Fauna Series No. 7

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

RESULTS—THE TIMBER WOLF AND ITS ECOLOGY

Home Ranges and Territoriality

Evidence that wolves are territorial was presented by Murie (1944) and Cowan (1947), and Stenlund (1955:37) wrote:

Travel routes [in Minnesota] suggested established home ranges with poorly defined borders overlapped somewhat by ranges of other packs. Home ranges from which the main pack had been removed remained barren of sign for two or three weeks after which other wolves reoccupied the range. Since these vacated home ranges remained free of wolves for a period of time, it is probable that wolves and wolf packs on the periphery respected the established territory of the home pack.

Schenkel (1948) believes that urine sprayed on scent posts serves to mark territories. This may explain Young and Goldman's (1944) report that urine from a strange wolf causes great excitement in other wolves and that scratching and kicking up of dirt, and often excessive deposits of excreta, are noted when such urine is found on scent posts.

Isle Royale's packs also seem to be territorial, at least in winter. Although the large pack used all parts of the park, it frequented certain sections much less than others. During 5 weeks in 1959, this pack only once visited the northwest shore from Duncan Bay to Thompsonite Beach, and spent but 4 days there. For the remainder of the period, the animals used the southeast side of the island (figure 41). In 7 weeks of 1960 the pack spent a few days on part of the northwest side, but continued to use the southeast half extensively (figure 42). However, in 1961 the range of the large pack seemed to have shifted somewhat. The southwest end of the northwest shore was used more, and the northeast end of the southeast shore, less. Even so, most activity of this pack occurred on the southwest end of the southeast side, as it had in 1959 and 1960 (figure 43). The shifts in range during the three study periods may have been apparent only, because throughout most of the year the wolves may have used many other regions than indicated in the figures.

Figure 41—Territory of the large pack—February through March 1959.
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Figure 42—Territory of the large pack—February through March 1960.
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Figure 43—Territory of the large pack—February through March 1961.
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The only summer observation of wolves which probably were members of this pack was reported by K. Knoble of Gays Mills, Wis. On July 17, 1958, he saw six wolves on the Huginnin Cove Trail. Tracks of a pack of five were seen in August 1960 and May 1961 along the southeast and southwest shore of Isle Royale, and a large group was heard howling north of Siskiwit Lake in June 1960. All these locations are within the winter range of the pack of 5. A large pack also was heard several times near Daisy Farm in Rock Harbor, a less-used section of the winter range.

Thus the winter range of the large pack could be considered to be about half of Isle Royale, or 105 square miles. The approximate density of wolves in this territory, then, would be one animal per 6.5 square miles. It probably is significant that this area contains the best moose range and about two-thirds of the winter moose population. Of course, it might be more appropriate to consider the whole island as the range of this pack, since the entire area is available to the wolves, and indeed they do occasionally visit all of it.

The pack of three and the pack of two frequent the northwest side of Isle Royale, apparently with complete coincidence of territories (figure 44). Four summer observations of three wolves were all made in regions within the winter territory of the pack of three. Campers saw three wolves at the head of Tobin Harbor about August 20, 1958, and Milford Johnsson observed three in October 1958, near Amygdaloid Channel. On July 28, 1960, Park Service Naturalists Robert A. Janke and Robert G. Johnson spotted three wolves just northwest of Mount Ojibway, and on August 20, 1960, Prof. and Mrs. W. Warth of Oberlin, Ohio, frightened three animals from a kill along the Huginnin Cove Trail.

Figure 44—Territory and observations of the small packs—February through March 1959-61.
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Since the two smaller packs range over about half of Isle Royale, the approximate density of wolves in their territory is one animal per 21 square miles, about one-third the density on the other half of the island.

