Bears also tend to sleep more during the day than at night, although in the summer, with twenty-four hours of light, this does not apply.

Patterns of freeze-up and breakup influence the distribution and number of seals, the polar bear's main prey.

These special characteristics explain its preference for still-hunting (lying motionless beside a seal's breathing hole, waiting for one to surface).

The seals surface more frequently then, so a bear's chance of catching one at a breathing hole is greater after nightfall.

Being active at night may relate to the behavior of seals, which feed at night on various fish that come up closer to the surface.

Seals sleep underwater.