National Geographic : 2004 Oct
P LAY O R P RED AT IO N? Hunting ringed seal pups born in small caves under the snow in Norway's Svalbard archipelago, a fox rears up (opposite top), jumps on a den (mid dle), and dives in headfirst (bottom). Pups often escape from the den into open water. The foxes' keen noses can detect such lairs more than a mile away. Near Hudson Bay, foxes tag along with polar bears in winter (below) to scavenge leftover seal carcasses. Arctic foxes' most vital food source-or lack thereof-is a little fur ball called the lemming. Problem is, the rodents aren't reliable. "They don't commit mass suicide: That's a myth popularized by an old Walt Disney film," says James D. Roth, an ecol ogist at the University of Central Florida who has studied Hudson Bay foxes. "But lemmings do follow a natural boom-and-bust cycle. About every four years they're super-abundant, then they crash for one year, and gradually increase until the next peak." With a circumpolar range (map), arctic foxes probably total several hundred thousand, with wide fluctuations because of variations in the lemming populations.