Ecological Studies of Wolves on Isle Royale - Annual Report 1995-96

Peterson, Rolf

Dramatic changes occurred at Isle Royale in the past year, with wolves increasing to their highest level in over a decade (22 individuals) while the moose population crashed from lack of food (to about 1200 individuals), a condition exacerbated by winter ticks and severe winter weather. The wolf population included seven pups distributed in all three territorial packs. Wolves increased as mortality remained low and reproduction was high. Notably, the first litter of pups born to wolves of the next generation was of normal size, with four pups surviving to winter. Three pups survived in the other two territorial packs. Wolf age structure is now dominated by young wolves with high expected survival rates and reproductive potential. Reproductive potential of the next generation of wolves will provide a test of the consequences of inbreeding in this population, known to have lost genetic variability because of geographic isolation. In the moose population, low calf survival and retarded body growth in calves were evident in summer 1995, and high loads of winter ticks were already causing hair loss in January, 1996. Deep snow then aggravated a severe shortage of winter forage, and the combined impact of these conditions led to the highest moose mortality rate of the past 38 winters. Significant causes of death in winter were wolf predation, starvation, and falling over cliffs while foraging. Because of poor calf production and survival, plus an increasingly old age structure, the moose population should continue to decline from the historic high level recorded in 1995.