Bald eagles, bouncing back after years of decline, are swaggering forth with an appetite for great cormorant chicks that threatens to wipe out that bird population in the United States.
The eagles, perhaps finding less fish to eat, are flying to Maine's remote rocky islands where they've been raiding the only known nesting colonies of great cormorants in the U.S. Snatching waddling chicks from the ground and driving adults from their nests, the eagles are causing the numbers of the glossy black birds to decline from more than 250 pairs to 80 pairs since 1992.
"They're like thugs. They're like gang members. They go to these offshore islands where all these seabirds are and the birds are easy picking," said Brad Allen, a wildlife biologist with the Maine Department of Inland Fisheries and Wildlife. "These young eagles are harassing the bejesus out of all the birds, and the great cormorants have been taking it on the chin."
The recovery of the bald eagle population has been well-documented, growing from 400 pairs to more than 10,000 pairs in the lower 48 states since the 1960s. But the revival has changed the natural order of things in Maine and other states, threatening other bird species.
With more eagles around and fewer fish in the waters than in the past, young eagles are turning to other birds to satisfy their hunger. Eagles are opportunistic feeders and will go after the easiest prey they can find, bird experts say.
In Alaska, many eagles have shifted their diet from fish to seabirds. In the Midwest, they've been known to eat baby blue herons. And besides Maine's great cormorants, eagles are also feasting on baby double-breasted cormorants, gulls, eider ducks and even loons.
Nobody's raising a stink about the eagles' taste for double-breasted cormorants and gulls because those birds are so numerous and considered nuisances by many.
But the great cormorants are another matter, because their numbers in Maine are so small, said John Drury, of Vinalhaven, who's been counting seabirds on Maine islands for more than 25 years. Although the birds are widespread from Europe to eastern Canada, they are uncommon in Maine, which represents their southern range in the Northwest Atlantic.
Drury last summer counted only 80 great cormorant nests, the smallest number since 1984, the year after they were first spotted on Maine islands. Without protection, he fears the Maine population could be wiped out.
Governmental agencies and conservation groups have put countless hours and dollars toward protecting other seabird populations such as terns — but little has been done for great cormorants, he said.
"We like to have diversity of species," Drury said. "If we're going to spend all that time and energy to protect terns, then cormorants deserve as much attention."
At one time there were an estimated 50,000 pairs of bald eagles in the continental U.S. But their numbers declined from hunting and habitat loss. It was the widespread use of the pesticide DDT that almost did them in. DDT accumulated in fish, a major food source for eagles, which resulted in eagles laying eggs with weakened shells. By 1963, there were only 417 pairs of eagles left in the lower 48 states.
The bald eagle began a gradual recovery after it was listed on the federal Endangered Species list in 1967. DDT was banned in the U.S. in 1972.