ANIMAL ESTATE client 1.01: BALD EAGLE
FOR ANIMAL ESTATES 1.0: NEW YORK, NY
SCIENTIFIC NAME : Haliaeetus leucocephalus
ANIMAL PROFILE :
RANGE: The bald eagle is native to North America and originally bred from central Alaska and northern Canada south to Baja California, central Arizona, and the Gulf of Mexico. It now has been extirpated in many southern areas of this range. Historically, bald eagles nested in forests along the shorelines of oceans, lakes or rivers throughout most of North America, often moving south in winter to areas where water remained open. Prior to the 1900s, they used as many as 80 nest sites in New York, primarily in the northern and western parts of the state. Wintering grounds are from southern Canada south, along major river systems, in intermountain regions, and in the Great Plains. New York State Dept. of Environmental Conservation
HABITAT: Bald eagles are able to live anywhere on the North American continent where there are adequate nest trees, roosts ands feeding grounds. Open water such as a lake or an ocean, however, is a necessity. Many hydroelectric plants, including some in New York, provide suitable wintering habitat for bald eagles. New York State Dept. of Environmental Conservation
HOME CONSTRUCTION: A bald eagle nest is a large structure, usually located high in a tall, live white pine tree near water. The nest is reused and added to (decorated) each year, often becoming eight or more feet deep, six feet across, and weighing hundreds of pounds. The shape of the eagle nest or aerie is determined mainly by the branch point where it's built. Sticks placed in tree forks result in cylindrical or conical shaped nests. Disk shaped nests are built on the ground or a tree branch which is nearly level. Bowl shaped nests occur where the tree trunk branches off into smaller upright branches. Bald eagles build their nests in large trees near rivers or coasts. A typical nest is around 5 feet in diameter. Eagles often use the same nest year after year. Over the years, some nests become enormous, as much as 9 feet in diameter, weighing two tons. Even when a nest tree falls or a strong wind blows a nest down, the established pair usually rebuilds at or near the site within a few weeks if it is near the breeding season. The nest may be built in a tree, on a cliff, or even on the ground if there are no other options available. Eagles are territorial during nesting season. They will keep other eagles out of their own nesting area. Their nesting territory is usually one to two square miles. from Bald Eagle Info. link
BUILDING MATERIALS : A mated pair adds on to their nest each breeding year. The nests are primarily built of sticks and can eventually weigh up to two tons. Bald Eagle nests are among some of the largest nests in the world.
BUILDING MOTIVATION : Females lay a clutch of one to three eggs, but usually two. Incubation lasts from five to six weeks. One problem that greatly hampers the recovery of the species is sibling competition. A female lays her eggs a few days apart, and incubation begins with the first egg. One to two days is the normal age difference between eaglets. Older hatchlings are able to dominate the youngers ones for food because of their size. In a three-egg brood, the third chick has little chance of survival. Nest duties among the pair are shared equally; both the male and the female will hunt and offer food to the eaglets.
THREATS: Over the years, the Bald Eagle population has suffered from excessive hunting and pollution. In the early part of the century, hunting eagles was a popular sport. Eagles were shot not only for their feathers, but also because they posed a "threat" to livestock (e.g. sheep) and hampered the fishing industry. In recent years, however, pollution has greatly contributed to the demise of the species. As a result of both land and water pollution, a significant amount of the Bald Eagle food supply has been killed. In particular, the use of pesticides such as DDT had been the greatest threat to the species. Pesticides are often found in fish, the major food supply for eagles. DDT in a female's body disturbs the shell-making process, causing her to produce very weak shells or no shells at all.
INTERESTING FACTS : Much to Benjamin Franklin's dismay, the Bald eagle was adopted as the national emblem in 1782. He said that the Bald Eagle was a bird of bad moral character (stealing food) and recommended the turkey instead. None the less, the bird serves as a symbol of wilderness and freedom. Bald eagles are only partially migratory; if they possess access to open water, they will remain at that nesting sight year round. Those that do not have access to water leave the frozen countryside in the winter and migrate to south or to the coast.
REFERENCES:
Harris, M. 2002. "Haliaeetus leucocephalus" (On-line), Animal Diversity Web. Accessed October 30, 2007 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Haliaeetus_leucocephalus.html .
Gerrard, Jon, M.. et. al., The Bald Eagle: Haunts and Habits of a Wilderness Monarch. Smithsonian Institution Press,1984.
Mackenzie, John, P.S.. Birds of Prey. Paper Birch Press Inc., 1986.
Porteous, Peter, L.. National Geographic: Eagles on the Rise. 182(5), November 1992.
Savage, Candace. Eagles of North America. NorthWord Inc., 1987.