Fauna Series No. 7

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

RESULTS—THE TIMBER WOLF AND ITS ECOLOGY

Packs

A summary of the size of Isle Royale wolf packs observed before and during this study is presented in table 6. Because larger packs sometimes break up into smaller groups, single observations are not always reliable for determining the size of a pack. Nevertheless, it is interesting that sightings recorded before 1959 involved some groupings of the same size as those seen during this study.

TABLE 6.—SIZES OF WOLF PACKS OBSERVED ON ISLE ROYALE

Hakala (1954) observed two wolves along the Feldtmann Trail in 1952, and Cole (1956) found evidence of a pair in 1956 near Siskiwit Bay. In 1960 and 1961, a pair (one animal larger than the other) was observed only on the northwest side of the island. Perhaps a pack's territory changes as variations occur in the size or distribution of other packs in a discrete population. If that is so, this pair may be the same as that observed in previous years.

Each winter a pack of three frequented the northeast and northwest parts of the island, where Cole (1957) four times observed a group of three. Probably these are the animals observed by Cole. One of the members is smaller than the others, so it may be a female.

The most significant pack on Isle Royale usually contains 15 to 16 members. This pack probably represents some combination of the seven wolves and the four observed by Cole, and the offspring of either or both groups. It has the largest (and probably best) range, kills the most moose, and dominates in encounters with other wolves. Most of each winter study period was devoted to observing this pack.

Figure 38—A typical formation of the large pack.

During the winters of 1959 and 1960, members of the large pack usually remained closely associated (figure 38). The few times the pack did split up in 1959, it usually separated into groups of 10 and 5 to 6. The smaller group sometimes continued to rest for about an hour after the other animals started traveling, and it occasionally lagged on long treks. Twice, 5 wolves headed for old kills while the other 10 continued hunting. (In August 1960 and May 1961, tracks of a pack of five were observed along the winter runway usually used by the large pack.) Within the group of five, three animals seemed lighter colored and lankier, and these were thought to be young-of-the-year. If they were, this might explain why the group rested longer and more frequently.

Figure 39—Moose trail used often by wolves in summer.

In 1960 the large pack still contained 15 to 16 members, but the 3 lanky wolves were not evident among them. The only time we observed any break-up of the pack was during the last 4 days of the study period, March 17 to 20, when three animals were missing.

However, in 1961 this pack was split about half of the time. On 13 of the 25 days the pack was observed, it was divided, usually into 5 and 10, or 7 and 8. There also were indications that it might have been losing a member, for often when the groups were united, only 14 wolves were present. In Alaska, Burkholder (1959) studied a pack which usually numbered 9 or 10 but sometimes split into 3 and 7.

Within the large pack there appeared to be at least three females, as determined by their behavior during the mating season. One of these, the smallest individual in the pack, was accompanied closely by a large male for a few weeks each winter. This pair, part of the 10 when the pack split in 1959 and in 1961, was the only pair that was consistently evident in the pack.

At least one lone wolf has been seen each year of the present study and of Cole's studies. In 1957 one followed Cole and his pilot for 9 miles across Siskiwit Bay. Cole (1957) believed this may have been Big Jim, the tame wolf released in 1952.

Figure 40—View toward Canada (Sibley Peninsula, Ontario, 20 miles in background) from interior of Isle Royale.

The lone wolf studied during the present investigation followed the pack of 15 from February 23 at least to March 14, 1959. Usually, it remained about 100 yards behind the pack and often was chased. Throughout the 1960 winter study period, a lone wolf (assumed to be the same one) again followed the pack, but it seemed almost to be accepted. It still traveled behind the others and did not mingle much, but only on February 22, when much mating activity occurred, did I see it run from them. On that occasion, whenever they looked or moved toward the animal, it ran and then followed the group from a distance. The relationship between the pack and this individual in 1960 is difficult to describe, but it seemed more a matter of strong tolerance by the pack than complete acceptance. Therefore, the basic size of this pack is considered 15 animals, although sometimes the "pack of 15 to 16" or the "15 to 16 wolves" will be referred to.

In 1961, two lone animals frequented the large pack's territory, and they could not be distinguished. Neither followed the pack consistently. One was probably the same individual seen in previous years, and the other presumably was the straying 15th member of the pack. Neither was exceptionally small, so both probably were males.

Other single wolves were seen each winter, but these may have been just straying members of the packs.

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Last Modified: Thurs, Jul 4 2002 10:00:00 pm PDT
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