Polar bears walk, at an average speed of five to six kilometers per hour, more often than they run. Females with small cubs slow their speed to two and a half to four kilometers per hour.

Polar bears are well known for their slow, plodding gait. Though able to gallop as fast as a horse for a short distance, they prefer a leisurely amble to a brisk pace.

According to a study by Norwegian scientist Nils Oritsland, polar bears expend more than twice the energy used by most other mammals when walking or running. This is probably due to the polar bear's bulky body.

The energy required to chase down prey explains the polar bear's preference for still-hunting. A resting bear expends 13 times less energy than a walking bear — and much less than a running bear.

Polar bears rarely charge after snow geese when walking through a colony. Canadian scientist Nick Lunn believes that the numbers show why: for a dash lasting longer than 12 seconds, the calories spent on the chase would exceed those gained by a catch.

Polar bears can run as fast as 40 kilometers per hour, but only for short distances. They are so well padded with fat that they quickly overheat, even in cold weather.

Younger, leaner bears are the best runners. They can cover two kilometers without stopping. Older, larger bears, however, quickly become too hot.

To appreciate the polar bear's problem, says Canadian scientist Ian Stirling, try putting on your heaviest winter clothing and climbing a steep hill on a hot summer day.

Sources: Hinterland Who's Who, Canadian Wildlife Service, Environment Canada, 1999; Polar Bear by Downs Mattthews (Chronicle Books: San Francisco, 1993); Polar Bears by Nikita Ovsyanikov (Voyageur Press, Stillwater, Minnesota, 1998); Polar Bears by Ian Stirling (University of Michigan Press, Ann Arbor, Michigan, 1988).