Walrus: Odobenidae

Walruses socialize in groups called herds, although males and females keep to their groups except when mating in the winter. They travel and forage together in small groups, and several hundred may haul out on ice floes. Thousands of walruses congregate on beaches to molt, shed, or rest. They typically lie close together, oftentimes draped over one another. However, they can annoy one another, at which point they hit their neighbors with their tusks. Sometimes fighting occurs. However, walruses are supportive of one another. They will help a neighbor who is being attacked by a polar bear or attempt to get a dead animal off an ice floe into the water to get it away from a hunter.

Walruses follow the pack ice throughout the year. In spring, they migrate north toward the Arctic Ocean to feed. Males haul out onto beaches along the Alaskan and Russian coasts to molt and rest, while females migrate farther north. Females give birth on pack ice in the spring and summer. Unlike other pinnipeds, walruses do not mate right after giving birth.

In the fall, they follow expanding pack ice, this time heading south. In the winter, males follow herds of females and their young at sea. When the mother-offspring groups haul up on ice floes, the males remain in the water close by. The males go through a courtship display of producing bell-like sounds underwater, followed by whistles and teeth-clacking above the water. The males also fight for dominance, and only the winner will mate with the females of a certain herd. Mating occurs underwater, after which males rejoin their all-male group. This yearly migration north and south covers about 2,000 miles (3,000 kilometers), with walruses swimming or riding on moving ice.

Walruses spend about two-thirds of their lives in the water. They are slow swimmers, typically going up to 4.3 miles (7 kilometers) per hour, but can reach a speed of up to 22 miles (35 kilometers) per hour. They can stay underwater for 25 minutes, although they usually remain underwater for just 10 minutes because they forage on shallow ocean floors.

Pregnancy lasts fifteen months due to delayed implantation, during which the fertilized egg grows a little then waits four to five months before attaching to the uterus for further development. A single calf is born during the spring migration north. Nursing usually occurs in water, with the calf hanging upside down. The calf can swim at birth. Calves remain with their mothers for two years, although they forage for other food before being completely weaned from their mother's milk. Young females stay with female herds, while young males leave to join all-male herds. The long nursing period means that females do not give birth annually. Mothers are very protective of their young, fighting off intruders with their tusks. They carry their newborn on their back in the water. On land, they hold their calf close to their body with their front flippers when they perceive danger. Walruses have been known to guard one another's young and to adopt orphans.