Bald Eagle Bounces Back After Decades of Persecution

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After studies showed that salmon populations were not harmed by eagle predation, this law ended a bounty system in Alaska that claimed 128,000 eagles between 1917 and 1952. The actual number of slaughtered eagles probably exceeded 150,000, since many bounties were never collected.

For a long time, the Bald Eagle Protection Act, designed also to protect the beleaguered golden eagle, was not strictly enforced. At one Wyoming ranch, for example, eagles were systematically shot for their perceived threat to livestock. According to a 1970 report, more than 770 bald eagles were shot at this ranch, and hunters were paid $25 for each carcass. Responding to a public outcry over such flagrant violations, the government began to crack down.

Just when it was finally benefiting from legal protections, the bald eagle took a heavy blow from DDT, a pesticide that enters the food chain and causes reproductive failure. Widely used after World War II to control mosquitoes and other insects, DDT was wreaking havoc among many bird species. Raptors were particularly vulnerable—over time, animals higher in the food chain accumulate more DDT.

New research on the effects of DDT challenges the long-held belief that eggshell thinning was the primary cause of reproductive failure in birds. "The thinning did occur," said Buehler, "but it was probably not actually responsible for the reproductive failure."

Rachel Carson exposed DDT poisoning in her 1962 book, Silent Spring. The pesticide was banned in the United States in 1972, but by then, over a period of about 20 years, it had done damage comparable to 175 years of persecution. The bald eagle hit a low point in 1963, when a nesting survey in the lower 48 states found only 417 pairs.

The most sweeping protections took effect in 1978, when, under the Endangered Species Act of 1973, the bald eagle was listed as endangered in 43 of the lower 48 states and as threatened in the rest. The estimated 50,000 bald eagles in Alaska are not at risk; therefore, they do not receive protection under the act.

Enforcement of the Endangered Species Act; cooperation among wildlife agencies and conservation organizations on captive-breeding programs and reintroductions; and citizen support led to a fourfold increase in lower-48 nesting populations between the mid-1970s and mid-1990s. In 1995, the U.S. Fish and Wildlife Service downgraded the bald eagle's endangered-species status in all of these states—at present, it is listed as threatened.

With the number of nesting pairs now exceeding 6,000—only Rhode Island and Vermont lack breeding populations—the Fish and Wildlife Service has announced plans to "delist" the bald eagle entirely and is working out the details of a management plan. After delisting occurs, the eagle will still be protected under the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act. Many states have laws that continue to protect the eagle as an endangered, threatened, or "special concern" species.

A Great Conservation Story

The current bald eagle population is estimated at 100,000; more than half the birds are found in Alaska and British Columbia. Eagles will never be as abundant as they were before the arrival of Europeans. Nonetheless, their comeback is one of the great conservation stories.

Their continued success requires vigilance: Threats include oil spills—the Exxon Valdez spill in 1989 killed some 250 eagles, and the local population did not recover until 1995. Poisoning from lead fishing sinkers has also been implicated in eagle deaths. As humans encroach on eagle habitat, and vice versa, collisions with man-made structures and with vehicles are expected to rise.

Meanwhile, the National Wildlife Health Center in Madison, Wisconsin is monitoring outbreaks of avian vacuolar myelinopathy, a fatal neurological disease that first showed up in bald eagles and coots wintering at DeGray Lake in Arkansas in 1994. Twenty-nine eagles died that year; the disease has since been identified at 11 lakes in 5 states.

"We still have not been able to determine the etiology [causes] of the disease, although we suspect a chemical substance of unknown origin, most likely natural or microbial," said Tonie E. Rocke of the NWHC. "We also suspect that eagles acquire the disease secondarily through consumption of affected prey—coots and waterfowl."

As their numbers grow, bald eagles can be expected to expand their breeding range, within limits imposed by habitat destruction, human disturbance, and environmental contamination.

"Persecution from humans has declined in the last 20 years, and prime wilderness habitat has become occupied," said David Buehler, "so eagles have started moving back into human-developed areas."

Robert Winkler, a nature writer, is working on a book about his adventures with birds in the "suburban wilderness" of southern New England. Visit him at his Web site.

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