These large animals live a duality of sorts. On land they are lethargic and clumsy, but in the water they are graceful and quite dynamic. Unlike the fur seal, the walrus is very gregarious and usually rests in large herds. These animals can be seen along portions of the northern coast of Canada where they remain until freezeover occurs. When winter hits, the walrus will migrate southward and overwinter in California and Mexico. The bulls are much larger than the cows. An adult male may weigh up to one-and-a-half tonnes when mature. During the breeding season the bulls form large harems of females which they diligently protect. Should one male invade another's territory a bloody battle is sure to follow. Walrus's feed primarily on fish and invertebrates and are prey for killer whales, large sharks, and humans.