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Breeding Cycles of Bald Eagles

 – Mating and Nesting

Monogamous, they mate for life until the death of one mate. Eyries, large nests lined with twigs, soft mosses, grasses, and feathers, about 2 feet deep and 5 feet wide that they build at the top of sturdy trees grow larger (about 10 feet wide and several tons) when they add new nesting materials each year while repairing before breeding. Nest shapes are determined by whether or not sticks are placed in deep, vertical forks (conical nests), ground or level branches (disk-shaped nests), or tree trunks that suddenly branch into smaller upright branches (bowl-shaped nests). They usually nest in trees, but sometimes on cliffs, and often within 100 miles of where they hatched, staying in the same neighborhood as their parents. Territorial while nesting, they will attack other eagles within their area. The nesting cycle lasts about 20 weeks.

Bald eagles are sexually mature around four or five years old and dedicate themselves to finding a mate to raise offspring with. Mating season varies by region. Eagles do not copulate in the air like some believe because pairs have been seen whirling through the air with talons locked in a form of courtship or ritualized battle. Breeding may not occur annually for some eagles by voluntary choice. They may instinctively realize bad timing because of weather, nesting site availability, or food.

In the springtime, five to ten days after copulation, the female lays 1 to 3 speckled off-white or buff colored goose-sized eggs a few days apart. During incubation, male bald eagles bring green sprigs of conifer branches to the nest, possibly for deodorizing or shade. Both parents share the duties: hunting, egg incubation, nest watch, eaglet feeding, and eaglet brooding; however, the female does most of the nesting. One parent is always on the nest to keep eggs warm and safe from squirrels, ravens, and gulls. The male will often eat the head of fish and bring the remains to the nest. He shares brooding duties so that the female can stretch, defecate, bathe, preen, and hunt on her own. Eagles need privacy and quiet to breed. If they are disturbed, they may abandon their nest. People should use binoculars and spotting scopes for viewing at a distance.

Eaglets hatch after an incubation period of about 35-38 days in the order they were laid, by using their egg tooth, a pointed bump on the top of the beak, to break the shell. Hatching can take half a day to two days. Newly hatched chicks measure 4 to 5”, with soft, grayish-white bodies, wobbly legs, and partially closed eyes. When two chicks survive, the older one may kill the smaller one and the parents will not stop them. Parents feed them by shredding pieces of meat with their beaks and while moving around in the nest they wall with their talons balled into fists to avoid harming their young. Eaglets’ diets consist of fish with supplements of water fowl or birds.

Eaglets grow a pound every four or five days and can hold their heads up for feeding around two weeks. At three weeks, they are one foot high and their feet and beaks are near adult size. At six weeks, they are about the size of their parents. They are full size at about 12 weeks and learn to fly. When their wing and tail feathers are fully developed, they can leave the nest. Before first flights, which may be to the nearest branch above the nest, eaglets do vigorous exercise and flapping. They will lift off by facing into prevailing winds and flapping or may be forced to fly by parents.

About 40% survive their first flight and only about half survive their first year for various reasons including starvation and the inability to recognize poisoned food. 

History of Bald Eagles

What Do Bald Eagles Look Like? – Physical Descriptions

Where Do Bald Eagles Live?

What Do Bald Eagles Eat? – Food Sources and Hunting Habits

Breeding Cycles of Bald Eagles – Mating and Nesting

Migration Patterns of Bald Eagles

Normal Lifespans and Causes of Death for Bald Eagles

Patriotic Poetry – The Eagle as National Emblem