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Cormorant Reduction Planned: Birds Effect on Ecosystem Cited

January 24, 2008

MADISON — Double-crested cormorant populations on Green Bay and Lake Michigan in northeastern Wisconsin are expected to fall in the coming years.

The Natural Resources Board approved plans on Wednesday targeting the large, fish-eating bird that would cut the number of cormorant nests by about one-half on islands on Green Bay and Lake Michigan.

About 90% of the state’s breeding population lives in these waters.

Cormorant numbers have sharply rebounded since they were almost wiped out in the 1970s. Their growth is attributed to the ban on DDT, healthy fish stocks in Wisconsin and in fish farms on the southern Mississippi River where the birds winter.

Cormorants have been blamed for harming fish populations and destroying vegetative habitat on unpopulated islands where the vast majority of Wisconsin cormorants live. The acidic nature of cormorant feces has denuded some forested islands on Green Bay.

But the birds’ effect on fish stocks may be unfounded: Field studies in 2004, 2005 and 2006 by the University of Wisconsin-Madison concluded that cormorants did not affect yellow perch populations, a key sport fish in Lake Michigan waters.

Advocates of the birds, including a representative of the Madison Audubon Society, said at Wednesday’s meeting that it isn’t clear if cormorants are having a destructive effect on the ecosystem. The once-forested islands, for example, might now provide homes to ground-nesting birds.

Nevertheless, lawmakers have pushed for more action, and with cormorant populations growing, Department of Natural Resources officials recommended the management plan.

Under the plan, the number of cormorant nests would be reduced from an estimated 10,000 to 5,000 on four distinct colonies in northern Door County and from 2,400 to 1,000 on Cat Island in lower Green Bay.

There are no plans to reduce cormorant populations elsewhere in Wisconsin, such as the Mississippi River, Lake Superior and Lake Winnebago. There are no known resident cormorant populations on lakes in metro Milwaukee.

Jeff Pritzl, a wildlife biologist for the DNR, said the agency will reduce populations by coating nests with corn oil, which prevents hatching.

He said there are no plans to shoot cormorants at existing locations — a practice used in Michigan and Ohio.

But Pritzl said the agency might use lethal means to remove cormorants that move into new areas of Wisconsin.




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