Predators and prey affected by warming

Wolves were up and moose were down in the spring of 2004 at Isle Royale National Park, the home of a 46-year study of predators and their prey. Researchers suspect that a global warming trend may be behind the shift. The moose population slid to 750 on this Lake Superior wilderness island park, down from 900 in 2003 and 1,100 in 2002. In the meantime, the number of wolves has seesawed upward over the past decade, and now stands at 29, as many as the park has seen since 1980 and 11 more than in 2003.

What is bad for moose has been good for wolves, and moose thoughout North America have been hit hard by warmer temperatures that began in 1998 with El Nino and never let up, according to professor Rolf Peterson of Michigan Technological University, Houghton, who has led this study for 34 years.

"What we think is happening is that wolves are cashing in on moose vulnerability that's been induced by a warmer climate," Peterson says. The moose population has been stressed by higher temperatures, particularly the drought of 1998 and then the warm fall of 2001. "Moose can't feed in the summertime if it's too hot. They have a big for coat on, and they can't sweat. They just sit in the shade or in the water."

When moose fail to eat enough in the summer, they can become sickly, weak, and easy prey for wolves during the winter. Moreover, heat precipitates another blight for the big herbivores: ticks. "Warm weather in spring and fair leads to ticks the following winter, and ticks can kill moose."

A single moose can be host to tens of thousands at a time, several per square inch, and each tick can suck up about a cubic centimeter of blood. Rather than browse, the moose scratch themselves against trees or bite their hair out trying to remove the parasites. Weight and blood loss often prove such a handicap that the moose do not survive.

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