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Eagles' Nest Sizes

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Eagles are amazing birds for several reasons, and the size of their nests is just one. Another is their surprising and wondrous courtship -- an incredible ritual to witness. Once a mating pair is established, the business of building a nest begins in earnest.

The Courtship Ritual

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Scientists once believed the Earth was flat; there's only one galaxy; and eagles mate for life. They also believed the ritual where eagles soar high into the sky, clutch each other's talons and whirl end-over-end to the ground was their way of copulating. But now, biologists believe that while that may be one purpose of the ritual, they also may be defending territory or engaging in communion to establish a courtship. Once a mating pair has become established, they begin to search for a suitable site on which to build their magnificent nests. Eagles are monogamous, but if one dies, or if the relationship produces no young, one or the other eagle may go off in search of another mate.

The Building Site

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The mating pair will search for a suitable location on which to build their nest. They look for large trees, but if there are no trees available, they will settle for a cliff or the ground. Once they choose their site, they defend it fiercely from other eagles. They both participate in seeking out building materials such as twigs, sticks, moss and leaves. They build near rivers or lakes so they can fish, but deciding on site can be challenging because eagles tend to return to their place of birth to begin their own families. Since a mating pair may consist of eagles from two completely different areas, both the male and female have to agree on the location.

The Nest Construction

The size of an eagles' nest, also called an "aerie," increases from year to year. Eagles usually return to the same nest annually. The shape of the nest is determined by its placement and how the nest will fit into the construction site. It can be cone-shaped, circular, bowl-shaped or a somewhat flat platform with an indentation 2 to 3 feet deep. This part of the nest, where the eggs will be laid, is called the "bole" and is lined with softer materials and eagle down feathers. The nest is constantly being upgraded and rearranged according to available components. The nest grows larger and heavier during the nesting season and as the years pass.

Eagle Species

There are more than 60 species of eagle, but only two live in North America, and they are the largest: the bald eagle and golden eagle. An average nest is about 5 to 6 feet and can grow as large as 12 feet in diameter and weigh in at more than 2 tons. The size of the nest increases with the size of the bird, with the bald eagle and the golden eagle building the biggest nests among eagles.

Legend Has It

Since the bald eagle was once threatened with extinction, it was placed under the protection of the U.S. government in 1940. The use of a pesticide called DDT was used extensively for about 30 years until it was discovered to interfere with eagle reproduction. Eagles were further protected under the Endangered Species Act, but their numbers have increased substantially. However, since they were being watched so closely, their nests have been under observation and some were found to be inconceivably large. A breeding pair in Ohio used the same nest for 34 years, and it grew to an incredible 12 feet tall and 9 feet around. Another nest, found in St. Petersburg, Fla., had a diameter of 9.5 feet and height of 20 feet. As of 2012, eagles' nest all over the United States are the subject of live camera feeds, and America's fascination with these birds and their nests has never been keener.