Bald eagles feed primarily on fish, although small mammals, birds, and carrion can make up a substantial part of their diet. Eagles are opportunistic feeders, often relying on crows, ravens, and vultures to lead them to carcasses or injured prey. Nests are built of sticks and twigs with an interior lining of moss or grass. Broods usually consist of two to three eggs, and both the male and female eagle incubate the eggs for a period of 21 to 46 days. The nestlings are quite helpless, relying on both parents for food and protection for most of the 10 to 13 weeks that they are in the nest.
Eagles begin their southward migration as the ice begins to appear in the fall.
They choose locations with open water and ample food for their winter home. Often conditions are difficult in the winter as many birds converge on an area with a limited food supply. At the first sign of moderating weather, the birds begin their northern migration, often returning to the nest they used the previous year. They repair and improve the nest by adding sticks and vegetation. Because they are always being refurbished, eagle nests can become very large.