This is a buck (male deer) in the process of growing new antlers. Each year, at the end of the mating season, male deer lose their antlers. The following year, at the start of the mating season, they grow new antlers. Antlers are made of bone, and as they are growing, they are covered with a layer of fuzzy skin called velvet. The velvet has lots of blood vessels to nourish the bone as it grows. Once the antlers are fully grown, the velvet dies, and peels away. The bone of the antlers dies too, and they stay in place until the mating season is over, when they fall off.