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Thirty years ago, the cormorant was a poster bird for the campaign to clean up DDT, the pesticide killing creatures here and abroad. The Great Lakes, home to 900 nesting pairs in the early 1950s, had a mere 125 by 1973, with scientists unable to find even a single pair on Lake Michigan or Lake Superior.

Photos showing chicks born with crossed beaks and unable to feed led to public outrage and a reduction in use of the chemical, giving the bird a chance to bounce back.

And bounce back it has. Today, the cormorant is more numerous on the Great Lakes than at any time in recorded history.

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Now the "crow ducks" are so common that some of them have been condemned to death - a bizarre state of affairs for a species that was so recently in peril.

In fact, says Mark Ridgway, a biologist with the Ontario Ministry of Natural Resources, it's the first time in Canada "we've gone from having an organism that's a rarity to having a management issue. No one's confronted this before."

The cormorant is one of a growing number of cases in which human intervention, however well-meaning, has had unintended consequences.

From elephants in South Africa to alligators in Florida and even the newly reintroduced plains bison in Saskatchewan, wildlife managers accustomed to dealing with endangered species are started to confront some that have become "hyper-abundant." Animals once in grave danger have become a threat to others.

So what is a responsible conservationist to do - let nature run its course and hope for the best or, to paraphrase George Orwell, kill the cormorants because some lives are more sacred than others?

'a dying island'

The stench of guano from the 20,000 cormorants on Lake Erie's tiny Middle Island is overwhelming - and the visual impact is equally dramatic. More than 40 per cent of the forest canopy is gone, stripped for nests, and the birds' droppings have altered the chemistry of the soil.

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But the real problem, conservationists say, goes beyond aesthetics. The 18.5-hectare island in Point Pelee National Park is part of Canada's rare Carolinian ecosystem and home to nine species protected by federal legislation, including the eastern fox snake and the red mulberry tree.

So many cormorants in such a small space amounts to a death sentence for these species. "This is a dying island that supports a dying population of plants and animals," says Marian Stranak, the park superintendent.

Reducing DDT helped, but the cormorant truly took flight when humans unwittingly supplied them with a never-ending banquet in the form of invasive alewife fish in the Great Lakes and farmed catfish in the bird's U.S. wintering grounds. By 1993, the big greenish-black water birds had increased nearly 300-fold to 38,000 nesting pairs. Now, many fishermen say they are directly to blame for a decline in valuable fish stocks.

A drastic solution is being adopted. Between 2003 and 2006, cormorants were culled at Presqu'ile Provincial Park on Lake Ontario, in a bid to rehabilitate its woodlands for such species as herons, egrets and monarch butterflies.

Now, Parks Canada is following suit on Middle Island. The federal agency is two years into a five-year plan to shoot about 80 per cent of the island's nesting pairs, hoping the ecosystem will rebound.

Parks Canada's chief ecosystem scientist, Stephen Wood-ley, insists that anything less than a cull would be irresponsible. "If we're going to protect ecological value, we have to intervene in nature far more frequently than we ever thought we would have to."

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It's because humans have dramatically changed the ecosystem, he and others argue, that many systems must be managed, perhaps in perpetuity. "Nobody likes to kill animals," Mr. Woodley says, "but I think there is a pretty good understanding now that in certain cases we do have to cull animals for the greater good of ecosystem health."

That's the conclusion South Africa came to last year when deciding to cull the elephant, an animal endangered in much of the rest of the continent. After a 14-year moratorium on hunting, the elephant population of Kruger National Park had roughly doubled to 14,000, park spokesman William Mabasa says.

Transporting elephants to other countries is prohibitively expensive, but South Africa has little suitable habitat left.

The cull has yet to begin, but retired Kruger elephant specialist Ian Whyte says it's for the best. "Elephants have big appetites," he told a local newspaper. "You can utilize an area to maintain biodiversity, or else you have a purely elephant sanctuary. You can't have both."

HUNTS HUMANS

Florida faced a different dilemma. In the late 1960s, the alligator was in big trouble but then anti-hunting laws were enacted and some wetlands rehabilitated. By the late 1980s, the reptile had recovered, and now is a danger to humans - an average of 12 fatal attacks a year in the past decade.

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Letting nature take its course is simply not an option. "Humans take precedence over alligators," says Allan Wood-

ward, a biologist with the Florida Fish and Wildlife Conservation Commission.

As for the plains bison, it was recently reintroduced to Grasslands National Park in Saskatchewan after an absence of 120 years, but Parks Canada already has a plan to keep the number at a sustainable 300.

"The area can only support so many animals," Mr. Wood- ley says. "If there are more, they start to wreck the range and you start to eliminate species from the ecosystem. They will graze the grass down to dirt and there is actually nothing growing."

The 130 bison in Grasslands are expected to reach 300 within a few years. While the preference is to move them, Mr. Woodley says, with so little suitable habitat left, a lethal cull is entirely possible.

But back at Middle Island, the cormorant's fate has already been decided. Gunshots will ring out every spring until 2012, when wildlife managers hope that the lives of the island's other inhabitants no longer hang in the balance.

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Sharon Oosthoek is a Toronto-based writer who specializes in science and the environment.

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