Climate Change Is Burning a Wolf Pack’s Last Bridge to Survival
For the gray wolves of Michigan’s Isle Royale National Park, climate change has turned their island home from a refuge of solitude into untenable isolation. From a population of 50 at its height, the number of wolves has dropped to fewer than nine on the 206-square-mile enclave today.
Soon the island population could go extinct, thanks to a warming world.
Isle Royale rises out of the northwest corner of Lake Superior, about 11 miles from Canada’s coastline. For its size, the island is thick with forest and teems with wildlife, especially moose.
Wolves were first spotted on Isle Royale in 1948; they were likely attracted by the moose. But how did either species get out there in the first place?
By way of ice bridges from the mainland to the island, said wildlife ecologist Rolf Peterson of Michigan Technological University. But continued burning of fossil fuels has warmed winter temperatures in the region. Ice formation on Lake Superior has decreased, and ice bridges are becoming increasingly rare.
“In the ’60s, an ice bridge would form about four out of every five years; now, it’s more like one out of every 10 years,” Peterson said.
But during a February cold spell that nearly paved the Great Lakes in ice, two wolves made the trek from their home range in Minnesota’s Grand Portage Indian Reservation to Isle Royale. The pair were a young male and a female with a radio collar that allowed researchers to monitor their travels.
Experts hoped that romance would blossom between the locals and the tourists during their five-day stay. But they saw no signs of mating before the pair crossed back to the mainland.
Peterson knows firsthand how critical ice bridges are to the survival of the Isle Royale wolves. In 1997, he observed how one male wolf that made the crossing affected the genetic health of the island pack. “He revitalized the wolf population,” Peterson said, “but now, 15 years later, all of the wolves on the island are descendants of his.” Generations of inbreeding have left the wolves susceptible to disease, heart abnormalities, and low sperm counts in males.
From an average of 25 individuals over the past several decades, only nine wolves were spotted in 2014. Peterson will not be releasing this winter’s head count until the end of the month, but he admitted that, to his dismay, the number was fewer than nine.
“There’s no scientific doubt,” Peterson said. “The problem is genetic isolation, and if something isn’t done soon, the existing population will cease to exist.”
Nearly free of predators, the moose on the island have nearly doubled in number, from 500 in 2007 to more than 1,000 in 2014. That’s bad news for their favorite forage, the island’s balsam fir trees.
“Moose are at extremely high-density levels on the island, and when they’re not kept in check, they can decimate the forest vegetation and their own food supply,” Peterson said. Without wolves to thin the population, moose eat as much vegetation as they can. Once that supply is gone, they starve.
It’s a cycle Peterson recognizes from reports on moose populations prior to the 1948 wolf crossing.
After watching wolf numbers decline over the past decade, officials at the National Park Service announced last spring that they would look into introducing outside wolves to the island as a way to increase genetic diversity. But the agency has not yet reached a final determination.
“This issue is bigger than only wolf genetics,” Isle Royale superintendent Phyllis Green said in a statement. “We are charged with a larger stewardship picture that considers all factors.”
But Peterson, who has been advocating for a wolf introduction program similar to the program at Yellowstone National Park, doesn’t think there’s time to go through the usual decision-making process, particularly an environmental analysis that could take years to complete.
“The headlines are going to read, ‘They’ve studied the wolves to their death,’ ” he said.