Global Warming and the Future of Isle Royale

A bull moose wades in the water at Isle Royale National Park. [Photo by Jim Scurlock,  a winner in Lake Superior Magazine’s 1998 photo contest]

You don’t have to look for polar bears in Greenland to find the impact of global warming on wildlife. Climate change now threatens the dynamic balancing act between moose and wolves at Isle Royale, the largest island in Lake Superior and one of the least-visited U.S. national parks. According to the Washington Post:

Researchers monitor both populations by plane overflights early in the year. This spring, they counted 23 wolves and about 650 moose, down sharply from the highs of 50 wolves in 1980 and almost 2,500 moose in 1995. In 2006, moose numbers hit a record low of 385.

With the exception so far of this year, summers over the last decade have been unseasonably warm on Isle Royale. Moose thrive in frigid boreal climates, but when the mercury rises above 60 degrees Fahrenheit, their heart and respiration rates increase, and every step is an effort. They spend warm days resting or submerged in water rather than eating the 40 pounds of vegetation a day they need to fatten up for the winter, when the only food sources are twigs and fir trees.

A hot summer means weaker and older moose may die from heat stress. Come next winter and spring, many others will starve because they ate too little during summer. Or they will be so weak, they will be easy prey for the wolves.

“It all started in 1998,” said study director Rolf Peterson, a research professor at Michigan Technological University. “Moose were dropping dead of starvation right in front of park visitors.”

The heat also encourages ticks that make moose miserable. Later onset of winter means more time for the blood-sucking ticks to latch onto a moose, and earlier springs mean more success for tick eggs.

Over the winter, a tick-infested moose may need to replace 100 percent of its blood. They also rub, bite and scratch off their hair in an effort to rid themselves of the insects. This spring, said study co-director John Vucetich, the average moose had lost 75 percent of its hair, and one in four had lost 95 percent.

“There were bare-naked moose running around,” he said.

No one thinks the moose, which arrived on Isle Royale about 100 years ago by swimming from the mainland, will disappear. But with fewer moose, the wolves could be doomed. Desperate wolves have been seen chomping on old moose bones and even eating green apples from trees. Read more.

Ever since I heard about this story last week on Michigan Radio’s Environment Report, Isle Royale has been on my mind. I’ve been canoing and writing about the island for years (see the essay about Brendan the Navigator), and now it’s time to turn my blog attention in that direction.

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