National Park Service U. S. Department of the Interior Isle Royale National Park
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Mammals   
Few Call This Island “Home” Many common mammals found along the shores of Lake Superior are conspicuously absent from Isle Royale. There are no porcupines; bear do not call this place home even though there seems to be suitable habitat for them. Why would this be? 
A Difficult Journey The answer is found in what surrounds Isle Royale – Lake Superior. Any mammals that reach the Island must cross the Lake’s icy waters, a trip of at least 14 miles. Some mammals are better adapted to making such a crossing than others. Bats can fly over. Good swimmers, like moose, may swim to Isle Royale. Mammals that can walk long distances, like the wolves, can cross Lake Superior when (and if) it freezes. Other mammals, like bear, do not swim long distances and are sound asleep through the coldest months. Some mammals, like porcupine stay awake all winter, but would not make such a long journey, especially over mile after mile of nothing but ice. Because reaching Isle Royale is so difficult, even mammals that can make the trip rarely do so. Today, only 18 species of mammals can be found on Isle Royale, compared to more than 40 on the surrounding mainland.
Fewer species means fewer relationships between species. Isle Royale has only one large prey species, the moose, with only one predator, the wolf. This simple ecosystem provides an ideal laboratory for scientists to study and monitor the interactions of these animals.
Uniquely Royale If you ventured to Isle Royale, you probably would not get a glimpse of a wolf and you might not see a moose; but almost certainly you would encounter a red squirrel, scolding you loudly for invading its territory. The red squirrel is the most abundant mammal on Isle Royale. How did a squirrel make the challenging crossing to the Island? No one knows for sure; but these squirrels have been isolated from their relatives for so long that they are now considered a distinct subspecies. A closer look would reveal that the Isle Royale squirrel is smaller and less red than its mainland counterparts, and a careful listener would detect differences in its vocalizations. The scientific subspecies name of this animal, regalis, translates as “regal” or “kingly”, appropriate for this unique Isle Royale resident who behaves as if king of its domain.
The Ever-changing Web These “kings” and other mammals of today’s Isle Royale may be gone tomorrow. Nothing stays the same for very long on an island. A little over a hundred years ago, a survey of the Island’s mammals would have resulted in a list quite different from the present. Wolf and moose would be noticeably absent. Caribou would represent the large prey species while coyote and lynx would serve as the predators. The web of life on Isle Royale is ever-changing. This ecosystem may not be as simple as it first appears. Mammals of Isle Royale
Diurnal – Most active during day Nocturnal – Most active at night Crepuscular – Most active at dawn and dusk _____________________________________________________________________________________
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