Deer are successful herbivorous mammals that originally spread out from Europe to all other continents, except Australasia and Antarctica. There are many different species of deer that can not inter-breed, each with their own specialized adaptations. According to the Encyclopedia Brittanica, deer species often have similar food sources, but adaptations for predator evasion tend to be divergent.
Males in all species except for the Chinese water deer have antlers. The only female species to have antlers are reindeer or caribou. Antlers are grown in spring preparation for the mating season and are considered highly exaggerated secondary sexual traits. They are covered in a layer of "velvet" during formation, which is highly vascular tissue. This supplies oxygen to the structure growing beneath. Before the mating season, calcification results in the antlers becoming hard bone.
Deer are commonly brown or tan, with some species displaying piebald coloring. Piebald deer are brown with white spots or patterns, such as the chital deer found in wooded parts of Asia. Their coloring camouflages them with their environment so that it is harder for predators to see them. When alerted, some deer might freeze and use their camouflage to evade detection. If discovered, species that are adapted to living in woods and thickets may flee in rapid leaps.
White tailed deer are native to the United States, Central and South America. The white tailed deer uses its white tail and neck to communicate danger to other deer in the surrounding area. When alerted, a deer will hold its head high and flash its tail, exposing white coloring which is recognized by others as an alert signal.
Some deer communicate by stomping their feet on the ground or barking when alarmed. This serves a dual purpose of alerting other deer of danger and warning a predator or human to back away.
Like many predated animals, deer have eyes located on the side of their heads. This allows them to have a large field of vision so that approaching predators can be more easily spotted. In addition, large maneuverable ears give deer excellent hearing, and allow them to focus in on quiet noises in one direction, helping them to evade predators.