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Fauna Series No. 7







Study Area

Isle Royale Mammal History

Methods and Extent of Present Research


Wolf-Moose Coaction




Fauna of the National Parks — No. 7
The Wolves of Isle Royale
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Wolf Numbers

wolf tracks
Figure 33—Wolf tracks in snow.

The composition of the Isle Royale wolf population makes possible a reasonably precise count but renders difficult an absolutely complete census. The main pack, containing 15 to 16 members, usually was relatively easy to locate. However, groups of three and two, and lone individuals, also were sighted. (These smaller groups were difficult to find and keep track of.) Thus, censusing involved finding and counting the large pack and then trying to locate all other groups. The wolves' preference for traveling along the Isle Royale shore or on lakes was most important in the success of the censuses.

Censuses were attempted on the first or second day after a fresh snowfall, or under the following combination of circumstances: (1) the known whereabouts of the large pack, and (2) the discovery of a recent kill made by another pack (thus often allowing the prompt locating of this pack), and/or (3) the accidental sighting of other wolves. During censuses, we flew at 300 to 500 feet altitude and surveyed the entire shoreline and all major lakes for wolves or tracks (figure 33). Tracks were followed until the wolves were found, if possible. Undoubtedly, no large packs escaped detection, but perhaps one or two lone wolves did.

On February 9, 1959, after a fresh snowfall, the first census was made. A pack of 15 wolves was discovered near McCargo Cove, a lone wolf at Todd Harbor, and another individual in Rock Harbor. A search of the rest of the island produced no other wolf sign. However, on February 23 a pack of 3 was sighted near Five-Finger Point, and a few minutes later the pack of 15 plus a lone wolf were discovered near Davidson Island, demonstrating that at least 19 wolves were present. The extra lone wolf seen February 9 might have been a straying member of the pack of three. No other wolf sign was seen in 1959 which could definitely be attributed to any other animals.

In 1960, four groupings of wolves were noticed: 15 (plus a lone wolf which followed this pack closely), 3, 2, and 1. The two wolves were seen three times, and the pack of three, five times, all on the same half of the island, but both packs never were observed on the same day. Therefore, I thought that perhaps the two wolves were part of the pack of three, and that the single wolf (only noticed once that year) was the third animal. The total estimate remained at 19 or 20.

wolf tracks
Figure 34—Tracks of five wolves in sand.
wolf tracks
Figure 35—Wolf tracks in snow.

Therefore, the 1961 estimate of the number of wolves present on Isle Royale is 21 and possibly 22. The difference between estimates in 1960 and 1961 is caused only by the difference in interpretation of the observations. That the pack of two was not seen in 1959 does not mean it was not present, for during that year even the pack of three was observed only once, whereas in subsequent years it was seen many times. I believe that the Isle Royale wolf population has remained unchanged for the duration of this study. My increasing familiarity with the island's wolves from one study period to the next merely has made the last census most precise.

The census in 1961 was complicated by the fact that the large pack often split up. Nevertheless, this pack still contained 15 animals. Lone wolves and the pack of three again were sighted several times. This year, however, strong circumstantial evidence indicated that an additional pack was present, composed of two animals. Although this never was proved conclusively, general knowledge of the Isle Royale wolves makes me believe that the group of two animals seen in 1960 and 1961 was not part of the pack of three.

wolf tracks
Figure 36—Wolf tracks in sand.

wolf tracks
Figure 37—Wolf tracks near kill.

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