As winter starts to grip a remote Michigan island, a struggling pack again finds the wolf at its door.

What is killing the wild gray wolves of Isle Royale?

No one knows for sure. But it seems certain that this is one of the rare ecological crises that can’t really be blamed on man. Nor can he do much to stop it.

Here, on perhaps the most remote patch of American soil anywhere east of the Mississippi River, a mysterious, evolutionary drama is unfolding.

“If the current trends continue, they will all be gone in five to 10 years,” says Rolf Peterson, a wildlife ecologist at Michigan Technological University who has studied the island’s wolf population since 1970. “And what is so very unique about this is that it’s a natural phenomenon.”

It may not even be the first time the wolves have died out here, speculated Bruce Weber, a spokesman for the National Park Service on the island. “This all could have happened before, hundreds of years ago,” he said.

Miles From Mainland

In the far, deep northern waters of Lake Superior, where the cool summer days are already slipping straight into winter, lies Isle Royale, a 210-square-mile, craggy wooded island 56 miles from the shores of Michigan’s Upper Peninsula.

Six hundred miles north of Chicago and Detroit--and a choppy, 4 1/2-hour ferry ride from the mainland--Isle Royale blooms beautifully in the summer, but is open less than half the year and is completely uninhabited during the winter. It’s no wonder that it is one of the least-visited national parks.

It’s been just as hard for animals to make it here since the island was formed by retreating glaciers 10,000 years ago. Only about one-third of the animals found on the surrounding mainland have ventured across to Isle Royale.

Once here, they find themselves cut off from the mainland animal kingdom, making Isle Royale a perfect research laboratory for wildlife biologists who now watch closely as a wild animal comes face to face with extinction.

Peterson’s work on the island under contract with the National Park Service is the longest running study of large animals anywhere in the world. He spends all summer on the island in a rough-hewn log cabin with his family, and then takes seven weeks each winter to make aerial counts of the wolves.

Modern man had not seen any wolves on the island until the frigid winter of 1948-1949, when one pair apparently traveled across a rare “ice bridge” from the Canadian shore.

When they arrived, they found a wolf’s paradise; an island full of moose, their natural prey.

Also Newcomers

The moose were also relative newcomers. They weren’t sighted on the island until 1910, when they apparently swam across from the mainland.

Without any natural predators on the island when they arrived, the moose population had boomed on Isle Royale--peaking at more than 3,000.

After the wolves arrived, the two species lived in a kind of violent balance. The wolves, eventually splitting into two main packs at either end of the island, ate as many moose as they could catch, but there were always plenty that got away.

By 1980, there were 50 wolves on Isle Royale--an all-time high--and the moose found themselves on the decline.

But then over the next two years, the wolf population suddenly came crashing down, plunging to just 14 by 1982.

Today, there are just 11 left, so few that their packs have broken up, and the wolves are now hunting in pairs or on their own. “They are now in a state of constant social flux,” Peterson said.

The moose, meanwhile, have rebounded, and now total about 1,400.

Peterson has only theories about what happened.

One possibility--and the only one for which man may bear some blame--is that a dog virus swept through the population in the early 1980s. At about that same time, the virus was ravaging the domestic dog population in Michigan’s Upper Peninsula. Visitors are not allowed to bring dogs onto the island, but the virus could even have come over accidentally on the feet of campers.

Moose Decline

But Peterson’s other theories have nothing to do with man. One holds that a decline in the moose population in the late 1970s led to a food shortage, and that the wolves will now start to rebound thanks to a more plentiful supply of moose. One wolf pup was born last winter, and another wolf captured in August had apparently just had pups; so it’s still possible that more food will mean more wolves.

The third, and perhaps most intriguing theory is that the wolves have simply become too inbred. DNA tests of the wolves trapped and later released by Peterson show they are all descended, back six or seven generations, from the same female wolf. They may thus be so inbred that they are now becoming infertile.

“I think genetics is a major part of the story,” Peterson said.

There are plenty of wolves on the surrounding mainland, so there is no point in trying to save the Isle Royale wolves, Peterson argues. Instead, he thinks it’s important to let the cycle play out. Then man can learn how to help when it comes time to save other endangered species.

“The lesson here is that if you want to keep an animal, you’ve got to do it before a species gets this small,” he said. “Now, it’s too late to do anything here anyway.”