University of Vermont

University Communications

Search

The Cormorant Conundrum

Study into managing troublesome birds takes a turn when the shooting begins

By Cheryl Dorschner Article published June 23, 2004

Cormorants
Doctoral student Adam Duerr, left, and Wildlife and Fisheries Biology Professor David Capen, along with several colleagues, study the devastation of several Lake Champlain islands wrought by overpopulation of double-crested cormorants. (Photo: Cheryl Dorschner)

Ongoing research took an unexpected turn on June 18, when Vermont Fish and Wildlife workers began shooting and trapping double-crested cormorants nesting on Lake Champlain’s state-owned Young Island, saying that other efforts have not controlled the burgeoning bird population as biologists had hoped. With federal permission, the state workers are allowed to take up to 10 percent of the troublesome colony — about 300 birds.

David Capen, a research professor, lives within view of the island and studies cormorants, but was surprised by the development. “I woke up and saw through my spotting scope there were no birds on the nests and cormorants everywhere in the sky. I had no idea what was going on,” he says. “When I got in the boat I thought I was going to chase someone off the island. Then I saw the wildlife services boat.”

Capen has been tracking these birds since 1995, as have fellow UVM scientists Therese Donovan, Donna Parrish and doctoral candidate Adam Duerr, along with Cornell University Professor Milo Richmond and others. The cooperative project has nearly $200,000 in current funding, including money from the fish and wildlife department. Other money is from the Lake Champlain Sea Grant and the Berryman Institute.

Neutral observation
Capen doesn’t take sides on the issue of controlling the population of this species through shooting.

“Our role is to provide the scientific evidence to help wildlife managers make informed decisions,” says Capen. “Purely from the research standpoint, it’s fine (that they’re shooting). We now have the opportunity to test what has only been an opinion of ours — that disturbing the colony will cause the surviving birds to abandon the colony and relocate — the real test will be next year. My guess is that the numbers in this colony will drop much lower than the number they shoot. And I’m sure we’ll see more birds on Four Brothers, Missisquoi, Crown Point and in Quebec, Ontario and western New York.”

The cormorant study involves other scientists in these locations and who report sightings of banded birds. All totaled, UVM researchers have put identification bands on some 1,200 birds that inhabit this area of Lake Champlain — 724 currently residing in the area.

“If they show up elsewhere, we’ll know why. We already got a report from Quebec of four bird sightings after Friday’s shooting,” Capen said. And this week, we’ve seen birds from Oneida Lake (New York) that are looking for a place to breed. These birds are traveling far.”

Duerr agrees, saying, “The biggest advantage we have is that we have a cooperative effort with several areas in New York and Canada and we share information and sightings. The whole point of the studies is to see how management affects the bird population.”

Duerr and Capen were surprised last weekend when they arrived on Young Island to band birds and found the whole colony acting strangely, mating and building nests as if it were April instead of June.

As a population-management technique, eggs on Young Island had been sprayed with a light film of corn oil to stop them from hatching without interrupting the birds’ nesting activity — the lack of interruption is important, because if these birds abandon their nests, they will build another one and lay more eggs. The shooting caused the survivors to abandon their nests, possibly to breed again.

“The question is, can they lay a new clutch of eggs and hatch and fledge those birds by the end of September? They’re right at the edge of their ability to do that given the calendar,” says Duerr.

The cormorant conundrum
Of the estimated 20,000 cormorants that inhabit this area of Lake Champlain, Capen estimates that 98 percent reside on Young and nearby Four Brothers islands — an area of barely eight acres. Four Brothers is just 20 miles away as the cormorant flies and is owned by the Nature Conservancy, which has chosen not to oil these nests. While most native and rare bird species have left Young Island, Four Brothers is home to black crowned night heron, cattle egret, great egrets — “perhaps the only ones in the Lake Champlain area,” says Capen, and glossy ibis. Both islands are home to the rare Caspian tern.

“By disturbing nests, I think (the state is) going to be putting at risk the birds that they’re trying to save,” Capen says. “Just because these birds are in somebody else’s jurisdiction doesn’t mean they shouldn’t be concerned. Otherwise I wouldn’t object to this approach.”

The primary reason for trying to control this waterfowl, which is a nuisance along both coasts and on several large lakes, is its ability to devastate a habitat quickly and force out other species. Just six years ago the two Lake Champlain islands were lush with basswoods and white pines and verdant undergrowth. Now the steep, sandy cliffs are held together only by a tough growth of burdock and stinging nettles. The earth and the silver bones of these tree-forms are covered with the white chalky guano. In addition to the chalky dust, the air is filled with a sound best described by the birders bible The Sibley Guide to Birds as “hoarse bullfrog-like grunting.”

“Running out of food supply is the only thing that will curtail the population,” Capen says. "And that is unlikely for a long time. But for now, we’ve got a lot of banded birds out there, and we’ve got a very good chance of documenting any management technique’s effect.”

And so the scientist waits and watches to find out what the latest chapter of the cormorant saga will bring.