Bald Eagle
(Haliaeetus leucocephalus)
Legislation and legal protections were successful in bringing the Bald Eagle back from the brink, proving that conservation efforts can and do work.
The majestic Bald Eagle was adopted as the national symbol of the United States in the late 1700s, not long after our country was born. Abundant and widespread, these birds were often seen soaring the skies and plunging into lakes and rivers after fish, their preferred food. As a national treasure, eagles were protected by law from early in the 1900s, and those protections were strengthened with passing of the Bald Eagle Protection Act in 1940. That act made it a crime to take eagles or their parts, including feathers, nests or eggs.
Despite these legal protections, eagle populations began declining precipitously in the middle of the 20th Century. The culprit was not hunting or even habitat loss, but rather poisoning. As agricultural practices changed in North America, the use of pesticides like DDT became widespread. These pesticides would run off the fields and into streams and lakes. There they were consumed and absorbed by aquatic insects, which in turn were consumed by small fish, which in turn were consumed by larger fish. With each step up the food chain, the pesticides became more concentrated, reaching very high concentrations in the tissues of the large fish taken by eagles.
Eagles were rarely killed outright by eating DDT-laced fish. Rather, the toxins altered the egg-production machinery of females, leading them to lay eggs with paper-thin shells. These eggs were fragile, breaking easily when jostled in the nest, and few survived to hatching.
Eagle reproduction, and eagle populations, plummeted. By 1962, only 417 breeding pairs of Bald Eagles remained in the lower 48. Rachel Carson’s seminal 1962 book Silent Spring was a warning cry about the devastating effects that DDT and other pesticides had on birds, including Bald Eagles. Thanks to a groundswell of public support, the use of DDT was banned in 1972. Just a few years later, Bald Eagles were given additional protection under the Endangered Species Act.
Legislation aimed at the root causes of population declines and the enforcement of legal protection worked! Eagle numbers rebounded, and the Bald Eagle was removed from the Endangered Species List in 2007.
The U.S. Fish and Wildlife Service (USFWS) has now been assembling counts of Bald Eagles for over fifty years, tracking the recovery through counts from states and by aerial surveys. The 2018-19 bald eagle population report found a robust quadruple increase in the Bald Eagle population from just ten years earlier.
This rising number of Bald Eagles undoubtedly reflects the continuing conservation success story that began with banning DDT, but it also represents a major advance in using participatory science-powered supercomputing to generate better population estimates. For this latest count, the federal government collaborated for the first time with the Cornell Lab of Ornithology to augment their aerial surveys with a big-data population model generated by eBird, which is built on participatory science. More than 180,000 birders shared data with the Cornell Lab by uploading eBird checklists, which scientists at the Lab then used to develop a model for areas that USFWS could not cover in their aerial surveys. Through public participation in this kind of science, we can all play a part in the continued success story of our national symbol.