Gray wolves (Canis lupus) are the largest member of the canine family and are well suited to Yellowstone, where winters are long and severe. They move easily over snow on their large paws, their thick fur keeps them warm, and they have bushy tails, short rounded ears, and long legs that allow them to run 43 miles per hour. Howling is a form of communication often heard on a calm Yellowstone night. Most wolves are social animals that live in packs of five or more members, hunting, eating, and resting together under the leadership of an alpha pair, one male and one female. Pups are born in April or May in a den, and while their parents hunt, other pack members take turns babysitting them as the young wolves learn important skills through play. Wolves’ speed, stamina, and teamwork help them hunt across great distances, and in Yellowstone their primary food is elk, though they also hunt large mammals such as moose or bison and eat small mammals, birds, eggs, berries, and carrion.