ISLE ROYALE, Mich. — For 40 years the wolves isolated on Isle Royale have walked on the wild side and prospered. Left alone by man, except for long-range observation, they demonstrated special breeding and hunting habits necessary to survive in a state of nature.
Now the wolves are dying off, and the question is what role nature has played in their decline. The answer may help determine how vulnerable isolated groups of animals are to genetic weakness and whether the Isle Royale community can be saved.
The first Eastern Timber wolves arrived on this north-woods island in the winter of 1948, crossing icy Lake Superior from Canada. A single, pregnant wolf may have led the way, or a pack of as few as two wolves. But within a brief time, they began to multiply under the protective watch of the National Park Service, which resolved to maintain a habitat for the wolves free of human intervention. There had been no radio collars, no trapping and no medical probing of wolves here.
By 1980, the population had grown to 50 wolves in three distinct, territorial packs, and scientists who monitored them from an airplane every winter marveled at their behavior.
Much of humanity's knowledge of wolves comes from those observations: their patient probing of moose 10 times their size, striking only if the moose runs; their inability to conquer younger moose, and their practice of permitting only the strongest wolves to breed while mobilizing the entire pack to raise the pups.
Isle Royale wolves are "often brought up (in conversation) as to how good things work if we just leave them alone," said Rolf O. Peterson, a wildlife biologist who has studied them since 1970.
Even when the population dropped to 14 wolves in 1982, Peterson and his colleagues were not alarmed. Moose were said to be undergoing a generational change, the majority being young and strong enough to evade their carnivorous predators. Peterson predicted that the wolf population would rebound and stabilize at 24 once the moose aged, and part of his prediction came true. In 1984, the population increased to 24 wolves.
But instead of stabilizing, the community declined again, dropping to 12 wolves last winter. Peterson expects as few as seven this winter. Only the East pack and West pack remain. The Harvey Lake pack dispersed after its leader, full of moose, was killed in a surprise attack by the East pack last January.
"I'm accustomed to seeing lots of wolves, lots of tracks," said Peterson, who teaches wildlife ecology at Michigan Technological University. "There's a lot of empty space out there now. A death watch."
Unable to blame the decline solely on food supply, experts are focusing on two possible problems--one internal among the Isle Royale wolf packs, the other external.
The first explanation is that the population is so small, isolated and inbred that it has lost genetic variability, preventing the wolves from fighting disease or adapting to an ever-changing environment.
Scientists believe that genetic testing of the wolves will help forecast the fate of other isolated wild animals--including the Chinese panda, Florida eastern panther and Yellowstone grizzly bear--that have been driven from their natural habitats.
The second theory suggests that a virus introduced by dogs is the source of the decline. This theory is a direct result of a Park Service decision last spring to end its nonintervention policy. Four wolves were trapped, tranquilized and thoroughly examined. The blood of two of them contained antibodies to canine parvovirus, a fatal disease of young domestic dogs that prevents food absorption.
Although domestic dogs have been prohibited in Isle Royale since the mid-1970s, park rangers who run the island find a handful each year brought in by boaters. The disease is transmitted by feces.
The buildup of antibodies in the wolves indicates that they were exposed to animals with parvovirus, said Bob Krumenaker, Isle Royale's resource manager. It is possible that wolf pups unable to absorb their mothers' milk have died. "We don't know what effect it's had," he said. "It could be severe and caused the (population) decrease, or it could've been a mild exposure and they fought it off."
Peterson said no single factor, but a combination of disease, genetics and food shortages--a vast majority of moose are still young enough to stave off attack--may account for the deaths.
The four trapped wolves were fitted for radio collars so they could be followed from the air. The collars have what is called a "mortality sensor," which beeps rapidly when an animal has stopped moving for four hours. The plan is to retrieve dead wolves and perform autopsies to determine the cause of death.
Peterson proposed radio collars 14 years ago to monitor the impact on wolves of changes in the trails and campsites of the island. Had he prevailed, more would be known about the disease. But he was rebuffed by Park Service purists.