Earthwatch-supported research suggests that shifts in the balance between moose and wolves on Isle Royale, Michigan, may result from changing climate.
Many scientists predict that global climate change will affect wildlife and plant population levels and challenge their very survival in the foreseeable future. Recent findings regarding the wolves at Isle Royale National Park and their primary prey, moose, suggest the imminence and complexity of these population changes.
The moose population at Isle Royale, a wilderness island park in Lake Superior, has slid to 750, down from 900 last year and 1,100 in 2002. In the meantime, the number of wolves has seesawed upward over the past decade and is now up to 29, as many as the park has seen since 1980 and 11 more than last year. Researchers suspect that a global warming trend may be behind the shift.
"What we think is happening is that wolves are cashing in on moose vulnerability that's been induced by a warmer climate," said Dr. Rolf Peterson (Michigan Technological University). Peterson has led the study of Isle Royale's wolves and moose for 34 years, and is principal investigator of the Earthwatch-supported Moose and Wolves project.
Earthwatch teams have been assisting Peterson's research on Isle Royale for 17 years, monitoring trends in moose kills and winter-starved animals by bushwhacking through the forest in search of their remains. Their findings show that moose and wolf populations peak and fall at staggered intervals, one typically triggering the next, but recent data also indicate a climatic influence.
What's bad for moose has been good for the wolves, according to Peterson. Moose throughout North America have been hit hard by warmer temperatures that began in 1998 with El Niño and never let up. On Isle Royale, the moose population was stressed by a drought in 1998 and then a particularly warm autumn in 2001.
"Moose can't feed in the summertime if it's too hot," Peterson said. "They have a big fur coat on, and they can't sweat. They just sit in the shade or in the water." Moose that don't eat enough become weak, sickly, and easy prey for wolves during the winter. "Warm weather in spring and fall also leads to ticks the following winter, and ticks can kill moose."
A single moose can be host to tens of thousands at a time, several per square inch, 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 such a handicap that the moose often don't survive.
As the moose population has struggled against the heat and ticks, the wolves have thrived, largely because it's been easier for them to bring down their biggest prey. The wolves are killing about twice as many moose as they did last year, so the warmer temperatures apparently allow them to maintain their peak population.
"In this region, climate change has involved warmer winters, especially in the late 1990s and early years of this century," Peterson said. "We couldn't anticipate the effect for moose, because warmer winters mean less snow and more tree growth, which helps them. But it also leads to more ticks, and it impacts their feeding. With two pluses and two minuses, there was no way to forecast how it would come out in the wash. But it looks like it might be to the detriment of moose."
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