The Bald Eagle, a national symbol, is known for its impressive size, but the structures it builds are equally grand. These nests, called “eyries,” are among the largest built by any bird species worldwide. They are carefully engineered to withstand harsh weather and support the weight of the birds, which continuously increases over time. The sheer scale and durability of these complex structures are a testament to the eagles’ dedication to their offspring.
Typical Dimensions and Materials
A newly constructed bald eagle nest typically averages between four and six feet in diameter. The depth of a standard active nest ranges from two to four feet, forming a massive, bowl-shaped platform. Eagles construct the foundation of their eyrie using large, sturdy sticks and branches, often broken off trees or collected from the ground. Both the male and female contribute to this construction, carrying the materials in their talons and weaving them together for strength.
The interior of the nest is meticulously lined to create a softer, insulated cup, known as the “bole,” where the eggs will be laid. This inner lining consists of finer materials such as moss, grasses, plant stalks, lichens, and sometimes even seaweed. The eagles may also use their own downy feathers for cushioning and temperature regulation.
Weight and Record-Setting Nests
The continuous annual addition of material causes bald eagle nests to accumulate immense weight over time. While a first-year nest is modest, an established, occupied nest often weighs hundreds of pounds, and many mature nests are estimated to weigh over 1,000 pounds. This weight requires the eagles to select trees with exceptionally thick and strong limbs to provide adequate support.
The largest nests ever documented demonstrate the potential of this continuous construction habit. One record-setting nest, found in St. Petersburg, Florida, was measured at 9.5 feet wide and 20 feet deep. This massive structure, examined in 1963, was estimated to weigh more than two metric tons, or over 4,400 pounds.
Nest Placement and Lifespan
Bald eagles are highly selective about where they establish their eyries, choosing locations that maximize safety and access to food. They typically select tall, sturdy trees that protrude above the surrounding forest canopy, often referred to as “super-canopy” trees. These trees provide an unobstructed flight path and offer a commanding view of the territory for spotting both prey and potential threats.
The nests are almost always located near large bodies of open water, such as coastlines, rivers, or lakes, which provide the eagles’ primary food source of fish. The longevity of these structures is remarkable, as eagles often exhibit strong “nest site fidelity,” returning to and maintaining the same nest year after year. Pairs may reuse a single nest for many decades, sometimes for as long as 35 years.