On a remote island in the Great Lakes, wolves and moose struggle against global warming's effects
By Heidi Ridgley
Candy Peterson stands near a trail thick with fallen birch and fir trees hung in stringy lichen, about a quarter mile in from a boat launch on the shores of Lake Superior. She is tall and lanky, and from this vantage point appears to tower over the tiny fishing cabin she and Rolf, her wolf biologist husband, have called home every summer for decades.
Taking charge of five volunteers about to head off in search of bones from moose that died over the winter, she is playing the role of drill sergeant on this 45-degree June morning. She checks off a list of must-have items before the group traipses off for a week in Michigan’s big north woods.
But some backpacks are too heavy and she needs to sort that out first. "No extra clothes!" she commands firmly—survival in the wilderness is serious business. But the group is also expected to enjoy themselves—and that’s why she is smirking. "Did you take too much food?" Sheepishly, a woman offers: "I have some art supplies." "Ah!" Peterson teases, "Now the confessions come out!"
Since 1970, the Petersons have been collecting moose bones on Isle Royale, a remote, carless, 45-mile-long island about 56 nautical miles off Michigan’s Upper Peninsula and the least-visited national park in the country. Most coveted is the metatarsal, the last of the three bones in a moose’s rear leg. It reflects early nutrition and speaks volumes about the state of the ecosystem the year the moose was born. This is important information given the direct impact moose health has on the island’s wolf population, which is the true subject of the Petersons’ research.
"These wolves are on the edge of a serious downturn," says Rolf Peterson, co-director of the wolf program at Michigan Technological University, sitting beside the cabin’s crackling woodburning stove after sending the volunteers on their way. "I can’t see anything else."
The problem for wolves is that in recent years their main prey—moose—has been suffering from unseasonably high summer temperatures on the island. "We’ve had shorter winters now almost every year since 1998," says Peterson. "I’ve measured it myself." He points to northwestern Minnesota as an example of how rising temperature can wipe out moose. There, prairie and scattered trees do not provide enough shade to offset global warming, and moose numbers have dropped from several thousand to 100 in recent years.
When it’s too hot, moose, which thrive in frigid climates, won’t forage. "Moose don’t perspire," says Peterson. "They don’t pant. Their only response to hot temperatures is to breathe faster." This draws air past membranes in their long nose to their lungs and causes cooling through evaporation. Many older moose—the mainstay of wolves—die from heat stress. The survivors will cope by spending a majority of their time in cooling waters instead of feeding. Come winter, they won’t have built up enough fat reserves.
"They’ll try to survive by eating tree lichens," says Peterson. "But that is like eating dust." Many will starve or become easy pickings for their only predator, which at first glance would appear to be a boon for wolves. But if moose don’t survive to give birth to calves each spring, replenishing the population, in subsequent years the wolves will go hungry themselves and suffer their own population crash. This is what worries Peterson.
Wolves first claimed Isle Royale in the late 1940s, when at least two loped across a 15- to 20-mile ice bridge from Ontario, Canada, during a particularly cold winter. There they found a cornucopia of moose, no competition from other predators, no cars and few humans. The moose themselves descended from those that swam over at the turn of the last century.
Peterson’s research carries on work pioneered by Durward Allen in 1958, making this project the longest uninterrupted study of a predator and its prey in the world, according to Michigan Technological University. The small size of the island and its isolation has made it an ideal natural laboratory in which to count wolves and moose and to study their interactions over a long period of time.
"Wolf-moose research on Isle Royale has kind of set the standard for the rest of us studying wolf-prey systems," says Doug Smith, leader of the wolf project in Yellowstone National Park. "I mean 80 percent of wildlife research lasts three years or less and the Isle Royale team is working on their 51st year. The benefits of long-term research are tremendous and what they have done to tease out the complexity of the story is an example and inspiration to us all studying such things."
Since its arrival, the wolf population has gone from a high of 50 in 1980 to 14 in 1982 after canine parvovirus struck the island, falling to a low of 12 by 1988. The deadly disease was later traced to a Chicago dog brought to the island illegally over the 4th of July. (Dogs are banned here to prevent passing this common canine disease to wolves.
