In the United States, there may be no greater avian icon — or impressive wildlife comeback story — than the Bald Eagle.
The shaggy, fierce-eyed bird has been our national symbol since 1782. It wasn't until the 1960s and 1970s that Bald Eagles became an emblem of the environmental movement as their numbers plummeted from the effects of the pesticide DDT. Once DDT was banned and the species was fully protected under the fledgling Endangered Species Act, however, eagle numbers began to rebound, gradually at first and then with increasing vigor. In 2007, the U.S. Fish and Wildlife Service removed the Bald Eagle from the federal endangered species list.
But what did “delisting” truly mean for Bald Eagles? And a decade later, where does the species stand?
Developed in the 1940s, DDT — short for dichloro-diphenyl-trichloroethane — was one of the first synthetic insecticides. Its effectiveness made it popular, but it came at a cost: DDT residue began to wash off agricultural fields and into aquatic ecosystems, and soon Bald Eagles and other large predatory birds across the country were eating contaminated fish. Ingesting the chemicals caused eagle eggshells to become so thin that large numbers of nests failed.
Rachel Carson's seminal 1962 book Silent Spring helped to spark the environmental movement and exposed the hazards of rampant pesticide use on birds and other wildlife. The Environmental Protection Agency eventually banned DDT a decade later, just two years after the agency was established.
Legal protection of Bald Eagles themselves proceeded in a more piecemeal fashion. It began with the passage of the federal Migratory Bird Treaty Act in 1918. Then, in 1940, the Bald Eagle Protection Act (now the Bald and Golden Eagle Protection Act) expanded the law's reach, prohibiting the killing or possession of Bald Eagles or their feathers, eggs, or nests. Some eagle populations were listed under the Endangered Species Preservation Act, which became law in 1967; this protection was maintained with the passage of the Endangered Species Act (ESA) in 1973.
Finally, in 1978, ESA protection expanded to include Bald Eagles in all 48 contiguous states. (The eagle population in Alaska had remained healthy, and was never in need of listing.) The resulting efforts to restore the species went beyond the simple elimination of DDT use: eagles' nests and habitat were now strictly protected from human disturbance of all sorts.
It worked. In 1963, when the species was at its lowest ebb, there were only an estimated 417 breeding pairs of Bald Eagles in the lower 48 states. By 1997, this number had increased to more than 5,000.
The Fish and Wildlife Service proposed “delisting” the Bald Eagle in 1999, based on the fact that recovery goals for all regions of the country had largely been met a decade before — and populations were still on the rise. In 2007, it became official: the Bald Eagle was no longer endangered, or even threatened. Our national emblem was back.
Taking the Bald Eagle off the endangered species list didn't mean an end to federal regulations concerning the management of the species. It just meant their management was once again governed solely by the Bald and Golden Eagle Protection Act.
The Fish and Wildlife Service now needed to create a whole new set of regulations governing the killing, capturing, or otherwise harming of a protected species. (In regulatory terms, this is known as “take” of a species.) No one wants to see an eagle killed by human activity. The question confronting federal officials and conservationists alike was — and remains — how much take is too much?
The Bald and Golden Eagle Protection Act gives the government the ability to issue permits to take eagles as long as it's compatible with the preservation of the species. “But it didn't define what that meant,” says Brian Millsap, the Fish and Wildlife Service's National Raptor Coordinator. “So when Bald Eagles were delisted, we defined the preservation of the species as maintaining stable breeding populations. That's a conservative management objective — not only are we not going to let them go extinct, we're going to try and maintain populations at at least the size they are now.”
In 2016, the Fish and Wildlife Service issued updated regulations governing the take of eagles and eagle nests. ABC, which had sued the Service in 2014 over the previous version of this rule, pushed successfully for the 2016 regulation to require greater public involvement in the permitting process and that wind energy companies have independent, third-party monitoring at their facilities, which are often deadly to eagles and other birds.
