Watching Wolves On a Wild Ride
For 25 winters, researcher Rolf Peterson has tracked the turbulent twists and turns in the lives of Isle Royale's top predators and preys
- Les Line
- Dec 01, 2000
There are always surprises waiting when Rolf Peterson returns to Isle Royale National Park to spend the dead of winter in the company of the world's most famous gray wolves and the moose that are their bread and butter.
For 25 years, Peterson, a wildlife ecologist at Michigan Technological University, has led what is believed to be the longest-running study anywhere of a top predator and its primary prey. The project began in 1958 under the direction of the scientist's late mentor, ecologist Durward Allen of Purdue University. Allen saw Isle Royale, which is located in Lake Superior, as a natural laboratory, effectively isolated from human impact. Here scientists could count wolves and moose and study their interactions over time.
In the project's early years, when nearby states still paid bounties for dead wolves, coyotes, foxes and other carnivores, the researchers' findings were portrayed by wildlife conservationists as magical examples of nature in harmony. Park visitors learned from biologists' lectures how wolves culled the old and infirm from the moose herd and kept the forest from being overbrowsed. And the Isle Royale story, told in popular magazines, played an important role in changing the public's attitude toward Canis lupus.
But in Peterson's time in the early 1980s, the Isle Royale wolf population reached an all-time peak only to soon crash to the point where it appeared to be on its way to extinction. And in the absence of normally heavy wolf predation, the scientist watched the park's moose population explode and devastate its main winter food supply, the island's balsam fir stands. Recent winters have been especially tumultuous, with a catastrophic collapse of moose numbers and with wolf numbers on a roller-coaster ride.
In documenting these events, Peterson and his colleagues have shown that the Isle Royale ecosystem, despite its remoteness, is not totally immune to outside influences. In particular, introduced disease and extreme, short-term weather shifts have had far-reaching impacts on the balance between predator, prey and the environment.
Isle Royale is a 45-mile-long, 9-mile-wide island (with some 100 satellite islands and islets) that lies much closer to Superior's Ontario shore than the great lake's Michigan side. The sparse crowd of 17,000 visitors that arrives by boat during the three-month summer season commonly encounters moose along the wilderness park's trails, but only a dozen or so hikers a year will be lucky enough to see a wolf. "Isle Royale is the safest place in the world for wolves," says Peterson. "They have very little contact with people, and they're terrified of us."
From October to May, the island is uninhabited except for the seven-week period beginning in mid-January when Peterson and a changing cast of field assistants and Park Service personnel are in residence.
Neither moose nor wolves occupied Isle Royale until the last century--at least in historic times. Indian tribes hunted, fished and mined copper there for 4,000 years, but archaeologists have found no moose bones at their campsites. Peterson thinks the big ruminants, which are strong swimmers, first crossed the 20-mile-wide channel from Canada around 1900.
On Isle Royale, moose found a bountiful supply of food, and their numbers exploded. By the 1920s, several thousand were munching away at the vegetation. The island was in state and private hands at the time, and when the noted biologist Adolph Murie arrived in 1929 to do a field study, he discovered that the forest was in desperate shape, and he predicted a disaster. By 1935, the moose population was down to a few hundred starving animals. The herd recovered only because the next summer fire burned 20 percent of the island and created a new forest. But by 1945, five years after Isle Royale became a national park, moose numbers again had grown to the point where winter starvation occurred, prompting calls for control measures either through hunting or by introducing wolves.
Then in the winter of 1949, nature intervened. Bold wolves--probably only a mated pair--made a run over a solid ice bridge between Canada and the island. It was an extraordinary event. "The weather has to be cold and calm enough for the lake to freeze over," explains David Mech, a U.S. Geological Survey biologist who was Durward Allen's first graduate student on the wolf-moose study. "Then you need wolves predisposed to make a long trek over the ice," Mech adds. "The chances of this happening are pretty remote, or Isle Royale would have had wolves before the 1940s."
