HOUGHTON, MI--The wolves of Isle Royale National Park have surprised scientists again by staging a dramatic comeback just when wildlife managers were worried that the island park's most storied species might be headed for trouble.
Several times during the past two decades biologists have felt that canine parvovirus or a perceived genetic weakness resulting from inbreeding was placing the wolves' survival in grave jeopardy. And when last winter's survey turned up only 14 wolves in the park, those concerns increased.
But what a difference a year makes!
Park Superintendent Douglas Barnard announced today that this winter's survey showed the island's wolves had boosted their numbers to 25. "That's the most wolves we've had in the park since 1981 and the biggest annual increase ever," he said. Barnard said the increase was due primarily to high reproductive success by two of the island's three wolf packs.
"Two of the packs produced six pups apiece," he said. "One pack comprised of only a male and female didn't have any pups survive, and there are three single wolves wandering around out there without any pack affiliation."
Michigan Tech's Dr. Rolf Peterson, who conducts the annual winter wolf-moose census for the National Park Service, points to two main causes for the wolves' reproductive success this year.
"The park's moose have been generally in poor condition due to a heavy winter tick infestation caused by the mild winter and early spring of a year ago," he says. "The unusual heat of the summer also made it difficult for them to put on the fat required to survive through the winter." Peterson says the resulting diminished vigor made moose easier prey for wolves.
"Secondly, there are lots of moose calves now, and an increasing number of adults who are reaching old age. Both make easy prey for wolves," he explains.
Peterson says the park's East and Middle packs each produced six pups during the past year, so that these packs now number 10 wolves apiece. "We believe the West pack produced three offspring, but none of them survived," he says. "We don't know why for sure, but it may well have to do with the scarcity of moose at that end of the island." He says the park's moose population numbers 750 this year, as compared to 700 a year ago, with most of the animals concentrated in the east and middle portions of the island.
Peterson is encouraged by the fact that dead wolves found by the survey crew during the past few years have been disease-free and showed no direct signs of any genetic problem that biologists thought might have caused poor reproduction in past years. In the past year only one wolf has died on Isle Royale, and biologists determined that it had been killed in a territorial dispute by other wolves.
National Park officials are hoping for continued positive growth in the wolf population that would keep the total number of wolves on Isle Royale in the high 20s during the next several years.
Wolf research on Isle Royale is funded by the National Park Service, National Science Foundation, and Earthwatch.
Materials provided by Michigan Technological University. Note: Content may be edited for style and length.
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