Florida Bald Eagle Nesting Behavior
Bald eagles, which pair for life, usually begin returning to their nests in late September or early October. This is the time to begin looking for the dramatic aerial displays of courtship, when the birds snare each other's feet in mid-flight and, with their wings and feet outstretched, tumble close to the ground, parting only just before striking the earth.
Early nesters may begin laying eggs in November, while late nesters may wait until mid-January. A tall pine tree is the favored habitat for Central and North Florida eagles. The nests are commonly as much as 80 to 100 feet high, just below the top of the tree. Eagles in South Florida often use mangrove trees for their nests; situated only 20 feet off the ground, these nests are often the easiest to see.
A bald eagle nest, like the birds themselves, are an impressive size. It is the largest nest of any bird in North America, and the same nest is constantly added to year after year. It may eventually weigh as much as two tons. The largest ever recorded in Florida was 10 feet wide and 20 feet deep.
Eagles will use sticks as long as six feet to weave the frame of a nest together. Smaller sticks are added and intermixed with the large ones. Weeds and grass, sometimes with dirt still attached, are placed at the bottom.
Nests are shaped according to the tree. Cylindrical nests are formed when a tree's branches grow upright. Broader, cup-shaped nests are made where the branches are more spread out. From scratch, a nest takes only about four days to build. Eagles sometimes have more than a single nest in an area, though they will use only one during a breeding season.
Females lay two or three eggs, several days apart. The eggs are twice the size of the average chicken egg. Both parents take turns during the incubation period, which lasts about 32 days. The eggs are turned about once an hour so they will warm evenly. To transfer body heat, both parents develop a brood patch in their lower breast where the feathers are absent and the blood vessels close to the surface.
The chicks emerge several days apart. It takes a chick about 24 hours to break out of its shell, using an egg tooth, a sharp point at the top of its bill which is abraded off after about a month. This is survival of the fittest from the start: the parents never help a chick break out of its egg.
When food is scarce, the parents do not prevent the older and larger chick from taking most of the food, even if it means killing off its siblings. The parents never regurgitate food for their young. Instead, the chicks devour bites of food torn off for them by their parents.
A newly hatched chick weighs about three ounces and bears a thick coat of gray down. It is able to fly at about eight weeks. It will leave the nest at about 10 to 12 weeks, but may remain in a tree near the nest for another four to six weeks so it can still be fed by its parents. Then, beginning around April, the eaglets will fly north, going perhaps as far as Canada, a distance of over 2,000 miles.
An estimated one-half of Florida's eaglets do not survive beyond their third year. A mature eagle in the wild may live 25 to 35 years; in captivity, as long as 50 years.
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