Horses are social animals that under feral conditions (or on pasture) live in bands (harems) that consist of several mares, their offspring up to 2–3 yr of age, and at least 1 and as many as 6 adult males. The core of the group is the mares, which stay together even if the stallion leaves or dies. The group size ranges from 2 to 21 horses; multiple-male bands are larger than single-male bands. Groups are not limited to a specific geographic area and will travel in search of resources. Colts and fillies leave the group usually before 2 yr of age (when they become sexually mature), stay alone for a few months, and then join a different group or establish a new one. Some colts may form a “bachelor band” with up to 16 males, and later join other groups in which the stallion has died or been chased away.