Global Warming Threatens Moose, Wolves

“Humans have made summers increasingly hot, which likely exacerbates moose ticks,” says John Vucetich, a population biologist in Michigan Tech’s School of Forest Resources and Environmental Science. “Both the heat and the ticks are detrimental to moose. If wolves go extinct for a lack of moose, humans will be to blame.”

Isle Royale is an isolated wilderness island near the northwestern shores of Lake Superior, close to the Canadian border. A U.S. National Park, it is home to a variety of rarely seen wildlife, including moose and wolves.

But the moose and wolf populations on Isle Royale are shrinking, and Michigan Tech researchers, who have been them for nearly 50 years, blame it on climate change. Five of the last six summers have been the hottest in half a century.

“Hot summers are hard on moose,” said Vucetich. Hot weather causes moose to rest more and forage less, he explained, and summer foraging is how moose prepare to survive the long, bitter winters.

Warm springs and falls may also promote breeding of winter ticks, a species of tick that feeds on moose. The past five warm years have brought devastating tick infestations to Isle Royale. “The ticks weaken the moose and make them vulnerable to wolves,” Vucetich explained. “The loss of blood caused by the ticks can even kill the moose outright.”

In 2000, there were 1,100 moose on the 210 square mile island. Now there are fewer than 400.

As the numbers of moose dropped, the wolf population initially grew, probably in response to the additional food supply provided by weakened moose. But now the wolves—the moose’s only predator on Isle Royale—are themselves falling prey to the changing climate. Between 2006 and 2007, the number of wolves on the island decreased from 30 to 21.

Again, Vucetich blames the weather. “There are too few moose for the wolves to eat, and the reason there are too few moose is very likely that hot summers and ticks made them too easy for the wolves to kill,” he said.

During the ongoing 50-year study of the wolves and moose on Isle Royale, the populations have never dropped this low. The wolves on the isolated island are the only predator of moose, and moose are virtually the only prey for the wolves. It’s a model ecosystem that may be slipping into a new balance—one that may not include wolves.

“Ecosystems change; that’s normal,” said Vucetich. “When they change quickly in dramatic ways, that creates a new balance,” he explained. “Nature is still in balance. It may just be a balance that doesn’t favor humans and disenfranchises certain kinds of wildlife.”

Scientists believe that wolves first walked to Isle Royale in the mid-20th century, across the 15-mile channel between the island and Canada. That channel used to freeze regularly. It freezes much less frequently now—another sign of climate change. Wildlife experts think that the moose swam across, although it is possible that they were brought on a boat.

“Continued hot summers could mean more trouble for moose, and as a consequence, for wolves on Isle Royale,” Vucetich added.

If the moose or wolves vanish from Isle Royale, “we will have lost one of the best opportunities to study the relationship of predators and prey,” the population biologist said. “And we must study it in order to understand and preserve it.”