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Ticks Reduce Isle Royale Moose Population
For more information on this story contact:
Email:Dean Woodbeck

A tick infestation accounts for 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 2003 survey counted 19 wolves on the island, as opposed to 17 last year. The island's moose population decreased from about 1,100 last year to 900 in 2003.

"Winter ticks will slow the moose down for a couple of years,” Peterson said. "The tick infestation resulted from an early, warm spring in 2001 and an unusually mild autumn that year. This was an event that affected moose herds from New Hampshire to Alberta since 2002. It has killed a lot of moose in the region.”

The Isle Royale wolf-moose survey is the longest running predator-prey study in the world, now in its 45th year. Peterson has conducted the study for the last 33 years. As an island in the middle of Lake Superior, Isle Royale presents a unique opportunity for such research.

“Our objective is to understand how the moose and wolves interact when humans are not affecting the outcome,” he said.

Peterson said there is a lag time before the moose feel the effects of the tick infestation. The ticks attach themselves to the moose in the fall and are on the moose all winter.

“The biggest effects are in late winter as female ticks withdraw blood to support their own reproduction in the spring, when they drop off the moose,” Peterson said.

Weather continues to play a role in another way. Isle Royale “had as long a stretch of cold as I’ve ever seen,” Peterson said. “Plus, there was no snow at all when we got there in early January.” In the two months he spent on the island, he reports a snow depth of no more than 10 inches.

The lack of snow benefits the moose, because they can freely roam the island. A larger snowfall causes the moose to hunker down in conifer swamps, making them easier prey for the wolves. Typically the wolves attack old moose and young calves.

“Many moose died in 1996,” he said, “so the average moose is only five or six years old. There a lot of young adults, which are hard moose to bring down.”

The Isle Royale wolves continue to reside in three packs. “The territorial skirmishes seem to have settled,” Peterson said. “There was one lone wolf killed by a pack.”

Peterson also said that all three packs should have litters of pups in late April.

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


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