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DESCRIPTION
The adult bald eagle is a striking dark brownish black bird with a white head and tail. Juvenile birds are a mottled brown with white blotches. They do not obtain the full distinctive plumage of the adults until they are four or five years old. Bills, legs, and feet are a deep yellow.
SIZE
Second in size only to California condors (Gymnogyps californianus) and about the same size as golden eagles (Aquila chrysaetos), bald eagles dwarf most other North American raptors. Their wingspans range from six and a half to seven and a half feet, while body length varies from about three to three and a half feet. Bald eagles weigh from six to eight pounds. Females are larger than males and have a slightly longer wingspan.
LIFE SPAN
Bald eagles have lived up to 48 years in zoos, although their life span in the wild is likely far shorter.
DISTRIBUTION AND HABITAT
Bald eagles occur from Baja California and Florida north to Newfoundland and Alaska. Within this area, they are nearly always found near water, along rivers, lakes, or the sea coast and coastal marshes, reservoirs, and large lakes. They also pass over mountains and plains during migration. The northern and interior populations may migrate to open water in the winter months.
Bald eagles breed in much of Alaska (where they are most common), Canada, the Pacific Northwest, along the East Coast, the Mississippi River, and the Gulf Coast, around the Great Lakes, and in other areas with sufficient water and wildlife. The birds winter along the coasts and across much of the U.S. Some reach northwestern Mexico.
Near Washington, D.C., bald eagles have increased around the Chesapeake Bay and its tributaries. They nest at several sites around the Capital Beltway, and have been seen flapping over the National Zoo.
Although unique to North America, the bald eagle's closest relatives live in other parts of the world. These include the African fish-eagle (Haliaeetus vocifer) of sub-Saharan Africa and the white-tailed sea-eagle (Haliaeetus albicilla) of Eurasia.
DIET
Bald eagles are predators. They have several adaptations that fit them for that role. They have excellent eyesight and the frontal setting of their eyes gives them excellent binocular vision as well as peripheral vision.
The eagle has a strong, hooked beak with which it tears food, but it uses its powerful, taloned feet to capture prey. Bald eagles prefer fish, which they often capture by swooping down and snatching them from the water's surface. Another successful technique is to wade in the shallow water catching fish with the bill. They also take birds, especially waterfowl, and occasional mammals.
In addition to eating other animals such as ducks, muskrats, and sometimes turtles, they eat carrion willingly, and are notorious for robbing osprey of their catches. Eagles will wait on a favorite perch for an osprey to return to its nest with a fish in its talons for its own young, then harasses the smaller raptor until it is forced to drop its prey for the eagle to retrieve.
BEHAVIOR
Bald eagles spend hours perched in trees overlooking water, their keen eyes alert for feeding opportunities. When not fishing, they sometimes steal food from ospreys, pursue injured or healthy waterfowl, or settle in for a meal of roadkill or fish chopped up in turbines at dams (including Maryland's Conowingo Dam).
REPRODUCTION
Southern bald eagles remain on or near their breeding territory throughout the year and probably mate for life. More northern birds may migrate long distances over the winter months and it is unknown whether pairs remain together during migration. Initiation of courtship depends on the latitude. Southern birds may begin courtship and nesting activity in the late fall or early winter, while it is more common for northern birds to court and nest in the early spring. Copulation occurs on branches or other secure perches and is preceded by tail pumping and wing flapping displays by the male.
Eagles construct their nests near water in tall trees or on cliffs using large sticks. The nest is lined with twigs, grasses and other soft materials. Each year, a pair works together to build a large stick nest high in a tree or on a cliff.
Sometimes a pair reuses the same nest for years (such as a pair that nests at Great Falls, Maryland). In Florida, bald eagles nest almost year round; they begin nesting from March to May in other areas. Since these nests are used year after year, they may become very large.
Bald eagles lay two, occasionally three, eggs that are incubated by both parents, in turns for 34 to 36 days. Often only one chick survives, but if food is plentiful they may rear two or occasionally three. Young birds fledge after 12 weeks and remain with the parents for another month.
CONSERVATION
When the bald eagle was adopted as our national symbol in 1782, there were between 25,000 and 75,000 birds nesting in the lower 48 states. Illegal shooting, habitat destruction, lead poisoning, and the catastrophic effects of DDT contamination in their prey base reduced eagle numbers to a mere 417 pairs by 1963. Legal protection began with the Bald Eagle Protection Act of 1940 and continued with the Endangered Species Preservation Act of 1966 and the 1978 listing under the Endangered Species Act of 1973. The single-most important regulation affecting bald eagle recovery may have been the banning of DDT for most uses in the United States in 1972.
In 1995 the U.S. Fish and Wildlife Service down-listed bald eagles from endangered to threatened in most of the United States. They were never listed in Alaska, and had been already been listed as threatened in Michigan, Minnesota, Wisconsin, Oregon, and Washington. In the 17 years since they were declared endangered in most of the country, bald eagles have undergone a strong increase in numbers and an expansion in range. Private organizations, state, and federal agencies counted 4,450 occupied nesting territories, a ten-fold increase from the 1963 low.
Though the recovery has been spectacular, bald eagles remain threatened by illegal shooting and loss of habitat due to wetland drainage and human occupation of waterfront areas. Lead poisoning from shot ingested when feeding on carrion was a major problem prior to the phasing out of lead shot for waterfowl hunting in 1991. Large quantities of lead remain in the environment. Over the winter of 1994-95, 29 bald eagles died in Arkansas and nine died in Wisconsin from an unknown toxic agent. In the past 15 years the National Wildlife Health Research Center has diagnosed more than 100 cases of poisoning in bald eagles. Many of these cases are believed to be intentional poisonings through illegal use of pesticides and other restricted chemicals such as strychnine. DDT breakdown residues remain in the environment and continue to cause reproductive problems for eagles in many parts of the country.