Polar bears primarily eat seals. Polar bears often rest silently at a seal's breathing hole in the ice, waiting for a seal in the water to surface. A polar bear may also hunt by swimming beneath the ice. But climate change is making it harder for polar bears to hunt. Ice melts earlier and re-forms later than it has in the past. Without the sea ice, the polar bear must scavenge for other, less nutritious food.

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Polar bears roam the Arctic ice sheets and swim in that region's coastal waters. They are very strong swimmers, and their large front paws, which they use to paddle, are slightly webbed. Some polar bears have been seen swimming hundreds of miles from land—though they probably cover most of that distance by floating on sheets of ice.

In fall pregnant polar bears make dens in earth and snowbanks, where they'll stay through the winter and give birth to one to three cubs. In spring the mother emerges from her den followed by her cubs. During that time she will protect them and teach them how to hunt. The U.S., Canada, Denmark, Norway, and Russia signed an agreement in 1973 to protect polar bears.