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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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The topography of Isle Royale is characterized by series of parallel ridges and valleys, narrow points and bays, numerous nearby islands, and slender lowlands and lakes. The island originated when a bed of pre-Cambrian lava and sedimentary layers faulted, tilted upward from southeast to northwest, and protruded from the sea. Erosion, submersion, and deposition of Cambrian sediment followed, and the process was repeated. "Similar processes continued until the marked elevation of the land, which took place at the close of the Tertiary, and which initiated the repeated glaciations of the Ice Age" (Adams, 1909:32).

The last (Wisconsin) ice sheet completely covered Isle Royale by several thousand feet. After it receded, Lakes Duluth and then Algonquin covered the island. Eventually, new outlets developed and the lake level dropped by steps, as evidenced by the ancient beach lines seen today on Isle Royale and the north shore of Lake Superior (Adams, 1909). The present lake level is 602 feet.

Because of the direction of the original tilting, the southeast sides of most ridges slope, whereas the north west sides form escarpments. One main central divide, the Greenstone Ridge, extends the length of the island. Its summit, Mount Desor (elevation 1,394 feet), is the highest point on Isle Royale. Minong Ridge and Red Oak Ridge parallel this on the northwest and southeast, respectively. These and numerous lesser crests produce a "washboard effect." At the northeast end of the island, ridges project for miles into the lake, forming points, peninsulas, and over 200 surrounding islands (figure 4).

aerial view
Figure 4—Aerial view of northeast end of Isle Royale.

aerial view
Figure 5 —Northward view of the south-central section of Isle Royale, well used by wolves every winter.

The soil is shallow, sandy or stony loam; there is little glacial till. Postglacial disintegration of rock, plus deposition of organic remains, has produced most of the soil, but lacustrine clay and sand are present in isolated locations (Adams, 1909). Erosion has left many ridgetops bare or covered with thin, azonal soil, whereas deposition has built up many poorly drained valleys. Where accumulation has occurred in upland areas, there has been light podzolization (Linn, 1957).

Between the ridges there are hundreds of ponds, swamps, and bogs, and approximately 30 lakes. Siskiwit Lake, the largest, is 7 miles long and 1-1/2 miles wide. Most watersheds are small, so many streams are intermittent; the few permanent ones are slow-moving. Numerous narrow bays, harbors, and channels interrupt the shoreline, particularly along the northeast half of the island. In winter, these frozen waterways provide landing fields for the research aircraft and travel routes for wolves. The 200-mile shoreline is also a favorite wolf travelway.

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

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