Anatomy of a Bald Eagle Nest

2015 nesting season:  The female bald eagle laid two eggs this season, on 2/16-17 /15 and 2/20/15. Incubation takes approx. 5 weeks. Bald eagle nests are, by most accounts,  the largest bird nests in the world. 

On Sunday morning, the Duke Farms female brought new nesting material into the nest. Always remodeling. The adult eagles build their massive nests -- which weigh hundreds and hundreds of pounds -- solely with beak and claw. Although a pair of eagles can build a nest in less than a month, the nest itself seems to be forever a work in progress, with modifications and materials added over the years. The nest work continues after the eggs are laid - when eaglets are in the nest, and after nesting season. The host tree can be anything from a cottonwood to a sycamore, so long as sturdy enough to support a thousand-pound nest. And the nest must be big enough not only for two adults but for nestlings that grow as large as their parents and need a lot of room. By then, the raptors are roughly three feet long from head to tail, and their wingspans are six feet or more. They take up a lot of space. The nests need to be very sturdy as well, because when the eaglets learn to fly, they jump up and down, flapping their wings.

The eagles build the nest about two-thirds of the way up the tree, where stout branches become the girders that support the structure. 

In this late January shot of the Duke Farms nest, the bowl is covered with snow. First comes the outer framework, made of large sticks. The eagles often get the sticks by landing forcefully on the limbs of dead trees and snapping the branches off, then carrying them in their talons back to the nest. These fresh from the tree sticks tend to last longer than sticks taken from the ground. The middle layer is called the bowl. This liner is made up of such pliable materials as marsh grass, field grasses, corn husks and pine straw. The top layer is the egg cup, made of soft plant material with excellent insulating qualities that help keep the eggs warm when the parents take a break. Sometimes the eagle will bring in some evergreen twigs as well. "Some scientists believe this is done for a variety of reasons, including camouflage, insect repellent, or to signal to other eagles that the nest is occupied," says Thom Almendinger, Duke Farms Director of Natural Resources. Bald eagles typically make their nests near water, which makes sense because so much of their diet is fish.



This bald eagle nest (middle of the photo in background) is in a condominium community in Florida. Photo by Jerry Barrack. They also tend to build their nests away from humans, although some birds are becoming more tolerant of human activity. Bald eagles have nested for years in a condominium complex in Longboat Key in Florida, for example, for several years. Although some bald eagles have been known to build alternate nests, Thom says he has seen no signs of an alternate nest at Duke Farms.

Got a question or suggestion? E-mail Jim at wrightjamesb@gmail.com

Jim Wright writes The Bird Watcher columnist for The Record and the Herald-News. He is the author of four coffee table books about wild places, and the deputy marsh warden of the Celery Farm Natural Area in Allendale, NJ.