Island life isn’t for everyone, nor, it seems, for every wolf.
One year into a federal effort to restock the wolf population in Isle Royale National Park in Michigan’s Lake Superior, a pack of eight relocated from a nearby island appears to be thriving, while four of 11 wolves brought from the mainland have died. Another wolf voluntarily departed last winter, returning to Minnesota over an ice bridge.
The U.S. National Park Service (NPS) today released news of the most recent wolf deaths, and the emerging pattern is clear: Wolves relocated as a pack from Canada’s Michipicoten Island Provincial Park have so far been more successful on Isle Royale than wolves brought individually from either mainland Minnesota, Michigan, or Canada’s Ontario province. The Michipicoten wolves’ provenance as a bonded group was likely crucial to the fact they have all survived so far in the new environment, says wildlife ecologist Rolf Peterson from Michigan Technological University in Houghton, who has studied Isle Royale wolves since 1971. “That’s about the only explanation I can think of,” to account for the difference in the wolves’ fates.
Population ecologist Brent Patterson of Trent University in Peterborough, Canada, has been studying the Michipicoten wolves since a breeding pair crossed an ice bridge from mainland Canada to that island in 2014. Their large size, about 50 kilograms, is another important factor in their survival on Isle Royale, he suspects. Before settling on Michipicoten, where they hunted woodland caribou, the wolves had been preying on moose in northern Ontario, so they came equipped to hunt Isle Royale’s moose. At the time they were moved to Isle Royale, the Michipicoten wolves were food stressed and battered, having eliminated the caribou—but the presence of their pack mates and their large physical stature gave them a leg up in getting through the snow to hunt moose again, Patterson says.
The relocated U.S. mainland wolves, in contrast, were not moose hunters and were generally smaller, although they were considered healthy at the times they were moved to Isle Royale. The circumstances of their deaths have all been different. One Minnesota male died of pneumonia shortly after being moved in fall 2018. The body of another male, from Ontario, was retrieved from a bog in April; it was too decomposed to determine a cause of death. In September, two recently relocated females died; one from Michigan had an infection and wound from the leg trap used in her capture. The second, from Minnesota, died from severe trauma after an attack by another wolf or wolves. (Another Minnesota wolf intended for relocation in 2018 died before its move because of “capture stress.”)
NPS expected some wolf deaths, as well as wolf fights, or other random events to take a toll on the relocated animals, but “all the mortalities are surprising,” says NPS wildlife biologist Doug Smith, who directed a similar relocation of wolves to Yellowstone National Park and has worked on Isle Royale but is not involved in the current effort. In Yellowstone, 41 wolves introduced to restore the predators to the park all survived their relocation. Those wolves belonged to three packs, but individual wolves have also been successfully relocated, Smith says. He points out that moving wolves on a large scale to restore predation is still relatively new. “This is an art, not a science.”
Isle Royale researchers have been watching the movements of the new radio-collared wolves—except for the breeding male from Michipicoten, who slipped his collar in July—and consider their social dynamics to still be in flux. The public can investigate which wolves are hanging out together and where with a new online tool.
The last male wolf of the intensely studied island-born population also died this fall. It dropped dead on a hiking trail, where a ranger found its intact, though emaciated, body on 17 October. Eleven years old, it far outlived most wild wolves and was apparently survived by the 9-year-old island-born female that is both its daughter and its half-sibling. The female had been prodding the male along for several years. Pathologists at the United States Geological Survey’s National Wildlife Health Center in Madison noted broken ribs, as well as several puncture wounds they attributed to wolf attack. “It is still a question in my mind what it actually died of,” Peterson says, noting that wolf attacks don’t usually break bones, although moose kicks commonly do. He may get more answers as the frozen corpse arrives this week in Houghton, where he will dissect the body and preserve the skeleton. Other Michigan Tech researchers plan to sequence the wolf’s genome.