Bald Eagle Ddt Case Study

Bald eagles have made a resurgence in the United States because of a ban on DDT and protection provided by the Endangered Species Act. Despite the bird's booming populations, biologists are concerned that prime eagle habitat is rapidly being taken over by development. Lindsay Mangum, NPR hide caption

toggle caption
Lindsay Mangum, NPR

Bald eagles have made a resurgence in the United States because of a ban on DDT and protection provided by the Endangered Species Act. Despite the bird's booming populations, biologists are concerned that prime eagle habitat is rapidly being taken over by development.

Lindsay Mangum, NPR

The Chesapeake Bay region is home to almost 1,000 pairs of bald eagles — up from 60 pairs 30 years ago. Lindsay Mangum, NPR/Source: Bryan D. Watts, Center for Conservation Biology, College of William and Mary. hide caption

Click on the map to see eagle nesting patterns.
toggle caption
Lindsay Mangum, NPR/Source: Bryan D. Watts, Center for Conservation Biology, College of William and Mary.

An eagle flies from its nesting site on the Potomac River. Thousands of eagles migrate to the Chesapeake Bay each year from Florida, New England, and Canada. Bryan Watts hide caption

toggle caption
Bryan Watts

An eagle flies from its nesting site on the Potomac River. Thousands of eagles migrate to the Chesapeake Bay each year from Florida, New England, and Canada.

Bryan Watts

Biologist Bryan Watts has been tracking eagles on the Chesapeake Bay for more than 20 years. From a small plane, he scouts the trees below for nesting sites. Elizabeth Shogren, NPR hide caption

toggle caption
Elizabeth Shogren, NPR

Biologist Bryan Watts has been tracking eagles on the Chesapeake Bay for more than 20 years. From a small plane, he scouts the trees below for nesting sites.

Elizabeth Shogren, NPR

Biologists are worried that new developments along the Potomac River will displace the eagles that have nested along the banks. Eighty percent of the eagles in the region nest on private property. Bryan Watts hide caption

toggle caption
Bryan Watts

Biologists are worried that new developments along the Potomac River will displace the eagles that have nested along the banks. Eighty percent of the eagles in the region nest on private property.

Bryan Watts

A new development built in prime nesting habitat along the Potomac River. Bryan Watts hide caption

toggle caption
Bryan Watts

A new development built in prime nesting habitat along the Potomac River.

Bryan Watts

As the federal government gears up to take the bald eagle off the endangered species list, biologists worry that the fast pace of waterfront development in key eagle habitat could make the majestic bird's robust numbers fleeting.

Just as the eagle is returning to its riparian roosts, people are snapping up waterfront properties at record numbers, experts say.

"There's a thin ribbon of land that both populations are really vying for," says Bryan Watts, a biologist at the College of William and Mary's Center for Conservation Biology. "Everybody wants to live along the waterfront. That's true of us — that's also true of eagles."

To get a close-up view of the problem, Watts takes to the skies on an aerial tour of eagle habitat. In a four-seater Cessna, Watts hugs the shorelines of the Potomac River south of Washington, D.C., at a low altitude of 200 to 300 feet.

Near the Chesapeake Bay, the Potomac is wide — four miles across in some places. Watts says this is some of the most important habitat for bald eagles in the country. The eagles that live here represent a large portion of the 7,000 eagle pairs that currently breed in the lower 48 states.

Eagles are everywhere along the rural and sparsely populated stretches of the river and its tributaries. In addition to a vibrant population of resident birds that breed here annually, thousands of other eagles use the area as an essential feeding ground.

Birds from Florida fly up in the summer and birds from Canada and New England fly south in the winter. The Chesapeake Bay region provides a comfortable climate and plenty of food. Below, Watts spots a solitary eagle standing on the frozen river, finishing a meal of duck.

For 20 years, Watts has been flying over this area, studying the return of the eagle to the Chesapeake Bay. The number of nesting pairs has soared to nearly 1,000, from a low of 60.

During his flights, Watts sees hundreds of eagles. Many adults — with chocolate wings and bright white heads and tails — sit on nests, incubating eggs. Eagles are territorial when they're brooding, but some of the nests are as close as only a quarter-mile apart. Watts points out the very high breeding density in rural areas close to large creeks.

Unfortunately for the eagles, they aren't the only ones who want to build their homes along this waterfront.

"It's just point after point being consumed by development here," Watts says. "It's just like a wave that's running right down the Potomac. And the land values are just going out of sight here. Look at all of the open patches here that have just been cleared in the last year for new development... thousands of units that are going to go in shortly here."

Watts says that when people move in, eagles move out. Only 4 percent of the eagles in Virginia nest close to developed areas.

Below, a new development high on a bluff overlooks the Potomac. Watts says eagles used to nest here. He points out a few vacant lots at the end of a cul-de-sac. Watts says the developer was restricted from building on these lots because they were close to an eagle nest.

The nest has been abandoned for two years since the development went in, Watts says, and the developer now will be able to build houses on those lots.

Watts worries that the pace of construction will pick up if the eagle loses the protection of the Endangered Species Act, as expected. Another law, the Bald and Golden Eagle Protection Act, would take over but there is concern that it won't do as much to protect nests and may not protect feeding areas at all.

Decisions about whether to develop private land will be crucial to the eagle's future because very little of the eagle's habitat is protected within wildlife refuges or parks. Watts says about 80 percent of the eagles in the Chesapeake Bay region nest on private property.

Without the safeguards of habitat, Watts predicts that the Chesapeake Bay eagle population will decline in the next three or four decades.

Changes in the Chesapeake Bay habitat will not just affect local eagles, Watts warns. Because eagles from the whole Atlantic Coast use this area, fewer eagles in the Chesapeake Bay will mean fewer eagles from Canada to Florida.

The first of a two-part series.

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.

Recent Bird Stories by National Geographic News

Birder's Journal: It's Survey Season for Breeding Birds
Birder's Journal: Chasing Down Warblers
Africa's New Safari Trend Is for the Birds
Decline of Red-Tailed Hawks Has U.S. Scientists Puzzled
A Reason to Give Thanks: The Return of the Wild Turkey
State Bird of Hawaii Unmasked as Canadian
Harry Potter Owl Scenes Alarm Animal Advocates
Ultrarare Woodpecker Spurs Ultimate Birding Trip
"Extinct" Woodpecker Still Elusive, But Signs Are Good
Extinct Dodo Related to Pigeons, DNA Shows
Bird Extinctions May Hold Clues to Human Survival, Author Says
Tagging Hobbles Penguins, Some Researchers in Cape Town Contend
Patagonia Penguins Make a Comeback
Penguin Decline in Antarctica Linked With Climate Change
Ice Buildup Hampers Penguin Breeding in Antarctica
Evolutionary Oddities: Duck Sex Organ, Lizard Tongue
Some Ducks Let Young Be Raised by Relatives
Turkey Vultures Flourish in the U.S. Thanks to Road Kill
Forecasting the Journey South

National Geographic Bird Resources

Bald Eagles: Come Back From the Brink
Experience the Sights and Sounds of Eagles

Nationalgeographic.com Bird-Watching Sites

North Carolina's Outer Banks
South Dakota's Black Hills
Santa Fe Area
San Francisco Area
Rocky Mountain National Park
Philadelphia Area
New York City Area
Chicago Area
Boston Area
Yellowstone National Park
Florida Keys Area

From the National Geographic Store

Guide to North American Birds
Portable Birdsong Identifier
Birder's Journal
Songbirds Puzzle



0 thoughts on “Bald Eagle Ddt Case Study

Leave a Reply

Your email address will not be published. Required fields are marked *