Wildlife On The Move

This past June, long-time forester and Executive Director of the Michigan Forest Association, Bill Botti, found two road-killed porcupines near his tree farm in Eaton County (Southwest of Lansing).  That’s about 80 miles farther south than the slow-moving, quill-backed rodents are usually found.  I found a road-killed porcupine in Central Saginaw County on July 30, 2009.  I’ve lived in Saginaw County most of my life and had never seen one before.  Saginaw County, like Eaton County, is far south of the range of this animal.  Porcupines are common in the forests north of a line from Muskegon to Standish, but don’t wander much.  So, the three found dead along the roads may represent a range expansion.  

Porcupines in the East are closely associated with fairly-large mixed forests so any movement of the animals south probably is linked to regrowth of the forests of Southern Michigan.  Bears and bobcats are among other forest wildlife gradually moving into Southern Michigan after being nearly eliminated for more than a century.  

Other Michigan wildlife species are expanding their ranges northward.  A recent study by University of Michigan researchers found that four species—the white-footed mouse, southern flying squirrel, eastern chipmunk, and opossum—are on the increase in Northern Michigan.  The researchers ruled out logging-related changes in forest patterns and land development as causes, concluding that climate change is at the root.  Weather data since 1970 from 16 Upper Peninsula stations showed steady increases in temperatures during the same time the animals expanded their ranges northward.  The researchers found that five mammal species—woodland deer mouse, southern red-backed vole, northern flying squirrel, woodland jumping mouse, and least chipmunk—are declining in their traditional northern Michigan habitats.  Whether it’s getting too warm for them or they are being displaced by the species expanding northward is unclear.  

Meanwhile, bird researchers are noting shifts northward in a wide variety of species.  The Audubon Society released a study in February 2009 based on the organization’s Christmas Bird Counts that take place every winter.  It found that more than half of the 305 North American bird species are wintering at least 35 miles farther north than they did in 1970.  The great diversity of the bird species that exhibited this trend strongly suggest that temperature increases caused the shifts.  However, about one-fourth of all migrating species moved farther south, indicating that not all range expansions are linked to climate change.  

Michigan animals have expanded their ranges in the past due to climate changes.  For example, a warming trend from about 3,000 – 1,500 BC allowed the Blanding’s turtle and other animals associated with warmer climates to extend well north of their ranges.  We also know that these expansions resulted in changes in predator-prey relationships, distribution of seeds, and a host of other impacts.  Scientists are trying to determine if such changes are occurring now, but the research is very difficult because of the complexity of animal-habitat relationships.  

Dr. Patrick J. Rusz
Director of Wildlife Programs

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