At left: Workers with the United States Department of Agriculture Wildlife Services apply oil to eggs in cormorant nests while tallying the number of nests on an island in the Les Cheneaux Islands. Paint markings on the nests help the workers keep track of which nests they have already counted. (Photograph courtesy of USDA Wildlife Services) More aggressive federal control of double-crested cormorants this year includes killing 50 percent of breeding birds and oiling all eggs found in the Les Cheneaux Islands. Smaller-scale projects are underway in Thunder Bay at Alpena and Big and Little Bays de Noc near Escanaba.

In addition, harassment and limited killing will continue in eight other places in Michigan, including Brevort Lake, Manistique Lake, and South Manistique Lake in Mackinac County, Potagannissing Bay at Drummond Island, Indian Lake in Schoolcraft County, and Long Lake, Grand Lake, and Lake Huron off Rockport in Alpena County. In those places, the U.S. Department of Agriculture Wildlife Services is working with local volunteers to harass cormorants from the water and shoot some of the birds.

Control in the Les Cheneaux Islands, now in its third year, will be a model for other cormorant management projects in the United States. Cormorants are believed to be reducing sport fish populations, especially perch.

This year, agents plan to shoot 50 percent (1,800 birds) of an estimated 2,600 breeding adults. Last year, agents shot 25 percent of the cormorant population, or 1,638 birds out of about 6,550. In 2004, agents removed a little less than 15 percent of the adult population, 954 out of an estimated 6,358 birds.

Five major island breeding colonies in the Les Cheneaux Islands are targeted. Relatively isolated, free from predators, and flush with aquatic food, these islands provide a safe haven for cormorants to nest and raise their young.

Oiling is one of the best ways to kill egg embryos, biologists say. Eggs are coated with corn oil, which suffocates the embryos while tricking parent cormorants into thinking they are incubating viable eggs. If the eggs are simply destroyed, the cormorants will lay new eggs. They lay three to five eggs in a nest, and Pete Butchko of Wildlife Services said cormorants will probably lay a new set of eggs every week if the previous ones are removed from the nests.

Agents plan to oil every egg they find on Les Cheneaux rookeries this summer, which by conservative estimates, could be as many as 5,400 eggs.

Mr. Butchko has described egg oiling as messy work, in which agents fight off birds defending their nests while squirting oil on eggs from backpack sprayers. Last year they oiled 100 percent of the eggs in 2,957 nests, and none of those eggs hatched. In 2004 they destroyed all but 41 eggs in 3,179 nests because they missed one of the nesting colonies.

"I would say there's been some evidence of success," Mr. Butchko said of the cormorant control campaign.

He points to the dwindling number of cormorant nests agents are recording, and two years of Department of Natural Resources reports that yellow perch populations are rebounding.

"Whether that's related to cormorant control or not, I don't know," Mr. Butchko said, though he does believe Wildlife Services control projects are knocking down the local cormorant population.

In 2005, he and other agents heard many reports from local anglers and DNR Creel Clerk Bill Schroeder that "they are catching perch again."

"It's not what you would call definitive success, but it certainly is encouraging," he said.

Islands Wildlife, a Cedarvillebased conservation group, is contributing two volunteers and $500 for fuel toward the harassment effort and a stomach content analysis project. Cormorant stomachs analyzed so far this season show the birds are eating a lot of northern pike. Dave Altmaier of Islands Wildlife said volunteers have found foot-long northern pike inside some of the birds. He also noted that volunteers are "seeing a smaller number of birds compared to what there was out there," a sign, he speculates, that control efforts are working.

Agents are also tracking the movements of cormorants through satellite telemetry. Most cormorants tagged in the Les Cheneaux Islands during the summers migrate to catfish farms in the south. About 65 percent of the nation's catfish are produced for market in farms in the Mississippi Delta region.

Dave Fielder, a state biologist at the Alpena Fisheries Research Station, will continue his research on the perch population in the Les Cheneaux Islands. The state will also continue to monitor fish populations around Beaver Island near Charlevoix, in Saginaw Bay, and in the Bays De Noc. Researchers are keeping an eye on how fish populations respond to cormorant control.

"All the fisheries monitoring is what helps us to make decisions about cormorant management," said Ray Rustem, supervisor of the state Natural Heritage Unit. "The research helps us determine the appropriateness of control actions, and whether action needs to be taken or not."

The Michigan Department of Natural Resources is also cooperating in a survey to identify and count breeding pairs in Michigan. Survey data will be combined with information from other Great Lakes states and Canadian provinces to obtain a full breeding population count of double-crested cormorants on the Great Lakes.

Citizens can report cormorant activity at a new DNR Web site, dnr.state.mi.us/cormorantobs. The department will use this information to identify cormorant migration patterns and locations with large concentrations of birds.