Eagle Facts

About the Bald Eagle (Haliaeetus leucocephalus)

On June 20, 1782, the bald eagle was officially adopted as the national emblem of the United States of America. Native only to North America, they may be found as far north as Alaska and as far south as the Florida Keys. The bald eagle ranges in length from 34 to 43 inches, with a wingspan as great as 7 1/2 feet. Males range in weight from 8 to 10 pounds, while the larger females weigh 10 to 14 pounds. Contrary to myth, the eagle is unable to lift more than four pounds. Immature birds show variable grayish-brown and white plumage, with dark eyes and beaks and yellow legs. By 4 or 5 years of age, adult birds have the distinctive white head and tail with yellow eyes, beaks and legs. The average lifespan for a bird in the wild is 25 to 30 years.

Reproduction/Nesting

The bald eagle reaches sexual maturity at 4 to 6 years of age. Breeding in Canada and northern New England begins in March and may continue into August. Pairs tend to mate for life; although if one of the pair dies, the survivor will take a new mate. Elaborate courtship rituals involve spectacular aerial displays including chases, undulating flights and interlocking cartwheels.

The pair gathers large branches and sticks to build a basket-like nest, with the male doing the bulk of the foundation work. Nests are lined with grasses, pine needles, feathers, mosses and rushes. They are typically constructed in the tallest live tree at the edge of a lake or river, and are rebuilt and added to each year. Nests average eight feet wide at the base and six feet in height. A clutch consists of one to three dull, white eggs which hatch in approximately 35 days. Both male and female birds incubate eggs and care for the young. The young remain in the nest for 10 to 12 weeks before fledging.

Eggs

A bald eagle egg is slightly smaller than a domestic goose egg. The chick will measure 4 to 5 inches at hatching and weigh only a matter of ounces.

Bald eagles incubate their eggs for about 35 days. They begin incubation as soon as the first egg is laid. The second egg usually appears within 36 to 72 hours after the first. Occasionally a clutch of 3 eggs will be produced.

Chicks

Eagle chicks are fed a steady diet of fish, occasionally supplemented by water fowl (ducks, geese) or water birds (gulls, cormorants). About 85% of a chick's diet will typically consist of fish such as carp, white sucker, shad, bullhead and sunfish. The adults capture and tear the fish into small strips, offering them to the chicks. The chicks snatch the food from the adult's beak and swallow it whole. An eagle chick will eat as much as it can at a single feeding, storing food in its crop. The crop, an organ located near the base of the bird's neck, will enlarge as it fills, resembling a golf ball.

Hunting and Feeding

Bald eagles feed primarily on fish, birds (especially water fowl) and on rare occasions small mammals. They use a wide variety of foraging techniques including hunting and killing prey, stealing prey from others and scavenging on dead carcasses. They grasp their prey with their sharp talons, while the beak is used solely for tearing flesh.

The male does most of the hunting and scavenging during the early weeks of the chick's life. The female does the majority of the feeding and brooding. The male will often eat the head of the fish he catches and then bring the remainder to the nest. The male will brood and feed the chick when the female is off the nest. She will leave to stretch, defecate, bathe, preen and hunt on her own.

Adults

The male eagle is smaller than the female. He weighs about 10 lbs. and the female tips the scales at about 14 lbs. Being smaller, he is slightly quicker and more agile, giving him an advantage in catching prey. She, being larger, is better able to incubate the eggs and brood the young chicks, using her body to shelter her offspring from cold, soaking rains or hot sun. The male's wingspan is a little more than 6 feet from wing tip to wing tip, the female's is between 6.5 and 7 feet.

Banding the Bird

When possible, both adults are leg banded. The female has a single silver band and was released as part of the Massachusetts Bald Eagle Restoration Project at Quabbin Reservoir in 1985. The male has a silver band on one leg and a blue band on the other. He was likely banded as a chick in a wild nest in New York state sometime around 1990. He replaced the original male, a bird released at Quabbin in 1986, when the original bird failed to return to the territory in 1995.

Chick's Growth

The chicks will be nearly full grown at 9 weeks of age. They will add some weight as they develop their flight muscles after they leave the nest. Their wingspan will be as large as or slightly larger than the adults at this time.

