Ecological Studies of Wolves on Isle Royale

Peterson, Rolf

On Isle Royale, the wolf population continued to increase during the past year, from 25 to 29 wolves, and in 2000 it was higher than in any point since 1980. Mortality during the past year (4%) was exceptionally low, and a total of five pups were raised in two packs. The wolf population is apparently being restructured, from three territorial packs to just two; the Middle Pack began to take over West Pack terrain in 1999, and the takeover appeared complete in 2000, with Middle Pack claiming 75 percent of the island area (and about half the moose). The Middle Pack (with up to 12 wolves) and the East Pack (now 10 wolves) together claim the entirety of the island. Moose on Isle Royale were little affected by winter conditions in 1999-2000, but winter ticks prompted by warm spring and summer weather in 1998 appeared responsible for malnutrition deaths recorded in late winter and spring 1999. Calf abundance in winter 2000 was exceptionally low (6%), and the population was estimated at 850 moose, up slightly from the 1999 estimate. Plant species favored by moose have enjoyed more favorable growth conditions since 1996, when over three-quarters of the moose population died of starvation, yet some woody plants may not recover normal vigor because of previous overbrowsing.