Let's Talk About Birds: Bald eagles
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The American bald eagle is enjoying a resurgence.
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This is one of a series presented by the National Aviary. The National Aviary works to inspire respect for nature through an appreciation of birds.
Only 15 years ago, the American bald eagle, our national bird and the image used for the Great Seal of the United States, was threatened with extirpation in the lower 48 states. But thanks to local and national efforts, the bald eagle is experiencing a steady resurgence across the country.
At the time that Columbus landed in the New World and European settlement began, it is estimated that 100,000 bald eagles inhabited what would become the lower 48 states. By the 1800s, as settlements grew, eagle populations went into decline as the birds were targeted by farmers, hunters, ranchers and fisherman who saw them as marauders and competitors for fish and game.
The decline was further hastened when, shortly after World War II, the production of synthetic pesticides and insecticides increased, and the chemical DDT was used by farmers to control mosquitoes and other insects. DDT and its residue washed into streams, rivers and other water sources where they were absorbed by fish and aquatic plants, and then by animals that consumed the fish and plants, building up within the bodies of bald eagles. The chemical prevented the eagles from producing strong egg shells, and eggs would break during incubation or would fail to hatch.
The dangers of DDT eventually became known, in large part due to the publication of Pittsburgh native Rachel Carson's book "Silent Spring." In 1972, the Environmental Protection Agency banned the use of DDT in the United States, and bald eagle populations began to grow.
In 2007, the U.S. Fish and Wildlife Service officially removed the bald eagle from the list of endangered species, and today, Pennsylvania is home to an estimated 203 active bald eagle nests.
Bald eagles nest near large bodies of water with abundant food and old-growth trees. The shape of eagle nests are dictated by the tree in which they are built and are typically about 5 feet in diameter. Eagles often use the same nest year after year, and over that time, some nests grow enormous, reaching 9 feet in diameter and weighing upward of 2 tons.
One active nest has been identified in Allegheny County, and thanks to their distinct plumage, bald eagles can be easily identified. The adult is mainly brown with a white head and tail. Juveniles are a mottled brown, achieving their recognizable white feathering as they mature. Despite their name, bald eagles are not actually bald but take their name from the older meaning of the word, "white headed."
The National Aviary is home to three bald eagles, a female juvenile currently in training to become part of the Aviary's indoor bird show and two adult females currently on view. Learn more about them at the National Aviary on Jan. 21-22 during a special eagle weekend, featuring hands-on activities, handler talks and special activities.
First Published January 11, 2012 12:00 am
