The North American mammals generally slumber about five to seven months without eating, drinking, urinating, or defecating, and then emerge from their dens in the spring none the worse for wear.

Scientists have long known that to survive this lengthy fast, the bears drop their metabolism, the chemical process that converts food to energy.

But it was thought that, like most animals, the bears would have to drop their body temperatures to put the brakes on metabolism—each 18-degree Fahrenheit (10-degree Celsius) drop in temperature should equal a 50-percent reduction in the chemical activity.

Not so, according to the new study. A black bear in Alaska can lower its temperature—generally about 91 degrees Fahrenheit (33 degrees Celsius)—by only about