Antlers are bony, branching structures that protrude from the heads of male deer and related species, such as elk, moose, and caribou. They are typically shed and regrown annually, and are used primarily for display during mating season, as well as for combat and defense against predators. Antlers are made of bone and are covered with a layer of skin called velvet while they are growing. Once the antlers have reached their full size, the velvet dries up and the animal rubs it off, leaving behind the hard, bony antlers. Antlers can vary in size and shape depending on the species of animal and its age and health.