The average approximate density for the entire island is one wolf per 10 square miles, but this figure should be viewed cautiously because of the disparity in densities between the two sections of the island. Wide differences exist among figures reported from other areas, but Isle Royale has one of the highest densities recorded. Stenlund (1955) estimated that northern Minnesota supports one wolf per 17 square miles. For three study periods in Saskatchewan, Banfield (1951) estimated densities of 39.5 square miles, 58 square miles, and 83 square miles per wolf. Cowan (1947) believes that in Jasper National Park there was one wolf per 87 to 111 square miles in summer, but one per 10 square miles in winter. Reported home-range sizes of individual packs are listed in table 7.

TABLE 7.—REPORTED HOME-RANGE SIZES OF INDIVIDUAL WOLF PACKS

a If the entire island were considered to be the range, this figure would be 210.

b If the entire island were considered to be the range, this figure would be 13.

The winter range of the smaller Isle Royale packs overlaps with that of the large pack in the Rock Harbor and Washington Harbor areas. It is interesting to speculate whether the smaller packs chose to inhabit the portion of the island with proportionately fewer moose or whether they were forced there by the large pack. Murie (1944:44) wrote that ". . . it is advantageous for minor packs to find territories where they are unmolested." This may be especially important on Isle Royale because of the great numerical difference between the large pack and the smaller ones. Schenkel (1948:90), during a study of wolf behavior, concluded that ". . . as soon as the society controls a certain number of individuals, the manifestation of all individuals toward individuals from outside becomes more secure. . . ." Thus, it appears that the smaller packs probably have been forced to inhabit the part of the island in which they are least molested.

Two instances were observed of direct encounters by the large pack with other wolves. On February 7, 1960, the 16 wolves chased a single animal at least halfway across Moskey Basin (about one-half a mile) to the north shore of the bay. All ran extremely fast, but the pursued wolf outran the others. Upon reaching shore, it continued at top speed into the woods and then northeastward at least a quarter of a mile without stopping. The pack gave up when it reached shore, and the animals lay down and rested.

The second instance was observed on March 4, 1961, near Cumberland Point. The large pack was traveling along the shore from Rainbow Cove to Cumberland Point when two wolves, which had been feeding on an old kill, ran out of the woods about 125 yards ahead. The pack gave chase, and the larger of the two wolves headed into the woods and was not pursued. The smaller individual continued with utmost haste for a few hundred yards along the shore, stopped momentarily, looked back at the oncoming animals, and assumed the attitude of complete submission described by Schenkel (1948), i.e., front legs stretched forward and head and shoulders lowered. After a few seconds, it turned and headed along the shore, with the pack in continued pursuit. All ran swiftly, but the pack did not gain on the lone wolf. The pursuers stopped after covering about one-half a mile; the single wolf continued at the same speed for at least another mile before entering the woods.

There also were indirect indications of enmity by the large pack toward outside wolves. On March 6, 1960, the pack of three ran "anxiously" from Grace Island to Washington Island while the 16 wolves were heading across Grace Harbor, a quarter of a mile away. Grace Island prevented each pack from seeing the other, but the 16 animals kept looking toward the 3, which were running and watching their back-trail. The large pack did not pursue. On February 22, 1960, the large pack was traveling overland south of Ishpeming Point when suddenly half of the wolves struck out on a fresh wolf track. They followed it excitedly for about a quarter of a mile before returning to the others.

Figure 45—Part of large pack traveling along shore of Washington Harbor.

The actions of the pack of 15 to 16 toward other wolves gives the impression that if the dominant animals ever caught the outsiders, a mortal fight would ensue. Indeed, Cowan (194?) reported an instance related to him in which a large wolf was found mangled by others, and another instance in which four wolves attacked a fifth and wounded it badly. He also wrote of a situation in which a wolf wounded a dog and then rushed it again as its master leaned over it. Cowan believes the wolf's action was a manifestation of territoriality. Murie (1944:43) also described an observation of a wolf pack wounding an alien wolf. On Isle Royale, Cole (1956) found tracks indicating that a pack had attacked a strange wolf. Bloody snow and a 2-inch piece of lip showed that a serious fight had ensued.

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