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The bald eagle builds the largest nest of any North American bird, up to 13 feet deep, 8.2 feet wide, and 1.1 tons in weight.
- A typical nesting landscape would be forested and include rivers or lakes that offer areas of shallow water. These landscapes provide for basic needs: water to drink, fish to eat, forest trees for shelter and a place to raise young, and perches for hunting and resting.
- Together, the male and female bring new sticks to strengthen the structure, and also grass-like material to form a soft cup in the center of the nest where the eggs will rest.
- Some pairs need to rebuild their nest almost from scratch if winds and bad weather have damaged it. This nesting activity starts one to three months before the female lays eggs.
- Bald eagle's large nest is called an aerie. A typical nest will range from 1.8 to 3 meters (6-10 feet) in diameter and about 1.8 to 3 meters (6 to 10 feet) high. The nest cavity, where the eggs are laid, will be about 30 to 40 centimeters (12 to 16 inches) in diameter and about 10 centimeters (4 inches) deep.
- First year nests are usually smaller, and the nest size will increase each year as eagles re-use the nest and add sticks to it.
- Bald eagles are very territorial birds, and most breeding pairs return to the same nest site year after year. They may use the same nest annually for as many as 35 years, or they may build additional nests in their nesting territory, and alternate the use of them from year to year.
- Bald eagles generally nest near coastlines, rivers, and large lakes where there is an adequate food supply.
- In areas where trees are few and far between eagles will nest on the ground or on the tops of cliffs!
- Ground nests are built of whatever's available, such as kelp and driftwood near coastal shorelines.
- They nest in mature or old-growth trees, snags (dead trees), cliffs, and rock promontories. In forested areas, bald eagles often select the tallest trees with limbs strong enough to support a nest that can weigh more than 1,000 pounds.
- Nest sites typically include at least one perch with a clear view of the water, where they forage.
- Eagle nests are constructed with large sticks, and may be lined with moss, grass, plant stalks, lichens, seaweed, or sod.
- Bald eagles pick up broken sticks from the ground, and sometimes break branches off trees. They naturally take as many sticks as they can find close to the nest, but may lug some branches as far as a mile, carrying them in their talons.
- They usually start building in the top quarter of the tree, below the crown, near the trunk, where branches are thick and strong enough to support the heavy nest. They interweave the sticks, and fill in spaces with grasses, mosses, cornstalks, Spanish moss, and other fibers.
- Throughout the season, and sometimes even during fall and winter, eagles keep adding sticks to the nest, and they reuse nests, continuing to build on to them, for many years. The average eagle nest is only 1.5-1.8 meters in diameter and 0.7-1.2 meters tall.
- Both sexes bring materials to the nest, but the female does most of the placement. They weave together sticks and fill in the cracks with softer material such as grass, moss, or cornstalks.
- Eagles tend to nest in tall, sturdy conifers that stick up above the forest canopy, providing easy flight access and good visibility.
- Nesting behavior starts with some clearing out any unwanted debris, fixing any damaged areas of the nest, and adding on. The early season work is usually sporadic and not terribly serious.
- Some non-migratory pairs may stay in the vicinity of their territory all winter and can be seen working on their nest sporadically all year long.
- The renovation behavior makes the nest ready to house the next generation of eagle young and is part of the courtship process as it strengthens the bond between mates.
- Eagles need some degree of insulation and isolation from human activity, though sensitivity to disturbance seems to vary widely.
- The nest itself needs to be higher than the surrounding vegetation to provide both easy access and a clear view of possible threats to the nest.
- The trees that are tall and strong enough to satisfy eagle nesting needs tend to be old and sometimes may be nearing the end of their life. Occasionally, the nest tree dies but stays strong for a time and the eagles will continue to use their nest, despite the death of the nest tree, often until the tree or nest falls down.
- Pairs building a completely new nest often dedicate much of their springtime activities to carrying nesting material and working on the new nest.
- The 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.
- Tree shape, size, and location are more important to an eagle looking to build a new nest than is the tree species, but some of the trees more likely to meet nesting needs are pines, spruces, firs, oaks, hickories, and cottonwoods.
- Bald eagles usually like to have a clear view in all directions around their nests.
- Nest trees tend to be the tallest in the surrounding area, called super-canopy trees. Nests tend to be very large and rather heavy, so the best nest trees are tall, strong healthy trees.
- Pairs that are building a new nest usually choose a living tree as the base for their nest though there are often some dead trees, called snags, nearby that serve as lookout posts.
- Some eagle pairs build an alternate nest (usually within a mile from first nest) within the eagle territory, and the pair may take turns nesting between these from year-to-year.
- When an eagle nest blows down, the eagle pair will usually build another nest nearby.
- Because some eagle nests are so large, it is not unusual to be able to spot these nests with a naked eye from a mile away.
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