A Human Shield--for Moose

Joel Berger and moose with bag of scat. Courtesy of Joel Berger

Friday, October 12th, 2007--

Over the last decade, mother moose around Grand Teton National Park, in the Yellowstone ecosystem in Wyoming have been birthing their babies closer and closer to the road, according to a new study in the journal Biology Letters. It may have to do with the bears.

Bears eat moose calves. A 2004 study in Alaska found that ninety percent of moose calf mortality was related to brown bears.

Moose protect themselves from bears by staying away from them. "Moose are very savvy with their noses," says Joel Berger, author on the Grand Teton study and a senior scientist with the Wildlife Conservation Society and the John J. Craighead chair of wildlife and conservation at the University of Montana. "We know from experiments that we've done with wild moose--when we place bear odor out there, in other words poop, scats--moose tend to move away from it."

Berger studied moose mothers for ten years in Grand Teton National Park. In this ecosystem, 90 percent of moose calves are born during a nine-day span each year. "To have a forest-dwelling animal be so synchronous is pretty stunning," Berger says. The births may be synchronized to take advantage of food availability. The other idea is that a moose calf has a better chance of surviving if many other moose calves are born at the same time. "If most of the mothers are popping babies at the same time, it swamps the system," Berger explains.

Given the threat of bears, and moose's demonstrated ability to avoid bear scent, Berger says it seems likely--although he can't be sure--that moose are moving toward the road to avoid the bears.

If indeed that is the reason mother moose are migrating toward roads (non-pregnant moose are not showing this trend), humans are playing an interesting role in shifting the predator-prey dynamic. The study suggests, Berger says, that humans are shielding moose from bears. But a human shield may not work forever. "This just may just be a fleeting phenomena where moose have developed a good strategy," Berger says, "but they may not be able to maintain it because bears are figuring it out."

--Flora Lichtman

Sources

Joel Berger
Senior Scientist with the Wildlife Conservation Society John J. Craighead Chair of Wildlife and Conservation University of Montana Teton Valley, ID