The bald eagle, America's National Bird, is the only eagle unique to North America. Bald eagles are found over most of North America, from Alaska and Canada to northern Mexico. About half of the world's 70,000 bald eagles live in Alaska. Combined with British Columbia's population of about 20,000, the northwest coast of North America is by far their greatest stronghold for bald eagles. There are two recognized subspecies of Bald Eagle. The southern bald eagle, Haliaeetus leucocephalus leucocephalus, is found in the Gulf States from Texas and Baja California across to South Carolina and Florida, south of 40 degrees north latitude. The northern bald eagle, Haliaeetus leucocephalus alascanus, is found north of 40 degrees north latitude across the entire continent. The largest numbers of northern bald eagles are in the Northwest, especially in Alaska. The northern bald eagle is slightly larger than the southern bald eagle.
The Bald Eagle is a powerful flier, and soars on thermal convection currents. It reaches speeds of 35–44 miles per hour when gliding and flapping, and about 30 miles per hour while carrying fish. Bald Eagles normally squeak and have a shrill cry, punctuated by grunts. They do not make the scream that is found in films; this is usually the call of a Red-tailed Hawk, dubbed into films for dramatic effect.
The Bald Eagle prefers habitats near seacoasts, rivers, large lakes, and other large bodies of open water with an abundance of fish. Studies have shown a preference for bodies of water with a circumference greater than 7 miles, and lakes with an area greater than 3.8 square miles are optimal for breeding bald eagles.
Bald Eagles are sexually mature at four or five years of age. When they are old enough to breed, they often return to the area where they were born. It is thought that Bald Eagles mate for life. However, if one member of a pair dies or disappears, the other will choose a new mate. A pair which has repeatedly failed in breeding attempts may split and look for new mates. Bald Eagle courtship involves elaborate calls and flight displays. The flight includes swoops, chases, and cartwheels, in which they fly high, lock talons, and free fall, separating just before hitting the ground.
The plumage of an adult Bald Eagle is evenly brown with a white head and tail. The tail is moderately long and slightly wedge-shaped. The beak, feet, and irises are bright yellow. Immature Bald Eagles are distinguishable from the Golden Eagle in that the former has a more protruding head with a larger bill, straighter edged wings. Body length ranges from 28–38 inches.
The average lifespan of Bald Eagles in the wild is around 20 years, with the oldest living to be about 30. In captivity, they often live somewhat longer. In one instance, a captive individual in New York lived for nearly 50 years. As with size, the average lifespan of an eagle population appears to be influenced by its location.
The Bald Eagle is extremely sensitive to human activity, and occurs most commonly in areas free of human disturbance. It chooses sites more than 0.75 miles from low-density human disturbance and more than 1.2 miles from medium- to high-density human disturbance.
The Bald Eagle's diet is opportunistic and varied, but most feed mainly on fish. To hunt fish, easily their most important live prey, the eagle swoops down over the water and snatches the fish out of the water with its talons. They eat by holding the fish in one claw and tearing the flesh with the other. Eagles have structures on their toes called spiricules that allow them to grasp fish. Osprey also have this adaptation. Bald Eagles have powerful talons. Sometimes, if the fish is too heavy to lift, the eagle will be dragged into the water. It may swim to safety, but some eagles drown or succumb to hypothermia. When competing for food, eagles will usually dominate other fish-eaters and scavengers, aggressively displacing mammals such as coyotes and foxes, and birds such as corvids, gulls, vultures and other raptors. Bald Eagles may be displaced by or themselves displace Golden Eagles, with neither species known to be dominant. Occasionally, Bald Eagles will steal fish away from smaller raptors, such as Ospreys, a practice known as kleptoparasitism.
Permits are required to keep Bald Eagles in captivity in the United States. Permits are primarily issued to public educational institutions, and the eagles which they show are permanently injured individuals which cannot be released to the wild. The facilities where eagles are kept must be equipped with adequate caging and facilities, as well as workers experienced in the handling and care of eagles. Bald Eagles cannot legally be kept for falconry in the United States. On June 2007 the Interior Department of US took the American bald eagle off the Endangered Species List. The bald eagle will still be protected by the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act. The Bald Eagle Protection Act prohibits the take, transport, sale, barter, trade, import and export, and possession of eagles, making it illegal for anyone to collect eagles and eagle parts, nests, or eggs without a permit. Native Americans are able to possess these emblems which are traditional in their culture.