From the Duluth News Tribune, by John Meyers
Battling unusually warm weather and an unrelenting infestation of ticks, moose of Isle Royale are continuing to die off at a rapid rate.
Only 540 moose were on the island this winter, down from 740 last year and less than half of the 1,100 found two winters ago, Michigan Technological University researchers found.
"Moose numbers have been cut in half in the last three years. That's pretty remarkable," said Rolf Peterson, the Michigan Tech researcher who has been charting the island's moose/wolf relationship for 35 of the study's 47 years.
The island's wolves, however, seem to be doing just fine, holding steady at 30 this year compared with 29 last winter and up from 19 in 2003. Ten wolves died in the past year, but 11 new pups survived to this winter.
It's the tick trend, spurred by warmer weather, that most concerns scientists. Last year for the first time, Peterson said, global climate change may be affecting Isle Royale enough to be spurring the problem.
When moose get too warm, they don't eat, and if they don't eat, they are less able to survive the cold spells of winter or outrun wolves. Warmer weather also may mean more moose ticks.
"Last summer, the average moose had lost more than 70 percent of its body hair due to ticks," said John Vucetich, research assistant and a 10-year veteran of the island study. "This is about twice the hair loss of just a few years ago. A moose with 70 percent hair loss could have been carrying in excess of 70,000 ticks during the winter and early spring."
This particular tick species doesn't pester humans. And while ticks are a periodic problem for moose across their range, it's not clear why tick numbers are exploding now on the island. Some biologists have speculated warmer springs may be a factor. If ticks fall off moose in April and hit snow, they die, Vucetich said. If they hit bare ground, they lay more eggs.
"But nobody really knows," he said.
While the island's three wolf packs are thriving off dead and dying moose, researchers say wolves may be "riding the caboose of the moose gravy train."
"There were only 18 moose per wolf this year, the lowest ratio we've ever had," Vucetich said. That ratio is usually between 30 and 70 moose per wolf. On average, wolves may each consume about seven moose a year.
Moose on the island have crashed before and bounced back, going from 2,500 to 500 in the mid-1990s and then returning to more than 1,000. Currently, researchers note that moose seem to be eating themselves out of their favorite foods, including balsam fir, and that the island may be suffering long-term forest changes because of moose munching trees.
Still, scientists say that both species have surprised them before. The last time it appeared that there were too many wolves for the number of moose, Peterson said, canine parvovirus hit and nearly wiped out the wolves.
"Can the wolves do it again, or will wolves take a huge hit next year because they're overextended?" Vucetich said.
Jean Battle, Isle Royale National Park biologist, said it's unlikely the Park Service will take action to stop the forest decline where it's occurring, noting most of the island is a federal wilderness where nature is allowed to run its course.
"There are all sorts of studies going on looking at vegetation and moose... But it's not something we're going to manage," Battle said.
On Isle Royale, about 20 miles off Minnesota's North Shore, moose numbers hit a high of 2,422 in 1995 and bottomed out at 500 in 1996.
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.
The study is the longest-running predator/prey research in the world. Peterson tracks 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.
