How Did the Bald Eagle Recover? From DDT to Delisting

How many bald eagles were there before the decline?

Nobody counted eagles before the 20th century, so early numbers are only rough estimates. One frequently quoted guess is that several hundred thousand bald eagles lived in what is now the United States and Canada before European settlement. The species nested along almost every large river, lake and coastline.

Numbers began to fall in the 1800s. Eagles were shot as supposed threats to livestock and fish, and Alaska even paid a bounty on them from 1917 until 1953, during which more than 100,000 eagles were killed there. Large waterside trees were also cut down for timber and development.

Why bald eagles nearly disappeared

Three main factors pushed the bald eagle to the edge in the lower 48 states:

• Shooting and persecution. Despite the Bald Eagle Protection Act of 1940, illegal shooting remained a leading cause of death for decades.
• Habitat loss. Shoreline development removed the tall trees and quiet areas eagles need for nesting.
• DDT. This insecticide came into widespread use after World War II. It washed into rivers and lakes, built up in fish and became concentrated in fish-eating birds, a process called biomagnification.

DDT itself rarely killed adult eagles. Instead, its breakdown product DDE disrupted how females built calcium into their eggshells. The eggs were too thin to support an incubating parent and often cracked or failed to hatch. Pairs kept nesting but raised few or no young, so the population aged and shrank. By 1963 a national survey found only about 417 nesting pairs in the lower 48 states, with remaining strongholds in Florida, the Chesapeake Bay and the upper Midwest.

Rachel Carson’s 1962 book Silent Spring brought the harm caused by DDT and other pesticides to public attention and helped build the political pressure for change.

The rescue: laws, the DDT ban and the Endangered Species Act

Recovery was the result of several actions working together:

The DDT ban was the turning point. Once DDT levels in fish began to fall, eggshells thickened again and breeding success climbed. The Endangered Species Act added strong protection for nest sites and winter roosts, and guidelines kept logging, building and boating away from active nests during the breeding season.

Reintroduction and nest protection

In states where eagles had almost vanished, wildlife agencies gave nature a helping hand. Young eaglets from healthier populations in Alaska, Canada and elsewhere were moved to artificial nest platforms in suitable habitat and fed without seeing people until they could fly, a technique called hacking. Because eagles tend to return to breed near where they fledged, these birds later settled and nested in their new home. New York ran one of the best-known programs from 1976 to 1988.

Other efforts included protecting nest trees, closing areas around nests during the breeding season, cleaning up polluted waters and educating the public. Many wildlife refuges, such as those along the Mississippi River and Chesapeake Bay, became important breeding and wintering sites.

The comeback in numbers

The results were dramatic. From about 417 pairs in 1963, the lower 48 states held around 10,000 breeding pairs by 2007, when the bald eagle was removed from the endangered species list. A US Fish and Wildlife Service report published in 2021, based on 2019 surveys, estimated about 316,700 bald eagles, including some 71,400 breeding pairs, in the lower 48 states alone.

Today bald eagles nest in every one of the lower 48 states and have returned to cities such as Philadelphia, Washington, D.C., and Toronto. Globally the species is listed as Least Concern by the IUCN, with an increasing population. The bald eagle, along with the peregrine falcon, osprey and brown pelican, is now one of the best-known success stories of the Endangered Species Act. That history is part of why it remains such a powerful emblem; see why is the bald eagle the national bird?.

Threats that remain today

Delisting did not end protection. The bald eagle is still covered by the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act, which forbid killing or disturbing eagles and their nests without a permit. Monitoring continues to make sure numbers stay healthy.

The main modern threats are:

• Lead poisoning from fragments of lead ammunition in carcasses and gut piles, and from lead fishing tackle. A 2022 study in Science found repeated lead exposure in close to half of the bald eagles sampled across 38 states.
• Collisions with vehicles, power lines and wind turbines, and electrocution on power poles.
• Disease, including the highly pathogenic avian influenza that killed many bald eagles in several states during the 2022 outbreak.
• Disturbance of nest sites as eagles move into busier areas.

Because eagles live long and breed slowly, even moderate increases in adult deaths can matter. For how long individual eagles survive, see how long do eagles live?.