 Female moose (called "cows") have been spotted on nearby smaller islands, around the main island of Isle Royale, because they swim across to give birth.This allows for them to give birth and raise their young without the threat of wolves preying on their young when they are vulnerable.This also causes trouble for moose that are born in the winter, because they can no longer swim across the water to another island, and must raise the new calf in the snow.