Bald Eagle Fact Sheet

Index

Bald Eagle Biology

MORPHOLOGY

Eagles are a member of the Accipitridae family, which also includes hawks, kites, and old-world vultures.

There are two subspecies of Bald Eagle:

1) Southern (Haliaeetus leucocephalus leucocephalus) breeding south of 40^o latitude

2) Northern (Haliaeetus leucocephalus alascanus) breeding north of 40^o latitude

SIZE

Northern Bald Eagles tend to be slightly larger than the southern populations. In the north, females weigh 4.5 - 6.5 kg (10-14 lbs) and males are slightly smaller at 3.5 - 4.5 kg (7.7-9.9 lbs). In the lower Great Lakes, data show that female hatch year eaglets weigh between 3.0 and 3.6 kg (6.6-7.9 lbs) and males range from 4.1 to 4.9 kg (9-10.8 lbs). On average, adult Bald Eagles have a huge wingspan that ranges from 1.8 to 2.2 metres (6 - 7 ft) and the birds are 0.6 -1.0 metres tall (2 - 3 ft).

COLOUR

Juveniles look quite different from adults, and are sometimes mistaken for Golden Eagles (Aquila chrysaetos) at first glance. However, Golden Eagles are slightly larger than Bald Eagles and have brownish feathering all over their bodies. Juvenile Bald Eagles are more similar to the Golden Eagles as they have both brown and white feathers covering their bodies and have a black bill. Bald Eagles reach maturity at four or five years of age, at which time the plumage changes to a blackish-brown back and breast, white head, neck and tail, yellow legs, and a yellow bill.

FEATHERS

Eagles have more than 7,000 lightweight and extremely strong and flexible feathers covering their body. This large number of feathers assists in regulating the birds core temperature (i.e. cool in the summer and warm in the winter) and enable eagles to soar gracefully, and to skilfully manoeuvre after prey. Aside from assisting in flight, eagle feathers garner significant spiritual and ceremonial characteristics for First Nations peoples.

LIFESPAN

In the wild, Bald Eagles can live as long as 30 years. However, the average lifespan is closer to 20 years. Bald Eagles in southern Ontario appear to have a shortened lifespan of 12 years or less. The oldest known Bald Eagle was a captive eagle in West Stephentown, New York that lived to be almost 50 years old. Juvenile eagles have varied survival rates during their first weeks, months, and year of life. A Chesapeake Bay study (Buehler et al. 1991) reported 100% survival of 39 radio-tracked juvenile eagles. Comparatively, Wood et al. (1998) found that a minimum of 63% (n=44) of juvenile eagles survived their first year. Smaller scale studies have also reported diverse survival rates. Hodges et al. (1987) reported only 50% (n=8) survival of their radio-tracked juvenile Alaskan population, whereas in Central Labrador, 100% of tagged juvenile eagles survived their first year (Laing et al. 2003).

MATING and NESTING

Bald Eagles mate monogamously for life. However, if one of the pair dies, the survivor will accept a new mate. Bald Eagle pair bonding occurs on either the wintering or breeding grounds. Once a pair selects a breeding territory, they commence nest building. Bald Eagle nests are massive structures, which consist of branches, sticks, moss, and even obscure materials such as hay and twine. Nests are typically built in the top of the most dominant tree within an established territory. In some parts of Canada, Bald Eagles nest in more unusual locations, such as on large rock pinnacles and hydro-towers. Nests are typically 3-4 metres deep and more than two metres wide. Broley (1947) reports that the largest Bald Eagle nest was an amazing 20 ft (6.1m) deep and more than 9 ft (2.8m) wide.

Eggs are laid two or three days apart and are then incubated for 35 days. When the eaglets hatch out they are covered with a very light grayish down and are capable of very limited locomotion. Daily weight gain averages 116g/d (Bortolotti 1984) and they reach their maximum growth at approximately 3-4 weeks of age. Eaglets remain in the nest for about 70 days, during which time the parents deliver food to the nestlings. After leaving the nest, the young eagles usually remain within the natal area for a few weeks because they are still dependent on their parents for some prey provisioning. Juveniles are not efficient hunters when they are first beginning to fend for themselves. During their first few months of independence juveniles will often scavenge dead prey, and use these opportunities to practice their hunting skills.

In southern Ontario, Bald Eagles favour nesting territories near large water bodies and nest in a variety of tree species, including: Sycamore (Plantanus occidentalis), White Pine (Pinus strobes), Black Maple (Acer nigrum), Cottonwood (Populus deltoids), and Red Oak (Quercus rubra). The most frequent tree type chosen here is white pine, with nest heights averaging 21 metres (64 ft).

FOOD HABITS

Eagles feed primarily on fish, mammals, and aquatic birds, but will scavenge dead prey when necessary. Adults are more likely to hunt live prey, whereas younger birds tend to rely more on piracy and scavenging. Bald Eagles will attempt to obtain food by whatever means possible, including stealing from other birds (e.g. will chase and steal fish from Ospreys) or even scavenging fish killed through hydro turbines, or even road killed deer. Most eagles choose a nest site close to an open waterway so that food is readily available.

When hunting from the wing, eagles will travel at a mid altitude of 17-34 metres (50-100 ft) above the ground and will dive feet first to capture prey. A typical hunting sequence involves hunting over water until prey is spotted. The eagle will then dive feet first into the depths of the water, latch onto its prey with its talons, pull the prey out of the water and then carry it to a perch, sandbar, or nest to eat.

In southern Ontario, a variety of prey items are found in and below nest sites. Based on these prey remains, it appears that eagles here are feeding on several different fish species (e.g., Carp- Cyprinus carpio, Sheeps Head-Aplodinotus grunniens, Smallmouth Bass-Micropterus dolomieui dolomieu), turtles (Map Turtle-Graptemys geographica, Painted Turtle-Chrysemys picta marginata) and even some bird species (e.g, American Crow-Corvus brachyrhynchos).

DISTRIBUTION and MOVEMENTS

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. Bald Eagles are also found in the Boreal Forest from Alberta, Saskatchewan, and Manitoba to northwestern Ontario. Bald Eagles are also found in Southern Ontario, Quebec, and the Atlantic provinces. The Gulf of St. Lawrence has been identified as an important stopover area for migrating eagles and Baddeck, Cape Breton is home to numerous gregariously 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.

Eagles may remain in their breeding habitat year round if ample food resources are available and the waterbodies remain ice-free. However, most eagles will move in search of open water and favourable foraging habitats. They will utilize river valleys, tributaries, lakes, coastlines or any other open water habitat which may contain popular food items. Although these birds will feed gregariously, they often hunt and migrate independently.

Different eagle populations migrate along different flyway pathways. The eastern population travels south in the fall and north in the spring along the eastern coast of North America and uses the Gulf of St. Lawrence as a significant stopover site. Western populations, when migratory, travel along the west coast and avoid crossing over large bodies of water. Birds Studies Canada (BSC) hopes to reveal the migratory patterns of southern Ontario Bald Eagles with the new project, Destination Eagle.

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