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A suggested cull of double-crested cormorants has sparked fierce debate, highlighting a conservation dilemma posed by the recovery of a bird that was once driven almost to extinction by contaminants and human persecution.

The province's biggest concentration of the birds is in a Toronto park. But the focus of the debate over whether to kill cormorants is Canada's southernmost piece of land: Middle Island in Lake Erie.

Parks Canada says a unique mix of trees and plants on Middle Island won't survive if cormorant populations aren't brought down from around 6,000 to 1,500.

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"Our mandate for the island is to maintain and protect the rare Carolinian ecosystem," parks superintendent Marian Stranak said. "We're faced with a species that for many reasons is creating significant stress."

Ornithologists and animal-protection advocates say Parks Canada's control plans are based on inadequate research and a poor understanding of the cull's long-term effect.

"Yes, they have a mandate to protect ecosystems in their care," said biologist Alan Wormington, a Leamington, Ont., consultant who has worked at Middle Island. "But generally it is to protect them from people or man-induced activities, not from native species that they decide are undesirable."

Mr. Wormington believes he knows the true reason for the cormorant crackdown. "They're ugly and black and they barf up fish," he said, mimicking anti-cormorant feelings.

They also produce nitrogen-rich droppings that kill the trees they nest in, and there's a widely held perception - contradicted by most scientific research - that they have an adverse impact on the Great Lakes sports and commercial fishery.

The controversy arises at a time when nest counts across the Great Lakes indicate that populations are stabilizing - from 115,000 nests in 2000 to 113,000 in 2005. On Middle Island, the count peaked at 6,635 in 2002 and declined to 4,688 this year.

Computer modelling at the University of Alberta sets the forest's carrying capacity at 1,200 cormorants, Tammy Dobbie, ecosystem management co-ordinator at Point Pelee National Park, said.

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In Toronto, where Tommy Thompson Park boasts 7,000 nests, a cull has been ruled out, said Ralph Tonninger, environmental projects supervisor for the Toronto and Region Conservation Authority.

"We celebrate all birds and wildlife that use the site," he said, "and that includes cormorants - they're part of the reason it's such a bird resource." The park, an accidental wilderness also known as the Leslie Street Spit that grew from a pile of rubble, was designated a globally important bird area in 2001.

Mr. Tonninger said the agency is concerned over the loss of about 20 per cent of the tree cover in the park, and is monitoring the cormorants' effect on a colony of black-crowned night herons that is the largest in Canada, at around 1,000 nests.

These herons nest with cormorants, but it's not clear whether eventually the cormorants might take over. Mr. Tonninger said the agency has been looking at whether harassment or oiling eggs, which kills the developing chick, is required, but the underlying philosophy is to provide for natural succession.

Toronto bird artist and author Barry Kent MacKay, a founding member of Cormorant Defenders International, believes Parks Canada should do the same.

"It's such a contrived and expensive and cruel way of saving these plants," he says, noting that most grow throughout their broader range, the northeastern United States, and many used to grow on the Ontario mainland, and could still, if habitat is set aside for them.

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Mr. Wormington and Mr. MacKay favour allowing nature to take its course, even if it means a changed Middle Island ecosystem. That's not an option for James Duncan of the National Conservancy of Canada. He travelled to Cleveland in 1999 and successfully bid for Middle Island when it was put up for auction by its American owners. The island - Canada's southernmost landmass - was then purchased by Parks Canada.

"What we support is the ongoing management of Middle Island for what we bought it for, which is biodiversity conservation," Mr. Duncan said from his London, Ont., office. As for the cormorant issue, "we're looking for Parks Canada to deal with that in order to maintain the island."

DOUBLE-CRESED CORMORANT NESTS ON THE GREAT LAKES

Year Approximate number of nests
1950 900
1962 300
1972 135
1983 2,400
1991 38,000
1997 89,000
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