Bald Eagle Biology
Species: Bald Eagle, Pygargue à tête blanche
Status: Special Concern (Ontario)
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
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.
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
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
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