Hawks and eagles are carnivores whose hooked beaks and curved claws are adapted for prey capture.
Modern eagles are divided into four groups: snake eagles, buzzard-like eagles, booted eagles, and fish eagles. Snake eagles inhabit Europe and Africa and feed primarily on reptiles and amphibians. Buzzard-like eagles include the largest and most powerful eagles of the world such as the harpy and the Phillipenes monkey eating eagle. There are thirty species of booted eagle which vary from almost the size of the harpy to a mere half pound. Golden eagles are booted eagles. Sea and fish eagles, a group which includes the bald eagle, are primarily found in aquatic environments. The species which varies in its diet is the African vulturine fish-eagle which feeds largely on palm fruit. The white-tailed sea eagle is the closest relatives of bald eagles (Tucker, 1994).
The large eyes of eagles leave little room for eye muscles so the necks of bald eagles can move over 270 degrees. Eagle eyes contain photoreceptors at five times the density found in human eyes. Each eye possesses three concentrated regions of photoreceptors (called foveas) and, like other birds, possess 5 types of cones (Tucker, 1994).
Bald eagles primarily feed on fish which are either swimming close to the surface or which are dead. They consume 6-11% of their body weight per day. Their highly acidic stomach dissolves fish bones. A mature eagle’s crop can store two pounds of food, allowing eagles to survive times of food shortage (they may last a month without food). Bald eagles may steal food from other birds, such as ospreys (Tucker, 1994).
Courtship in bald eagles involves mutual preening and pecking. They usually mate for life as long as their breeding is productive (Tucker, 1994).
Although bald eagles usually nest in trees, they have been observed to nest on large cacti and on the ground on treeless islands. Eagles typically reuse their nests and as they become larger they may eventually break the branches which support them. One eagle nest was used over 60 years and reached a size of 18 square feet. Another nest weighed two tons and measured 10 feet high, 8 feet across. Another nest measured 20 feet high and 10 feet across (Tucker, 1994).
A typically nest contains 1-3 eggs; usually two. One of the two parents stays with the nestlings about 98% of the time. By 10 to 12 weeks of age, the young eagles begin to leave the nest (Tucker, 1994). Eagles weigh 1-2 pounds at birth. Within three weeks, they gain weight at a rate of 4 ounces per day. At 2 months, eagle chicks have reached 90% of their adult weight and female chicks may even be larger than their father. A full grown eagle can consume two pounds of food in one meal (Gerrard, 1988).
When North America was colonized, bald eagles nested in every state in the U.S. other than Hawaii (Gerrard, 1988). In 1885, the state of Pennsylvania offered 50 cents for birds of prey (including eagles) as an attempt to limit predation on chickens. In 1917, the state of Alaska offered 50 cent bounties on eagles, a price which increased to $2 by 1949. By that time, more than 100,000 bald eagles had been killed. Bald eagle eggs often sold for $5 in the early 1900s and it is thought that about half of the eagle eggs laid in Florida were taken for sale. In 1940, the Bald Eagle Act protected bald eagles and in 1952, this act was extended to the territory of Alaska. In 1962, golden eagles were also protected under this law. The current penalty for killing a bald eagle can be $5,000 and one year in jail for the first offense and $20,000 and 2 years in prison for the second offense (Tucker, 1994).
In 1951, more than 106 million pounds of DDT were used in the United States. By 1974 (one year after the Endangered Species Act was passed), there were only about three thousand eagles in the continental 48 states which included only 721 breeding pairs. In the 1970s, bald eagles had disappeared from many areas of their former territory, including much of the north-central U.S. The number of eagles had increased to 8-12,000 by the mid-1990s. As part of the Endangered Species Act, 55 million acres of habitat had been protected. DDT was banned in 1972 and in 1991, lead shot was banned (Tucker, 1994).New York was the first state to begin to reintroduce bald eagles into the wild in 1976 and almost 200 eagles had been released by 1989. By the mid-1990s, many felt that bald eagles should be listed on the Endangered Species List as "threatened" rather than "endangered" because of the success of these conservation efforts (Weidensaul, 1996).
|The following are photos of immature bald eagles.|