Fledgling facts

Once most of their wing and tail feathers are developed, the eaglets can finally leave the nest. First flights usually occur at 9 or 10 weeks of age and are preceded by vigorous exercising and flapping. When a male and female are in the same nest, the male may fledge first. The chick will typically lift off of the nest by facing into the prevailing winds and flapping. Sometimes the adults will force the eaglets to fly.

Often the first flight will be to the nearest branch above the nest. When chicks leave the nest they usually glide to a nearby tree or stump, returning to the nest tree frequently and continuing to be fed by the adults. At first the eaglets have difficulty landing on tree limbs. However, if they land on the ground, they need open space to flap their wings to become airborne.

While eaglets improve their landing and flying skills, they depend on their parents for food. The adults will bring food to where the eaglets are perched. Eaglets will stay close to the nest and nest tree during the first few weeks after fledging.

Within a month after fledging, eaglets will soar and drift over the river.

Chicks leaving the nest

The eaglets are poor hunters and may scavenge on dead prey. As the chicks develop their flight skills they harass the adults and try to take fish from them. This behavior helps eaglets to learn to forage and be independent. At 17 to 23 weeks of age, the bond between the adults and their young fades and the adults no longer tolerate harassment from their offspring. This is the time when the young eagles leave the territory, following the prevailing winds to more northerly shorelines and water bodies in search of good feeding grounds.

Migration and Distance Traveled

Most eagles don't migrate in the sense that robins and bluebirds do, preferring instead to travel only as far as they have to find food. With a strong preference for fish, this migration will typically force movement to areas of open water. Large numbers do move southward from the frozen North between November and March, so large populations of wintering eagles can be found in the western and midwestern states. This is particularly true of adult eagles with established territories. Adults will stay on their territory (up to 6 square miles) year round as long as there is open water nearby where they can hunt. Should a severe winter limit the food supply, eagles will move as far south as necessary to find open water and suitable feeding grounds.

Immature eagles wander great distances in search of food. Birds banded in Massachusetts have been sighted as far away as West Virginia and southern Canada. Eagles sighted in Massachusetts have come from as far away as Maine, New York, New Jersey, Pennsylvania, Connecticut, New Hampshire and Michigan.

Youth to Adult

The young eagle will spend the next four years of its life wandering across eastern North America looking for summering and wintering areas where food is accessible. The mortality rate for eagles during their first year of life is greater than 50%, but once they have learned to hunt and forage successfully, their chances of reaching adulthood are good. When it begins to mature at age 4, an eagle seeks a mate and establishes a territory. The territory is usually located within 250 miles of the nest where the eagle was hatched. There, the new pair of eagles will construct their own nest, but often they don't produce eggs or young during their first year as a pair. They will return in following years to raise young of their own.

Endangered Status Protection

Once threatened, bald eagles are now bouncing back following a period in which they were endangered in the lower 48 states (Alaska continues to have an abundant population; they are not found in Hawaii). Extensive use of DDT and DDE from the mid-1940s to the 1970s contributed to huge declines in population.  Since the enactment of legislation in 1972 banning their use, populations have steadily increased.

Today the majority of eagle deaths are attributed to human activities such as disturbance of nest sites, loss of habitat due to development, contamination of food sources, electrocution on electric lines, poisoning, and hunting  Non-human factors include attack of young by predators, incubation failures, illness and infection, lightning strikes, and prolonged exposure to cold, damp weather.

Protection zones around sites of eagle activity are created and maintained by federal and state wildlife authorities in cooperation with landowners. Feeding areas are closely monitored because disturbances at winter feeding areas can lead to life-threatening situations for the birds. Deliberate intrusions can result in criminal charges and substantial fines.  Protection laws include Connecticut Statutes 26-93 and three federal statutes: the Endangered Species Act of 1973, the Bald Eagle Protection Act of 1940 and the Migratory Bird Treaty Act of 1918.

References and Further Reading
Massachusetts Division of Fisheries and Wildlife, Bent, A.C.; Life Histories of North American Birds of Prey; Dover Publications; New York; Gerrard, Jon M. and Gary R. Bortolotti; The Bald Eagle: Haunts and Habits of a Wilderness Monarch; Smithsonian Institute Press; Washington; 1988. Stalmaster, M.; The Bald Eagle; Universe Books; New York, NY; 1987. Terres, J.K.; The Audubon Society Encyclopedia of North American Birds; Alfred A. Knopf, New York, NY; 1980.