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And then there were three. The last remaining wolves on Isle Royale, photographed this past winter, are a pair and a smaller, hunchbacked wolf (last in line) that may be their pup.

And then there were three. The last remaining wolves on Isle Royale, photographed this past winter, are a pair and a smaller, hunchbacked wolf (last in line) that may be their pup.

Rolf Peterson

Inbred wolf population on Isle Royale collapses

Each January, before they fly to snowbound Isle Royale in Lake Superior, ecologists Rolf Peterson and John Vucetich guess how many wolves they’ll spot. This U.S. national park in Michigan is home to the world’s longest running predator-prey study, of wolves and moose. This year, Peterson figured that they’d likely find a mere seven wolves, given complications of inbreeding in the dwindling population. But the island held only three wolves, as the researchers from Michigan Technological University (MTU) in Houghton announced today. “The collapse of the wolves was beyond our expectation,” Peterson says.

The three wolves included a pair, probably the last ​known to have reproduced, plus a notably smaller wolf that might be their pup. The other wolves are presumed to have either died or left the island last year, in a reverse of how carnivores originally came to Isle Royale, when a bitter winter completely froze the channel to the mainland.

But even as the famed predator-prey study on Isle Royale appears to be on its last legs, other researchers may have caught the birth of a similar natural experiment: Across the lake in Canada, three mainland wolves crossed the ice to a smaller island with different prey and seem to have settled in, as population ecologist Brent Patterson of Trent University in Peterborough, Canada, will report at a wildlife meeting next week. “It’ll be very fascinating to watch,” Patterson says.

The wolves on Isle Royale, which once numbered as many as 50, have been mostly isolated for generations, and the population has been overrun with spinal defects likely as a result of the inbreeding. This winter’s small wolf also displayed an abnormally short tail with raccoonlike stripes and a hunched back—possibly dramatic new effects from the lack of genetic diversity. “It [didn’t] look particularly healthy” in February, Vucetich says, and may be dead by now. He and Peterson collected frozen wolf scat and vomit for DNA analyses to identify the trio.

The fate of the island’s other wolves is hard to pin down. One male wore a radio collar and was spotted dead; his carcass will be collected this spring for autopsy. If all the others died, the 70% mortality rate for the year would be the highest in the study’s history, Peterson says. So the wolves may have simply left via the icy corridor to the mainland, seeking unrelated mates. When the channel froze last year (for only the second time in 16 years) scientists learned later that a female identified by her collar crossed to the mainland and was shot.

This year, an ice bridge formed again, when researchers were on the island. So for the first time scientists got a real-time view of how Isle Royale’s wolves arrived. Genetic analyses have revealed after the fact that such immigrations and resulting matings must have happened several times during the study’s 57 years. In February, Vucetich spotted two mainland wolves on the island. One, a female, fortuitously was fitted with a radio collar as part of a study by the Grand Portage, Minnesota, band of Lake Superior Chippewa. The two visitors canvassed the southwest edge of Isle Royale for 5 days and then headed back to the mainland. The radio-collared Minnesota wolf next cruised two nearby small islands, perhaps seeking easier prey than a 400-kg moose. “That’s how [wolves] get information,” Peterson says. “They walk.” Peterson thinks the newcomers were aware of the resident wolves, but that mating would be unlikely given the few residents and the pair bond of two of them.

Roughly 300 kilometers across the lake from Isle Royale, in Canada, a trio of wolves might have found the Goldilocks option in the forests of 184-square-kilometer Michipicoten Island Provincial Park. Three mainland wolves colonized the island via ice a year and half ago, left briefly this past winter, but then returned and probably have bred.

The island’s appeal is obvious. Based on aerial surveys in February, Patterson estimates it holds 250 to 300 “predator-naive” woodland caribou, which are smaller than moose but bigger than deer. Working for the Ontario Ministry of Natural Resources and Forestry, Patterson and his colleagues radio-collared all three Michipicoten wolves in February and are preparing for a potential Isle Royale redux. Patterson intends to describe the plans next week at the Midwest Wolf Stewards meeting in Ashland, Wisconsin. As on Isle Royale, where the carnivores kept the moose population in check and so helped preserve the vegetation, “the wolves are expected to have a profound impact,” Patterson said.  

Back on Isle Royale, it’s no surprise that moose are booming. This year, their numbers swelled by an estimated 200 to about 1250 despite the harsh winter. Wolves are so scarce that their effect on moose has been essentially nil for the past 4 years, during which time the moose population has grown about 22% annually, according to the MTU report released today.

Such burgeoning populations of moose, deer, and elk, and their effects on vegetation, are crucial issues for national park management, officials say. Geneticists, including Philip Hedrick of Arizona State University, Tempe, advocate introducing new breeding pairs of wolves to Isle Royale. “These animals might give the wolf population a new start and the remaining two adults might eventually contribute to this population,” he said. But park officials say they plan to continue their hands-off stance for the moment. An environmental impact analysis on how to manage the wolves, moose, and forest is to launch this spring with a request for public input. For now, Isle Royale’s few wolves roam alone.

Christine Mlot is a science writer based in Madison.