Thursday, March 09, 2006

Isle Royale moose numbers continue crash


The number of moose on Isle Royale dropped to 450 this winter, the lowest level since scientists began tracking the animals nearly a half-century ago. The moose population is down from 540 last year and is just a fraction of the all-time high moose population of 2,442 in 1995.

The number of wolves on the island are holding steady at 30, according to the annual survey by Michigan Technological University researchers. But that may not last as moose become too scarce to feed the island's three wolf packs.

The winter survey, the 48th annual, is the longest-running predator-prey study in the world.

Moose have been declining for years because of unusually warm summers on the Lake Superior island and extremely high winter tick infestations. Moose eat less when it's warm and are less able to survive winter. And tick infestations appear to be worse during winters with shorter snow seasons.

Moose also have been eating themselves out of the best food on the island, which sits about 20 miles off Minnesota's North Shore. Scientists say some moose are becoming dehydrated in winter because they aren't getting enough moisture from their food. Moose were observed eating snow in recent years, a rare phenomenon.

"That's extremely unusual. It's something that, throughout the world, when you talk to moose biologists, you just don't see," said John Vucetich, assistant Michigan Tech professor who conducts the study with biologist Rolf Peterson.

The island's forest has been changing from mostly birch and aspen, which is prime moose food, to less nutritious spruce and balsam fir. That's also caused a decline in beaver, which wolves feed on, too.

Moose are so hungry that they're eating lichens. "A 1,000 pound animal eating lichens! It's like eating dust," Peterson said.

But it's the relatively high number of wolves on the island that are doing the most to keep moose numbers down.

"The moose are getting eaten by the high number of wolves. With moose numbers so low, we would have expected to see wolf numbers drop by now. But they haven't," Vucetich said. "That really surprised us."

There are now about 15 moose on the island for each wolf. That ratio should be about 40 or 50 moose for each wolf. On average, wolves each consume about seven moose a year.

Researchers were literally watching moose drop during their winter survey on the island, a national park and the largest island on Lake Superior. Wolves have had to turn from eating sick and old moose, which are now gone, to eating calves and trying to take down healthy moose.

"We had two dozen moose die while we were there this winter," Peterson said. "Moose are really going to go down, unless the wolves back off."

Wolves on the island are showing signs of having to work too hard for their food, including "chaos" within and between packs. Survey crews even witnessed one pack ambush, attack and then kill the alpha male of another pack.

This inter-pack warfare is not by chance, scientists say. It's a struggle for control of a declining food supply.

Eventually, scientists say, wolf numbers will crash, giving moose a chance to rebound. By then, habitat could also improve with fewer moose gnawing on trees. The change to dropping wolf numbers and increasing moose should happen this year and show up in next winter's survey, Vucetich said.

Still, scientists say that both species have surprised them before. The last time it seemed there were too many wolves for the number of moose on the island, canine parvovirus hit and nearly wiped out the wolves.

It's believed that moose first swam to the island in the early 1900s and for decades thrived with no predators.

Wolves are relatively new to the 45-mile-long, 143,000-acre island complex, having crossed Lake Superior ice to get there in 1949. Their numbers have ranged from 11 in 1993 to 50 in 1980.

Peterson and Vucetich track moose and wolves to see what effect changes in one species have on the other, all in an environment having little human interference and no competing species such as deer or bear. The animals can't leave the island, and there are no vehicles, poachers or hunting to affect the population.

If there was an equilibrium between the species on the island, it would be about 25 wolves and 1,000 moose, Peterson has said. But that level is almost never reached -- one of the two species is almost always out of balance.

The annual study is funded by the National Park Service, the National Science Foundation and Earthwatch.

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