of pollutants in the food chain. Survival rate of juveniles in their first year is variable, and depends on food and habitat availability.

The oldest known Bald Eagle was a captive eagle in West Stephentown, New York that lived to be almost 50 years old.

Distribution and Movement

Map courtesy of Birds of North America Online

The Bald Eagle is found only in North America. The majority of Canada's breeding Bald Eagle population is found in British Columbia, especially along the coast where eagles follow the Pacific salmon runs north. The Gulf of St. Lawrence has been identified as an important stopover area for migrating eagles, and Baddeck, Cape Breton is home to numerous feeding eagles in spring and fall. Newfoundland and Labrador have healthy populations of eagles, which disperse from breeding grounds between mid-October and the first week of November, later than the rest of Canada.

Bald Eagles move nomadically outside the breeding season, taking advantage of food resources wherever they find them. They may congregate at food sources, but tend to live fairly independently. Movement patterns of Bald Eagles are being studied through Bird Studies Canada's project Destination Eagle.

Mating and Nesting

Bald Eagles are socially monogamous, and tend to re-nest with the same mate from year to year. However, if one member of the pair fails to return to the breeding territory, the remaining bird will accept a new mate.

The nests are massive structures made primarily of branches, but other materials such as moss, hay, and twine may also be used. They are generally around three to four metres deep and more than two metres wide, and are typically built in the top of the most dominant tree within an established territory. Nests may also be built on large rock pinnacles and hydro towers. Bald Eagles prefer to nest near water bodies.

Eggs are laid two or three days apart and are then incubated for 35 days. Newly hatched eaglets are helpless, and are covered with a very light greyish down. Weight gain happens quickly though, averaging 116 grams per day (Bortolotti 1984), and they reach their maximum size within three months of hatching.

Eaglets remain in the nest for about 70 days, during which time the parents supply food. After leaving the nest, the young eagles usually remain in the natal area for a few weeks, continuing to be fed by their parents while they learn to fend for themselves. During their first few months of independence, juveniles practice their hunting skills and often scavenge dead prey.

Food Habits

Bald Eagles feed primarily on fish, but also eat small mammals and other birds. They are opportunistic feeders, and will acquire food by hunting, scavenging, or even stealing from other raptors if necessary. Juveniles are more likely to scavenge or steal food, as their hunting skills are still in development.