Those pioneering wolves and their offspring found a well-stocked larder on the 210-square-mile island. Calves and elderly animals are a pack's main prey. "Few moose between the ages of two and eight are killed by wolves," says Peterson. "Prime-age moose are too dangerous to approach. They commonly stand and pugnaciously face the wolves, which take the cue and leave. To my knowledge, no one has ever observed wolves killing a moose that did not run when first confronted by its predators." The front legs of a 900-pound moose are formidable weapons. Peterson once watched an old and blind bull stand its ground against a wolf pack for three days until the hungry canids decided to look elsewhere for a meal.
By the winter of 1960, two years into Allen's study, there were 22 wolves on Isle Royale while the moose count was 575 and climbing. In 1970, researchers found 20 wolves and 1,430 moose. Over the next decade, however, an astonishing buildup of wolves occurred, with five packs (normally there are three) totaling 50 animals hunting the island in the winter of 1980. Meanwhile, the moose population declined, and a pattern had emerged: Predator and prey were cycling in tandem, with the wolves peaking ten years after the moose herd, at a point when there were a lot of aged animals.
But by 1982, that balance was broken. Isle Royale wolf numbers crashed to 14, apparently because of a deadly new disease called canine parvovirus that had ravaged domestic dogs on the mainland and may have reached the island on hikers' boots. And for more than a decade, even after all traces of the virus had disappeared, Peterson watched the population stagger along at a dozen or so animals and grow top-heavy with old wolves that had little success at replacing themselves.
By 1993, just three females survived, and only one of them had ever successfully raised pups. Wildlife biologists who followed the serial drama through Peterson's annual reports expressed fear that inbreeding had caused the isolated population to stagnate, as had happened with cheetahs in Africa.
Peterson demurred, suggesting that food or even bad luck might be the limiting factor. Whatever the reason, the predator-prey relationship was decidedly out of sync by the winter of 1995, when the moose population stood at 2,400 against 15 wolves.
"It was a matter of time until something broke," the scientist says, "and it broke in a big way." Everything turned against the moose at once in the winter of 1996, one of the severest on record. The temperature at the Isle Royale camp plunged to 43 degrees below zero Fahrenheit, the all-time low. Moose struggled through three feet of snow to find what little winter browse was left. The herd was infested with blood-engorging winter ticks that can cause serious hair loss and weaken even a big bull--but do not affect wolves.
Meanwhile, the wolf population had weathered a long crisis without human intervention (which would be counter to Park Service policy) and had climbed back up to 22. There were pups in all three territorial packs for the first time in nine years, and the predators were not hampered by the deep snow. They responded by hunting in larger packs, tripling the number of moose killed per day compared to normal, less snowy years.
After wrapping up his 1996 fieldwork at the end of February, Peterson reported that Isle Royale moose numbers had been cut in half, to 1,200. He described starving moose falling into Lake Superior when they leaned over steep cliffs to reach "the last tidbit" of browse. But the spectacular crash wasn't over. Spring arrived late and heavy mortality continued into June. "The length of winter was costly for calves and older, weaker moose," he says. "But a surprising number of young adults also perished." By the following winter, only 500 moose were left on the island, and the wolves, now numbering 24, were working hard to find food. "There were only a few calves for them to eat," Peterson reported at the time. "They even dug up the carcasses of dead moose and ate their sun-dried hides. I'd never seen that before."
Even so, Peterson expected the wolves to increase by the 1998 winter survey and was stunned to find that high mortality among both adults and pups had cut their number back to 14. "I didn't appreciate the severity of the food-shortage problem," he says today. The good news is that the population quickly bounced back, and the catalyst this time was an unusually hot and dry summer on an island usually swept by cool breezes or hidden in banks of moisture-laden fog.
