Wolves Feast Well on Isle Royale
There are fewer wolves on Isle Royale this year than last, but those that remain are experiencing the best of times. The latest results from a classic long-term study of wolves on Isle Royale National Park, Michigan, continue to provides instructive examples of how wolves interact with the northern forest ecosystem.
Dr. Rolf Peterson, a wildlife biologist from Michigan Technological University and leader of the Earthwatch-sponsored Moose and Wolves project, has directed annual surveys of the predators for the National Park Service for the past 31 years. Peterson said the just-completed 2001 winter survey showed total wolf numbers had dropped to 19 from 29 a year ago, but that these animals are thriving on an abundant crop of moose calves.
"This is about as good as it gets for a wolf," said Peterson. With heavy snow cover on Isle Royale this winter, wolves in the national park are having an easy time catching prey. "The 2000 calf crop produced between 200-300 animals," said Peterson. "And heavy snow makes traveling tough for calves, so this winter wolves have the advantage and two-thirds of all the moose kills we examined were calves."
The reduction in wolf numbers is a consequence of both inter pack competition and a decreased crop of moose calves born in 1999. Peterson said the island's West Pack has been eliminated and their territory taken over by the Middle Pack, which numbers six animals. The East Pack, also numbering six wolves, has maintained its territory on the moose-rich east end of the island.
"There is a third pack of just a reproducing pair and one surviving pup that has carved out a territory for itself on the northeast side of the park and the other packs have respected its territory," said Peterson. "There is also another mated pair and two single wolves wandering about the island and making do as best they can." These ongoing territorial adjustments and conflicts are in turn linked to changes in the wolves' prey resources.
The poor crop of moose calves in 1999 was a result of the hot, dry summer of 1998. Adapted to temperate summers, in hot conditions moose can become overheated and hyperventilate and have to use a lot of energy just trying to keep cool. These conditions led to an increased tick infestation the following winter, which further weakened the island's moose. The result was that probably fewer than 100 calves were born in 1999, a relative dearth of the most reliable prey for wolves.
In addition, minimal snowfall last winter put wolves at a disadvantage against their prey. "Mild winters like we had in 2000 may be welcomed by humans, but they can be tough on wolves that rely on moose for their main source of food," said Peterson. "When snow cover is light, moose can move around easily and are much more difficult for wolves to catch and kill." During the easy winter of 2000, wolves on Isle Royale weren't able to kill as many moose as they needed to maintain robust health.
This winter has represented a significant improvement in prey availablity for the wolves on Isle Royale, and Peterson reports that all the wolves seen in the park this winter seemed in good health. With wolves reappearing in several parts of their former range in the U.S., through reintroduction programs and immigration, Peterson's study stands to provide critical data on the predators' role in forest ecology.
Each spring and summer Earthwatch volunteers bushwhack through the Isle Royale's rugged backcountry to add to Peterson's findings. By monitoring trends in moose kills and winter-starved animals, participants in this landmark study continue to demonstrate the interdependent relationship between wolves and moose, with implications for wolves and other predators around the world.
For information on volunteering on Peterson's project, see Moose and Wolves
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