NATIONAL PARK SERVICE Wolf Ecology and Prey Relationships on Isle Royale

Distribution of 107 calf moose killed by wolves in midwinter, 1959-74.

1975 and 1976. The Isle Royale wolf population continued to increase in 1975 and 1976, following the trend detailed above. In February 1975 the island supported 41 wolves, and we witnessed the establishment of a third pack, the Middle Pack, between the East and West packs. The Middle Pack appeared to consist of an adult pair and five pups. The East Pack reached a peak of 18 wolves, while the West Pack dropped slightly to 10 members. A trio and a loner also were found at the southwest end of the island, and there was a duo in the middle.

In 1976 the winter wolf population totaled 44, broken down as follows: 17 in the East Pack, 9 in the West Pack, 4 in the Middle Pack and an adjacent group of 3 that probably had split off this pack, plus additional groups of 4, 3, and 2, and 2 loners. In February the West Pack attacked the pack of 4 wolves within their territory and killed two of them.

Established trends in the moose population continued: calf production and survival were low, and predation increased as the wolf population continued to grow. In contrast to the early 1970s, wolves again began to prey intensively only on calves and old adult moose. Details of the wolf population and wolf-moose relationships in the post-1974 period will be published at a later date.