The rise and fall of Isle Royale wolves, 1975-1986

Document Type

Article

Publication Date

1-1-1988

Abstract

The Canis lupus population in Isle Royale National Park, Michigan, increased steadily in the 1970s, reaching a peak of 50 wolves (91 wolves/1000 km2) in 1980. A population crash followed in 1980-1982, then wolf numbers stabilized at 20-24, the same level as during the 1960s. After a lag of 2-3 yr, wolf density followed trends in moose Alces alces mortality rate, which was correlated with wolf-pack food supply. The increase in numbers of wolves resulted from proliferation of reproducing packs when food became more abundant in the early to mid-1970s. During the increase phase, pack size averaged 9.5 wolves, with annual survival of 84-87%, but during the crash, pack size dropped to 4.7 and survival was 49%. Equilibrium was reached in 1983-1986, with average pack size of 6.5 and annual survival of 66-67%, coupled with annual recruitment of 2 pups/pack. For 2 yr before the 1980-1982 crash, dispersal of individuals from packs was high, resulting in smaller pack size. Known mortality during the decline took the form of starvation and intraspecific killing, direct and indirect manifestations of reduced food supply. -Authors

Publication Title

Journal of Mammalogy

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