Unlike fall migration that is directed by food shortages, the spring movement is believed to be mostly driven by photoperiod, or day length. Increasing amounts of daylight is believed to be the primary cue for eagles to move north. Within this framework, other factors are known to influence eagle movements once they decide to move.
In southern British Columbia the nest building begins seriously in January. If the nest is lost a new nest may be started earlier. The cycle begins afresh.
Both male and female work together to construct a nest of sticks lined with finer materials, usually high in a living tree. They add new material to the nest each year.
Both sexes participate in nest building, which usually begins 1-3 months before egg-laying. Generally built in one of the largest live trees available with accessible limbs capable of supporting the nest. Nests built in top quarter of tree just below the crown, against the trunk or in the fork of large branches close to the trunk. Nest constructed from sticks collected on the ground or broken off of trees. Grasses, mosses, and other material may be added as filler. The nest bole is lined with finer woody material and ultimately with downy feathers from adults. Additional materials added throughout the year, including daily additions during breeding season. Nests used for multiple years may reach enormous dimensions. Bald eagle nests are among the largest nests of all birds; Typical size is 5-6 feet in diameter and 3 feet tall! Famous Ohio nest used for 34 years measured almost 9 feet in diameter, close to 12 feet tall, and weighed over 2 tons! Record St. Petersburg, Florida nest was 9.5 feet in diameter and 20 feet tall!
Caption Page: Range
The bald eagle's natural range covers most of North America, including most of Canada, all of the continental United States, and northern Mexico. It is the only sea eagle endemic to North America. Occupying varied habitats from the bayous of Louisiana to the Sonoran Desert and the eastern deciduous forests of Quebec and New England, northern birds are migratory, while southern birds are resident, remaining on their breeding territory all year. At minimum population, in the 1950s, it was largely restricted to Alaska, the Aleutian Islands, northern and eastern Canada, and Florida. Today, they are much more common (almost attaining their peak numbers pre-colonization in North America), and nest in every continental state and province in the United States and Canada.
Facts and Photos