October 13, 2012

Cormorants on Lake Champlain decreasing


---- — PLATTSBURGH — Scientists studying cormorant populations on Lake Champlain have seen a drop in numbers that is approaching an acceptable management level.

For years, anglers and other lake enthusiasts have voiced concerns about a growing number of cormorants on the lake, citing the waterfowl’s negative impacts on fish populations and on the vegetation where the birds breed and raise their young.

The Lake Champlain Basin Program recently released a study that observed management practices for cormorants living on Four Brothers Islands near Willsboro.

“It’s a continuation of work we started on cormorants back in the 1990s,” said David Capan, a retired professor from the University of Vermont who has continued his research beyond retirement.

“Four or five years ago, we were able to develop some coordination amongst agencies across Lake Champlain on how to develop management practices.”


A lot of the focus on cormorant populations was directed toward Four Brothers Islands because that area holds the largest breeding population on the lake by far.

With approval from the islands’ owner, the Adirondack Chapter of Nature Conservancy, Capan spearheaded a plan to oil the eggs of cormorants nesting on the islands. The process prevents the eggs from hatching but influences the adults to continue caring for them without trying to breed again.

“We tried targeting the two islands that were most valuable to other nesting birds,” Capan said, nothing that they have a healthy vegetation cover while the other two are void of growth.

“That didn’t work out as well as we hoped,” he added. “We were oiling heavily on islands A and B, hoping to push the nesting adults to the (two denuded) islands, but after four years of reducing the number of young on those islands, the adults were not moving.”

The egg-oiling project reduced the number of young on islands A and B by 85 to 90 percent, he noted.

“Our conclusion is that because islands A and B have standing trees, the islands are viewed as better habitat to such an extent that they continue to nest there even without success.”


The reduction in offspring has obviously translated into reduced numbers overall, but there was still another section of the cormorant population that had to be accounted for.

“In the past, we’ve operated on the assumption that the Lake Champlain cormorant population was a closed population, that we don’t have a lot of (new) birds coming in or leaving,” Capan explained. “But there is evidence that more birds are coming in during the summer months to feed on Lake Champlain.”

Vermont Fish and Wildlife, in conjunction with the Lake Champlain Fish and Wildlife Management Cooperative, has also been working to reduce the cormorant population through a controlled shooting program.

Birds killed during that program included banded cormorants from Four Brothers Islands as well as unbanded cormorants, and Capan was able to determine that many of those that had been shot did not appear to be “local” but were “passing through” to enjoy the rich populations of alewives and other fish species.

“The Lake Champlain Management Cooperative (which helped establish an acceptable population level for cormorants on the lake) was not as concerned about whether the cormorants were breeding here or just moving through,” he said, noting the bottom line was how many cormorants were on the lake during the summer months.

10,000 BIRDS

The shooting program continued through this summer, and though results have not yet been released, Capan believes those numbers will be down because the cormorant population has decreased.

Over the past several years, more than 10,000 cormorants have been removed from the lake, some through the shooting program and others when the birds and their nests were taken from other areas.

A specific management plan for continued management is still being considered, but Capan believes he will continue his work on Four Brothers Island at least into next summer. 

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SEE THE REPORT To find the Four Brothers Islands cormorant-management report online, go to and click on the report beneath the "What's New" column.