"Moose don't perspire," Peterson explains, "and hot weather stresses them to the point where they have a hard time putting on enough fat to make it through the coming winter. Their diminished vigor makes them easier prey for wolves." Last winter he counted 850 moose in a herd that is slowly recovering, along with 29 wolves. And he was surprised to discover a realignment of wolf pack territories in response to changes in moose distribution. "Where we used to have three packs dividing the island, now there are only two."
In a few weeks, Peterson will be back in the air over wintery Isle Royale, flying at 500 feet for close-up views--through a 12-power, gyro-stabilized lens--of animals long accustomed to the ski plane's presence. He's reluctant to predict what he will find this time since "I'm usually wrong." But he adds that unless moose numbers are kept depressed for another decade, balsam fir will be a memory on the southwestern half of the island, where there is good soil and strong competition for growing space from northern hardwood trees.
Asked if he thought about passing the Isle Royale research torch to one of his graduate students, as Durward Allen did, the 51-year-old ecologist replies: "Not just yet. This is the last thing I would choose to give up. Friends tell me I'll probably die out there."
Lobbying on behalf of the Michigan Audubon Society, a young Les Line helped persuade the state legislature to end a 120-year-old bounty on mainland wolves in Michigan in 1960. The National Wildlife field editor now lives in upstate New York.
NWF PRIORITY
Will Wolves Roam Again in the Northern Forest?
When English colonists first stepped ashore in North America, gray, or timber, wolves (Canis lupus) ranged across all of the future 48 contiguous states except for the southeastern coastal plain, which was the domain of the smaller red wolf (Canis rufus). By 1914, the North Woods of Minnesota, Wisconsin and Michigan was the only place where wolves could be found east of the Great Plains--and the U.S. government was about to launch a relentless war of extermination of predators in the West. Sixty years later, when the wolf was added to the federal Endangered Species List, the Minnesota wilderness and Isle Royale in Lake Superior were the animal's last strongholds south of the Canadian border, although packs were occasionally seen in Montana's Glacier National Park.
More recently, however, the wolf's fortunes have changed along with public attitude toward a once-reviled predator. Minnesota wolf numbers have boomed to more than 2,500; wolves have reoccupied northern Wisconsin and Michigan's Upper Peninsula in substantial numbers; and last summer, the U.S. Fish and Wildlife Service proposed downgrading the status of wolf populations in several states from endangered to threatened. Meanwhile, wolves have been successfully reintroduced into Yellowstone National Park in Wyoming and the Bitterroot Mountains of Idaho, and there is a healthy natural population in the Glacier park area.
Now, wolf advocates have turned their attention to the Northern Forest of Maine, New Hampshire, Vermont and New York. Recent studies suggest that this 26-million-acre region, which lacks a top predator in its wildlife community, could support more than 1,200 wolves. "Prey species such as moose, deer and beaver are abundant," says Peggy Struhsacker of NWF's Northeast Natural Resource Center in Vermont. "Restoring wolves would help bring stability to an ecosystem that has been out of balance for more than a century."
But don't expect to hear the howl of wolves in the Northeast anytime soon, Struhsacker adds. Natural recolonization by animals from Canada is unlikely, according to a report by the Wildlife Conservation Society (WCS) in New York. There are formidable barriers to migration such as the St. Lawrence River and highways. And while corridors of natural habitat exist, wolves are heavily hunted and trapped in neighboring Quebec, lessening the likelihood that any animals would be pressured to move across the border.
Yellowstone-style wolf reintroductions are the best strategy for restoring this missing link to the Northern Forest ecosystem, the WCS study concluded, and the Fish and Wildlife Service is developing a recovery plan for wolves in the Northeast. But that process will take as long as five years to complete and is certain to lead to a political minefield. Eighty-five percent of the land in the region is in private hands; the New Hampshire legislature has passed a law prohibiting wolf releases; similar bills have emerged in Maine and Vermont; and many private landowners in New York's Adirondack Park are vociferously anti-wolf.
Struhsacker counsels patience. "It took at least 25 years to bring wolves back to Yellowstone," she points out.
--Les Line
