Polar bears only rarely catch seals in open water. They are far more successful at hunting them on the sea ice. On the ice, the bears catch their prey when they surface to breathe.

Rifts in the ice, called leads, give seals access to oxygen. Seals also surface to breathe at polynyas, areas of open water surrounded by ice.

Polynyas are created by a combination of winds, tidal currents, and upwellings of water. They remain open throughout the winter months.

In addition to surfacing at leads and polynyas, seals cut breathing holes in the ice. The Inuit call these holes aglus.

In fall, each seal cuts ten to fifteen aglus in the ice, using the sharp claws on their foreflippers. They keep the aglus open throughout the winter, even when the ice is six feet deep.

Seals swim to the surface to breathe every five to fifteen minute. But because they visit as many as fifteen breathing holes, a polar bear's wait for its prey can be long.

Polar bears locate breathing holes with their powerful sense of smell. When a bear finds an aglu, it waits patiently for the seal to surface — which can take hours or days.

Polar bears depend on the presence of ice for access to seals. In summer, when the floes retreat north, polar bears will travel hundreds of miles to maintain contact with their prey.

Between summer and winter the amount of ice-covered water can change rapidly. Polar bears learn to follow the ice to stay with their food source.

Those polar bears that are stranded on land in summer must stay there until the ice forms again in fall. On land, the bears face lean times, for they seldom catch seals without a platform of ice.

Sources: Polar Bears by Ian Stirling (University of Michigan Press, 1988); Polar Dance by Fred Bruemmer (Images of Nature, 1997).