Michigan Tech
Wolves Decline; Moose Increase in Annual Isle Royale Study

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HOUGHTON MI -- The lack of winter weather explains many of the changes in the annual wolf-moose survey at Isle Royale National Park, according to Michigan Technological University's Rolf Peterson.

Peterson, a professor of wildlife ecology at Michigan Tech, said the 2002 survey counted 17 wolves on the island, as opposed to 19 last year. The island's moose population increased from about 900 last year to 1,100 in 2002.

"The significant factor was a lack of winter," Peterson said, referring to the very light snowfall this year. "Moose were in places where we don't normally see them in the winter--on hillsides and out of the conifer swamps."

The Isle Royale wolf-moose survey is the longest running predator-prey study in the world, now in its 44th year. Peterson has conducted the study for the last 32 years. As an island in the middle of Lake Superior, Isle Royale presents a unique opportunity for such research.

Peterson said the wolves suffered a mortality rate of almost 50 percent this winter and that last year's seven pups kept the population near steady. The Isle Royale wolves have formed three packs: the east pack with six members, the Chippewa Harbor pack with five, and the middle pack with four. There are also two single wolves unattached to a pack.

Researchers confirmed a confrontation between the east pack and the Chippewa Harbor pack, with the east pack's alpha male killed. Peterson's team found that particular wolf, one of four on the island wearing a radio collar; just offshore in Lake Superior.

"The Chippewa Harbor pack has been pushing the east pack aside and enlarging their territory," Peterson said. "A mild winter is always tough on the wolves and this probably contributed to the confrontation.

"We watched about 15 encounters between wolves and moose this winter," he said. "The moose were almost always intimidating, so the wolves didn't bother to attack."

Typically the wolves prey on old moose and young calves. But with little snow cover, the moose could move more freely and avoid the wolves. "Last year, two-thirds of the kills were moose calves," Peterson said. "This year, it was about 20 percent. The wolves had to work hard to find a moose to kill."

Peterson also said that all three packs had breeding activity, so he expects three litters of pups to be born in late April.

While the moose have fared relatively well this winter, Peterson says they could begin to have problems this spring and summer.

"The trend of warmer temperatures, and a warm, dry spring, could mean an increase in tick infestation of moose," he said. High winds in December also caused a large blow-down of the balsam firs on the western half of the island. The moose prefer these for food.

"We lost 16 percent of the fir trees on the western half this winter," he said. "In the last 13 years, about three-quarters of these trees have disappeared. Younger trees can't grown because the moose are eating them. While I expect the moose to increase over the summer, there are some big uncertainties ahead."

The wolf-moose study is supported by Isle Royale National Park, the National Science Foundation, the Earthwatch Institute, and a number of individual donors.