There were about one-third fewer wolves on Isle Royale in early 2001 than there were last year, but those that remain are experiencing the best of times, according to Dr. Rolf Peterson, a Michigan Tech wildlife biologist. Peterson has directed annual surveys of the predators for the National Park Service for the past 31 years. He says the 2001 survey showed total wolf numbers had dropped to 19 from 29 a year ago, mostly because of inter pack warfare and a decreased crop of moose calves born in 1999, following the hot, dry summer of 1998.
“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. The hot, dry summer of 1998 made life difficult for moose because they don't perspire like people do - instead they become overheated and hyperventilate and have to use a lot of energy just trying to keep cool. Those same 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 - and calves provide the most reliable prey for wolves.
With heavy snow cover on Isle Royale in early 2001, wolves in the National Park are having a much easier time. "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. This is about as good as it gets for a wolf."
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."
Peterson said the park's moose herd has increased slowly since the summer of 1996 and now numbers about 900 animals. He said a major challenge for moose on Isle Royale lies in the poor winter food supply, especially on the west end of the island, where the animals often have to try to survive on lichens. Moose on the east end fare better because of the large balsam fir stands growing there.