Major Wolf Die-Off Recorded On Isle Royale

March 05, 1998

HOUGHTON, MI--Officials at Isle Royale National Park reported today that more than half of the timber wolves present on the Lake Superior island park last year have died. Park Superintendent Douglas Barnard said that 13 of the 24 wolves seen in the park during a survey held during the winter of 1997 have since succumbed. He said it was one of the steepest declines recorded since wolves first migrated to the island during the winter of 1947-48.

"We had anticipated a modest increase in wolf numbers this year," said Barnard. "Mother Nature is unpredictable."

Barnard said this winter's survey showed 14 wolves in the park, including three pups born since the completion of the 1997 survey. Biologists aren't certain what caused the decline, but suspect it may be tied to a sharp drop in the available food supply, since the island's moose population suffered a major die-off in 1996 due to a severe winter and a very late spring. Many of those animals were older moose that normally provide the main food source for wolves.

"This year's wolf decline could just be an aftershock of the moose die-off in the spring of '96 when we lost nearly 2,000 animals--almost 80 percent of the herd," said Dr. Rolf Peterson, a wildlife biologist at Michigan Tech University who heads the park's annual wolf-moose study. "Many of the animals that died then were old and weak--the kind wolves love to prey on. Those animals are no longer available, so wolves have had to rely on calves they could kill, since healthy adult moose are quite able to defend themselves against attack under most circumstances."

Peterson said Isle Royale's moose herd is up to about 700 this year, an increase of almost 200 from the 500 animals recorded last year. He said the island's moose are in good shape because competition for food is not nearly so fierce as it was when the herd numbered 2,500.

"One thing that has happened is that we've moved to a completely new generation of wolves," he said. "All of the wolves in the park now are less than five years old. Their reproductive performance will be of great interest, since they are even more in-bred than their parents."

Peterson said there were 10 wolf pups alive on the island last summer and only three have survived to this winter. That leads biologists to wonder if perhaps canine parvovirus is again present in the population. "We plan to live-capture some of the wolves this spring and take some blood samples to see if that's the case," said Peterson.

Major funding for the Isle Royale study is provided by the National Park Service, the National Science Foundation, and Earthwatch.
For more information, contact Dr. Rolf Peterson at 906-487-2179 or e-mail:

Michigan Technological University

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