The World of Polar Bears

Adaptations for an Aquatic Environment

A. Swimming

1. Polar bears are strong swimmers; they swim across bays or wide leads without hesitation. They can swim for several hours at a time over long distances. They’ve been tracked swimming continuously for 100 km (62 mi.) (Stirling, 1988).
2. A polar bear’s front paws propel them through the water dog-paddle style. The hind feet and legs are held flat and are used as rudders.
3. A thick layer of blubber (fat), up to 11 cm (4.3 in.) thick, keeps the polar bear warm while swimming in cold water (Stirling, 1988).
4. Polar bears can obtain a swimming speed of 10 kph (6.2 mph) (Stirling, 1988).
5. The hair of a polar bear easily shakes free of water and any ice that may form after swimming.
6. A polar bear’s nostrils close when under water.

B. Diving

1. Polar bears make shallow dives when stalking prey, navigating ice floes, or searching for kelp.
2. Polar bears usually swim under water at depths of only about 3 to 4.5 m (9.8-14.8 ft.). They can remain submerged for as long as two minutes (Domico, 1988).
3. No one knows how deep a polar bear can dive. One researcher estimates that polar bears dive no deeper than 6 m (20 ft.).

C. Thermoregulation

1. Body temperature, which is normally 37C (98.6F), is maintained through a thick layer of fur, a tough hide, and an insulating layer of blubber. This excellent insulation keeps a polar bear warm even when air temperatures drop to -37C (-34F) (Stirling, 1988).
2. Overheating.
   a. Polar bears are so well insulated they tend to overheat.
   b. Polar bears move slowly and rest often to avoid overheating.
   c. Excess heat is released from the body through areas where fur is absent or blood vessels are close to the skin. These areas include the muzzle, nose, ears, footpads, inner thighs, and shoulders.
   d. Polar bears will also swim to cool down on warm days or after physical activity.