Ecological Studies of Wolves on Isle Royale - Annual Report 1996-1997

Peterson, Rolf

The aftershocks of the moose crash during the winter of 1995-1996 continued well into May, 1996, when delayed arrival of spring caused an extended period of starvation for moose. Only 500 moose survived at census time in February 1997, down from 2400 in 1995. Wolves managed a modest increase in the past year, from 22 to 24 animals, including seven surviving pups distributed among two territorial packs and a new breeding pair. Moderate reproduction in the wolf population was almost offset by increased mortality. Even with very abundant food during the first half of 1996, no wolf pack brought through more than 3 pups to winter 1997, and one territorial pack contained no pups. During 1997 kill rates of moose were near normal for territorial packs, but it was clear the wolves were having difficulty finding prey. There were no known turnovers among breeding individuals in territorial packs. A record 175 dead moose were examined in 1996, with starvation the most common cause of death. Although calves and old moose predominated among the dead moose, many young adults also succumbed. The 1996 cohort of moose calves was small in stature and abundance, comprising only 3% of the moose population in winter 1997. Wolf:moose ratio has increased seven-fold in the past two years, and wolf predation may now limit moose population increase. A recovery of moose forage plants is expected.