Bald Eagle Fights Don't Mean Habitat Is Full, Experts Say
for National Geographic News
|May 3, 2006|
Recent violent territorial disputes among bald eagles in the Chesapeake
Bay could be nature's way of controlling the birds' increasing numbers,
But, they add, there is still enough habitat in the region for nesting, and despite media reports, the conflicts may not be a nationwide pattern.
"For every population there is a gradient of habitat," said Greg Butcher, director of bird conservation at the National Audubon Society.
"In other words, there is the best habitat and the good habitat, which is not as good as the best.
"So what we're seeing [with the eagles] is competition for prime location. It doesn't really mean all the habitat has been used up."
According to government estimates, about 7,000 nesting pairs of bald eagles now exist in the wild (see bald eagle photos).
Experts say the population will continue to rise and that the birds' habitat has yet to reach full capacity in many regions of the country.
"I think this conflict is something that is only found where the eagles are doing so wellas in the Chesapeakethat nest sites or territories are in short supply," said Laurie Goodrich of the Hawk Mountain Sanctuary Association in Kempton, Pennsylvania.
"I am not sure it warrants the drama of the headlines."
The bald eagle was first listed under the U.S. Endangered Species Act in 1967 but only in the lower 48 statesthe species has never been endangered in Alaska.
Bald eagle numbers have been steadily rising since the U.S. Environmental Protection Agency banned the insecticide DDT in 1972.
DDT had been devastating the populations of many bird species. The chemical disrupts the females' ability to process calcium, leading to thinner eggshells that break easily during incubation (related photo: spraying DDT on a beach in 1945).
Jim Fraser is a professor of fisheries and wildlife sciences at Virginia Institute of Technology in Blacksburg.
He is among the experts who say the eagles' recent battles over the Chesapeake could be nature's way of keeping checks and balances on the birds' rising numbers.
Populations of some species, such as snowshoe hares, are kept in check largely by food limitation, while others are controlled by predation.
In eagles, it appears that territorial strife plays a role in limiting population growth, Fraser explains.
"I don't think of this so much as eagles being victims of their own success," Fraser said, "as that natural processes are beginning to limit eagle populations that previously had been limited by reproductive failures induced by contaminants by poisoning or by human persecution."
Bald eagles were reclassified from "endangered" to "threatened" in 1995, and their steadily rising numbers have the federal government now considering the birds' removal from the endangered list.
Some experts support the government's action, including Michael Bean, chair of the wildlife program at the New York-based nonprofit Environmental Defense.
But he notes that other increasing species will require many more years before they can be taken off the list.
"California condors, whooping cranes, California sea otters, and many other species have also significantly increased their numbers," he said. "But they all have a considerable distance to go before they can be considered safely recovered."
While the frequency of conflicts among eagles may be expected to increase as eagle densities increase, he says, it hasn't yet stopped eagle populations from growing in any of the lower 48 states.
"[Bald eagles] too may someday find themselves sufficiently numerous that they compete for space. If that is a problem, it is one most currently rare species should be happy to have," he added.
Protect Habitat Too
In general, most experts agree that bulging numbers of bald eagles is a conservation success story.
"The big picture is that there is very healthy population increase in bald eagles, and we have to celebrate that," said Audubon's Butcher.
"As a fish-eater, the bald eagle is at the high end of a very long food chain, and for it to do so well is a good sign for the aquatic ecosystem," Butcher added.
He thinks that the Bald Eagle Protection Act of 1940 will still provide an umbrella for the birds if they are removed from the endangered species list.
Of greater concern, he says, is protection of shorefront eagle habitat, especially in the Chesapeake (Chesapeake Bay interactive map).
"The Chesapeake Bay is under tremendous human stress. Recently scientists discovered a serious disease in rockfish, and that might affect the eagles," he said.
"If we don't take care of the Chesapeake so that fish populations are healthy, the bald eagles won't be healthy, either."
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