A hibernating bear might appear to be the perfect metaphor for laziness, laying around half the year in carefree slumber. But in fact, it is a marvel of efficiency. New research in the journal Science shows that bears can drop their metabolic rate all the way down to 25 percent of normal while losing only about 10 degrees in body temperature.
Øivind Tøien and colleagues got lucky when a few black bears came a little too close to residents of Alaska for the Alaskans’ comfort. The state’s Department of Fish and Game intended to remove them as a “nuisance,” so the researchers got their hands on the bears and did a little hibernation experiment. They built artificial dens for the large mammals, complete with cameras and observational equipment including radio transmitters, allowing them to track the bears’ body temperatures and other vitals.
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. [National Geographic]
The fact that bears were so much more efficient than other hibernators came as a big surprise, Tøien says:
Up north in the Canadian province of Manitoba, polar bears are receiving some unwelcome guests. Researchers have seen grizzly bears moving into the area for the first time, and that might not be good news for the already-troubled polar bears.
Linda Gormezano and her team, who are publishing the study (pdf) in Canadian Field-Naturalist, weren’t even looking for grizzlies when they started to spot the huge mammals; they were flying around counting fox dens. Before 1996, there was no evidence that grizzly bears encroached on polar bear territory. From that year on, however, there have been at least 12 sightings, negating the prior theory that the barren landscape north of the Hudson Bay was impassable, in terms of resources, for migrating grizzly bears [Discovery News]. If grizzlies can survive there, Gormezano says, they’ll probably want to stay, because there’s a bevy of caribou, fish, and other good things to eat.