Nest sites are generally in a forested area and not far from a major water body. In essence, while nests may be within a broadly forested zone, they are located close to the edge of larger openings created by lakes, rivers or seacoasts, grasslands and so forth. Most, if not all nests are within one mile (1.6 kilometers) of a major water body and the highest percentage are within 600 feet (186 meters) of water. Nests are primarily in trees with coniferous, preferred but large, flat-limbed deciduous trees are used. The tree species vary geographically and include Douglas-fir, ponderosa pine, red pine, loblolly pine, sycamore, elm, cypress, mangrove, and black cottonwood. The selected tree is usually taller and generally larger than the surrounding trees or is more isolated than the others. A clear flight approach from the water side is preferred and perch trees or elevated lookouts are located nearby. The stands are generally mature or old-growth with second growth shunned by nesting eagles. The nest may be built at almost any height from the ground up to 80 feet (24.8 meters) but most nests are in excess of 30 feet (9.3 meters) and the average may be closer to 50 feet (15.5 meters). In treeless areas, nests are built on the ground, on hillsides, ridge tops or sea stacks on offshore islands. Manmade structures are used.
Nests are constructed of branches, sticks and debris of various kinds. Recently-constructed nests that have not been refurbished vary in height from one to three feet (0.3 to 0.9 meters) and from three to six feet (0.9 to 1.9 meters) in diameter. Over the years, the nests are repaired and added to such that the largest may reach 20 feet (6.2 meters) in height and over 9 feet (2.8 meters) in diameter, weighing some 4,000 pounds (1,814 kilograms). Most probably last only about five years but some have been refurbished and used for 35 years. One nest tree was used for over 70 years in Alaska. The interior cavity used to receive the eggs is a depression about 4 inches (10.2 centimeters) deep and 14 inches (35.6 centimeters) in diameter. The lining is comprised of finer items such as grasses, sedges, seaweeds, Spanish moss or other plant materials. Leafy twigs are added during the nesting period. Up to five extra nests may be built within one mile (1.6 kilometers) of the main nest with some as close as 0.25 of a mile (0.4 kilometers) away. Both sexes bring nesting material but the female does most of the construction.
Bald eagles are single-brooded with two being the typical clutch size, although if not two, it is more likely to be three than one. The eggs average 2.8 inches long (71.1 millimeters) by 2.1 inches (53.3 millimeters) wide but may be as large as 3.3 by 2.5 inches (83.8 by 63.5 millimeters) or as small as 2.3 by 1.9 inches (58.4 by 48.3 millimeters). They are rough-shelled, white and non-glossy. If the first clutch is lost early enough, a second may be laid after four weeks or more but captive birds may replace eggs earlier. The number of replacement eggs may not equal the number lost. Egg laying starts as early as October 26 in Florida with the normal laying period becoming progressively later as you move westward and north such that in parts of Alaska, May is the normal end of the laying period. Between late October and mid-May, egg laying occurs in virtually every month somewhere in North America.
The interval between egg laying can be as much a four days with an incubation period of 34 to 36 days. Both sexes incubate with the female probably doing most of the day time incubation. The nestling period is 10 to 12 weeks with constant attention by at least one parent during the first two weeks. Brooding the young at night lasts for at least four weeks after which the young are quite mobile and they move from the nest cup to the outer portions of the nest. Siblicide is documented but is apparently less common than in the Golden Eagle. The killed young is often eaten. The family bond during the early flight stage is of variable duration and ends between six and 13 weeks after fledging. Following dispersal, birds may return to the general area of their birth during their second or third calendar year. In declining populations, the fledging rate may be as low as 0.34 young per nest whereas stable populations fledge at least 0.75 young per nest. A high of 1.03 fledged young per nest was noted in populations that were increasing. Widespread studies and summaries show that about 43 percent of territorial pairs produce young and that about 58 percent of occupied nests were successful.
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