“Bald Eagles are rebounding, but they're still well below their historic numbers,” says Steve Holmer, ABC's Vice President of Policy. “We have to stay vigilant. And now that eagles are off the endangered species list, that means keeping a close watch on how they're being managed.”
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Even with new regulations in place, monitoring is crucial to ensuring everything is working as it should. An ambitious federal plan to survey the entire continent every five years to estimate the number of occupied nests stumbled due to lack of funding after its initial implementation in 2009. But even that single estimate showed a further substantial increase in the population since delisting two years before: Bald Eagles were estimated to number more than 72,000 individuals in the lower 48 states, and nearly 143,000 including Alaska. Millsap says a second round of surveys is occurring right now. The plan is to have surveys take place every three years from now on.
Other sources of data can hint at what's going on with Bald Eagles, too. The North American Breeding Bird Survey, overseen by the U.S. Geological Survey and their counterparts in Canada, dispatches skilled volunteers to count birds along set routes across the continent during the breeding season each spring.
The 2016 data showed a 5 percent annual increase in Bald Eagle numbers across the continent. “We'll see what that translates into in terms of nesting pairs when we complete the survey we're doing right now,” Millsap says. “But the data that we have suggests that Bald Eagle populations not only increased from delisting until 2009, but that they've continued to increase since then.”
The eagle population boom will almost certainly flatten out eventually. When it does, it may be due to the species naturally hitting its carrying capacity — a term used in ecology to define the maximum population size a region's resources can sustainably support. But wildlife managers remain on the alert for new threats. While DDT may be a thing of the past, other toxins both new and old continue to worry those charged with ensuring Bald Eagles' continued success.
Although they hunt fish and other prey, Bald Eagles are also frequent scavengers, and a gut pile left behind by a game hunter represents a tempting meal. These carcasses often contain fragments of lead ammunition, which eagles and other scavengers gulp down along with the meat. Even very small amounts of lead contamination in scavenged meat can be enough to kill an eagle.
The lead problem isn't new. It helped motivate the banning of lead shot for waterfowl hunting in 1991, which reduced Bald Eagles' exposure in the wetlands and lakes that are their preferred habitat. However, as populations have grown, more and more individuals have moved into upland areas where the hunting of deer and other large animals is common. Mercury, another heavy metal, is also raising alarms for predator species around the world as it accumulates up food chains.
Other pesticides whose effects aren't yet well understood have entered the market, such as brodifacoum, one of a broader class of chemicals known as second-generation anticoagulant rodenticides, or SGARs. Although there were only five known Bald Eagle deaths from brodifacoum poisoning between 1982 and 2013, compared to 484 from lead, it's beginning to show up at chronic low levels in even the most isolated Bald Eagle populations, which wildlife managers are at a loss to explain.
While the future is impossible to foretell, people who know Bald Eagles the best are optimistic about what's ahead. So says Bryan Watts, Director of Virginia's Center for Conservation Biology and a professor at the College of William and Mary, who studies Bald Eagles of the Chesapeake Bay region. “Eagles aren't going away,” Watts says.
It's impossible to see an adult Bald Eagle soaring overhead without feeling something — a flash of recognition, or maybe even a surge of hope. Thanks to a patchwork of environmental laws and the efforts of scientists, conservationists, and government agencies, more of us have the chance to experience that today than at any time in the past half-century.
ABC's Holmer says the Bald Eagle's rebound doesn't have to be such a singular victory. There are many more success stories waiting to happen: 41 U.S. bird populations listed under the Endangered Species Act are showing upward trends, he notes, making their recovery a real possibility. For now, though, the Bald Eagle remains a star.
“Bald Eagle recovery is one of the greatest success stories in our nation's history,” Watts says. “We should all be proud that we collectively made a responsible decision about the future of this species that Americans care an awful lot about.”
This article first appeared in the spring 2018 edition of Bird Conservation magazine.
Rebecca Heisman is a science writer based in Walla Walla, Wash.