BANGOR (AP) – Getting an eaglet out of a tall tree as part of a survey of the effects of pollution on eagles is no easy task.

First, Chris DeSorbo carefully inched up a 75-foot white pine. Next, he had to get the feisty eaglet into a canvas sack. Twenty minutes later, the unhappy bird was lowered by rope into the hands of DeSorbo’s partner on the ground.

Chris Niven attached metal identification bands to the bird’s legs before taking blood and feather samples. Then it was back to the nest.

Researchers with the U.S. Fish and Wildlife Service, Maine Department of Inland Fisheries and Wildlife, FPL Energy-Maine Hydro and the Gorham-based BioDiversity Research Institute are studying how much pollution is affecting Maine’s eagle population.

Thirty years ago, a biologist could have scoured all of Maine for months and found fewer hatchlings than DeSorbo handled in two afternoons.

These days, Maine is home to an estimated 400-plus pairs of breeding bald eagles, according to aerial surveys. That represents 90 percent of the eagles in New England.

“Everybody looks to Maine to be the stronghold in the Northeast, and we take that role very seriously,” said Charlie Todd, the top eagle biologist with the Maine Department of Inland Fisheries and Wildlife.

The effort to study the effect of pollution on eagles will continue for several years.

Earlier this year, Steve Mierzykowski of the Fish and Wildlife Service removed the livers of more than a dozen dead eagles for analysis for a variety of contaminants, including mercury, dioxin and pesticides. The pesticide DDT was largely blamed for the dramatic population decline in eagle populations in the 1960s and 1970s.

That same research project brought Niven, DeSorbo and Mierzykowski to the eagle’s nest on a Penobscot County pond earlier this month.

Instead of liver samples, the group was collecting blood samples from eagle nestlings all over the state to compare mercury levels in different habitats.

DeSorbo, who is using the mercury program as his master’s thesis from Antioch New England Graduate School in Keene, N.H., suited up in a rock climber’s ropes, harnesses and helmet before beginning his ascent.

Contrary to their reputations as fierce predators, adult eagles generally circle overhead but do not bother the climbers, even when they remove the eaglets from the nest.

“Actually, they are quite passive birds,” DeSorbo said. “Ospreys will hit, and a lot of other raptors will hit you. But I haven’t had an adult eagle come at me.”

Getting at the eaglets is tricky, though. DeSorbo and Niven, who’re from the BioDiversity Research Institute, have to be careful to time their visits when the eagles are small enough to be handled and too young to fly.

The eaglet found in the 75-foot tree appeared healthy as he tried to bite Niven, Mierzykowski and a camera lens. Weighing in at nearly 10 pounds, the young eagle appeared to be well fed.

The federal government is expected to remove the bald eagle from the list of threatened species either this year or next. Nationwide, there are more than 7,000 nesting pairs. But eagles will remain protected under the federal Bald and Golden Eagle Protection Act.

Maine may opt to keep the eagle’s “threatened” designation in Maine. That decision remains to be seen, Todd said.