A plague of ticks, stifling hot summers and relentless pressure from wolves have driven the moose population on Isle Royale National Park to its lowest ebb in at least 50 years.
Their numbers have sunk from last year’s record low of 450 down to 385, the lowest since researchers began tracking their numbers on this wilderness Lake Superior archipelago. Now in its 49th year, the project is the world's longest-running study of predator-prey relationships.
“Along with this is an even more impressive decline in wolves, from 30 to 21,” said John Vucetich, an assistant professor at Michigan Technological University. “The main reason is a lack of food.” For wolves, that translates into a lack of moose.
In 2002, the island was home to more than a thousand moose. Since then, unusually warm summers have dealt a double whammy to the big herbivores: They lose their appetites and seek shelter from the heat, putting them in a worse position to survive winter. And the climate change also seems to favor ticks, causing a massive infestation that has yet to abate. Fortunately for human visitors to the island, the ticks have no interest in people.
A single moose, however, can host tens of thousands at a time, and each tick can suck up about a cubic centimeter of blood. Rather than browse, the moose scratch themselves against trees or bite their hair out trying to remove the parasites. Weight and blood loss often prove deadly.
Wolves are responding to the dwindling of their food supply as they have in the past: with internecine warfare.
Last year, Vucetich witnessed members of the island’s East Pack attack and kill the alpha male of the neighboring Chippewa Pack. This year, they got his widow, the alpha female.
“All we found were the skull and a radio collar,” said Rolf Peterson, a research professor of wildlife ecology at Michigan Tech. “It was nice they left the skull; foxes tow them around, and we might never have found anything.”
The pair that were killed were founders of the Chippewa Pack. Their lupine love affair began in 2000, when Peterson witnessed the female fleeing into the icy waters of Lake Superior to elude members of another pack intent on her demise. The attackers finally left her for dead on the shoreline; then a lone male roused her, licked her wounds and helped get her on her feet. In the years hence, the happy couple had raised seven litters of pups.
“That’s way above average in terms of progeny,” Peterson said. “She’s the number two all-time breeder in the study.”
“Amazingly, the Chippewa Pack has hung on; they are now under new leadership,” Vucetich said.
Hard times are cascading down to other carnivores. With a shortage of moose meat, wolves are consuming virtually every morsel. “Out of a 900-pound animal, all that remained was a couple of bones. Even the skull was eaten,” Vucetich said. “That’s a sign of tough times for wolves.”
Thus, almost nothing is left for smaller predators and scavengers. “Foxes are having a very hard time,” Peterson said. “Hares are at a cyclical low, and there’s very little left for the foxes to scavenge.”
Yet, in the midst of great privation, there are indications that a new pack may be forming.
“A couple is showing territorial signs, scent marking, and has killed about three moose,” Vucetich said. “It doesn’t really count until they breed, but it’s kind of interesting that in the middle of all these hardships, they are setting out on their own.”
“Someone,” says Peterson, “is always trying to enlarge their footprint.”
The Isle Royale wolf-moose study is funded by the National Park Service, the National Science Foundation and Earthwatch.
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