Amateur naturalists made a startling discovery: It’s not salmon or blueberries that fattens up these giant predators for winter.
Right about now, the grizzlies of Yellowstone National Park are starting to think about hibernation. This week or next, as food becomes scarce, they’ll head up into the mountains and hunker down in dens under rocks and trees. They’ll cut their metabolic rate in half, drop their heart rate down to about 18 beats a minute, and take a breath only once every 45 seconds. And they’ll stay like that until springtime.
Many of the park’s bears will be getting by for the winter largely on the energy built up from gorging on moths. That’s right: The largest and most ferocious predator in North America eats fluttery little army cutworm moths (Euxoa auxiliaris).
A grizzly researcher first discovered this strange behavior in 1952. But nobody paid much attention until the mid-1980s, when a radio-collared grizzly bear wandered up to the steep rocky slopes, and researchers started to wonder just what it was doing there.
A couple of amateur naturalists were at the time spending half of every year in the field watching grizzly bears, and they did the first real study of moth-eating behavior. I met Steve and Marilyn French back then and spent some time wandering with them in grizzly habitat, as they studied how grizzlies adapted to every possible food source in their environment, including the moths.
Those kinds of details mattered then because grizzlies in greater Yellowstone were put on the Endangered Species List in 1975. The U.S. Fish and Wildlife Service delisted them in 2007, under pressure from politicians in Wyoming. But a federal judge reinstated protection two years later, and grizzly diet was a critical factor. He noted that the bears depended on nuts from whitebark pine trees, a species that had sharply declined because of tree-killing beetles. Environmental groups are now suing to block the continued FWS effort to delist the species, which could happen as soon as next year. Fewer than 1,000 individual grizzlies survive in the lower 48 states, down from 50,000 in the 19th century.
In the course of their research, Steve and Marilyn French documented how some bears depend on the spawning run of cutthroat trout. That’s another food source that has now almost disappeared, because of illegal introductions of lake trout, which not only eat cutthroats but do their spawning on the lake bottom—meaning no run for the grizzly bears.
The Frenches also documented the quirky nuances of grizzly bear foraging. In springtime, when the weather is wet, for instance, earthworms bunch up for unknown reasons under the park’s tufted hair grass. “And then the bears come and flip over the grass, and thp-thp-thp, it’s like spaghetti,” Steve told me.
Read the rest of this article at http://www.takepart.com/article/2013/11/15/surprising-meal-grizzly-bears-yellowstone-national-park-hibernation