With wolves nearly wiped out, moose numbers skyrocketed to around 2,400 during the next decade—a level not seen on the island since the arrival of the wolf. Then their population crashed in 1996 from starvation. "Half the bones we find today are from moose that died in 1996," says Peterson. "Prior to that moose were cranking out hundreds of calves every year." The calves that managed to live are the aged moose the wolves are feeding on today. "But they are old and won’t live much longer," he adds. "So there’s not much out there for the wolves to eat right now. Add warming temperatures to the equation and wolves are being hit with a double whammy." The heat could also cause an explosion of blood-sucking, anemia-causing ticks, further compromising moose and—by extension—the wolf’s existence on Isle Royale. "Nobody knows yet how parasites will respond to temperature change," says Peterson.
This year’s winter wolf count, done via airplane in March by Rolf Peterson and co-director John Vucetich, pinpointed 24 wolves in four packs. "We might miss one occasionally," says Peterson. "But wolves come in big groups with exclusive territories. There aren’t many places you can get an accurate count of a wild population—but you can here on an island where they’re stuck with lots of snow."
They also counted 530 moose. The numbers are low for both, but for wolves, they could easily become dangerously low. "Wolves are always just hanging on," says Peterson. To make matters worse, this spring the alpha female of the island’s eastern pack died giving birth to eight pups. None of the pups survived, and now only the alpha male is left, which makes Peterson wonder if the pack will last past autumn.
Later that afternoon, we head out to the island’s Tobin Harbor, about 10 miles from the cabin, to search for the last dead moose of the winter—the one that fed the ill-fated female and her eight doomed pups. "I never get tired of looking at wolf kills," says Peterson as he starts up the boat’s motor.
Along the way we pick up Vucetich and his wife, Leah, also a biologist. Vucetich spotted the moose kill site from a plane in February. "I saw the two East Pack wolves bedded on top of the ridge one day," he tells me. "I thought nothing of it. Then two days later, flying, I saw moose and wolf tracks everywhere."
Once the boat grounds on shore and the GPS (global positioning system) coordinates are locked and loaded, we fan out off-trail watching the ground for protruding bones. We plow through the thick balsam fir, sometimes sliding down in slow, unexpected, giant steps when the rotting, fallen birch logs give way beneath our feet.
"Keep the sun at 2:30," Rolf Peterson instructs just as his wife calls out she’s found an upper tooth row and part of a skull. I find a humerus bone. Leah finds a jaw bone but none of them are from the moose killed last February. They are all too old.
Finally, we find what remains of the East Pack female’s last winter meal. It looks like a giant moose-hair-filled pillow exploded all over the ground. Nearby, what’s left of the stomach resembles a pile of darkly stained sawdust. "The wolves won’t touch that," says John.
"From the skull, I can tell it’s an old cow," says Rolf, documenting the find, as he has all the others today, in a small notebook. "She had bad teeth and arthritis. Her teeth were bad enough to affect her health."
With the metatarsals, skulls and jawbones of all five finds packed in plastic, stuffed in backpacks and cradled in arms, we head toward the boat. We only get about 10 feet before Candy calls out, "Oh, did you see the antler over here, Rolf." "Oh, geez," sighs Rolf, dropping his load to pull out his notebook. "This must be some kind of record," he adds. "We’ve found six in three hours—in 1/10 of a square mile. It’ll probably be more than the volunteers will get all week." This time, tromping back to the boat, Candy is told she cannot look down.
When they drop me off at the main harbor on their way back to their fishing cabin, I realize I am still in the territory of the eastern pack, now just a solitary male with no mate and an uncertain fate. Whether climate change will throw all the island’s wolves the ultimate curve ball remains to be seen. "If wolves don’t make it here, there needs to be a debate about what to do," says Rolf. "Was their disappearance natural or not? The arrival of parvo wasn’t. Climate change is human-caused so we would hope that we could talk about wolf reintroductions if that is what wipes them off the island."
In the meantime, Rolf and the rest of the team watch the wolves and wait. Wolves claimed this remote island on their own and then refused to blink out even when the odds turned against them. Beating the odds is something that wolves are accustomed to, and their tenacity fills Peterson with hope for their future.
Senior editor Heidi Ridgley makes no bones about it: Searching for moose remains is hard work.
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