There are now more than 10,000 pairs, according to the U.S. Fish and Wildlife Service. Maine's 500 pairs represent the largest population in the Northeast, up from less than 30 pairs in the 1960s. New Hampshire has about a dozen pairs and Vermont has one. Minnesota, Wisconsin and Florida each have more than 1,000 pairs of bald eagles, the agency said.
The bald eagle was taken off the federal endangered species list two years ago; Gov. John Baldacci is set to sign a bill this month taking it off Maine's endangered and threatened species list.
But all those eagles need to eat.
In the Midwest, eagles have targeted young blue herons, said Jody Millar, the national eagle recovery coordinator for Fish and Wildlife, based in Moline, Ill.
And in Alaska, researchers have documented a shift in bald eagles' diet from fish to marine birds that's linked to changes in the coastal ecosystem.
A growing number of killer whales caused a chain of ecological events that reduced the number of otters and amount of kelp providing habitat for fish, Robert Anthony reported in the journal Ecology. With fewer fish and baby otters to eat, eagles began raiding nests of other birds.
In Maine, eagles have been spotted eating loon chicks and have occasionally been known to carry off adult loons, said Sally Stockwell, director of conservation at Maine Audubon.
Off the coast, eagles have taken to eating all types of seabirds on rocky remote islands and ledges where, in years past, the seabirds didn't have any predators. If fish — the eagles' natural diet — were more plentiful, perhaps they wouldn't be so inclined to go after other birds, Drury said.
"They'll catch whatever is easiest to catch," he said. "There are more birds now and less fish."
Drury was on Seal Island last week to chase bald eagles away from cormorant nests. Besides eating the babies, eagles are driving the adults from their nests, leaving the eggs exposed to other predators, he said. The eggs will hatch in late May or early June, and the chicks will learn to fly by mid-August, he said.
Greg Butcher, director of bird conservation for the National Audubon Society in Washington, hasn't heard of the eagle resurgence affecting bird populations elsewhere, but said he wouldn't be surprised if it's happening. Whatever the case, it is sure to generate debate among the nation's millions of birders, he said.
"We're in an interesting age where most people think birds are either overabundant or too rare," he said. "It's hard to get it just right."