When you spot a male deer, the first thing you likely notice is the set of antlers upon his head. These bony growths are one of the most distinguishing and notable characteristics of these mammals – and all animals with antlers, at that. Deer, elk, moose, caribou and nearly all the other members of the Cervidae family grow and shed their antlers on a yearly basis.

To better understand why deer shed their antlers, you should also know what antlers are and why members of the Cervidae family grow them in the first place.

You might have heard the terms ​antler​ and ​horn​ used interchangeably. However, antlers and horns have drastically different makeup and grow on different animals!

Mammals with horns, such as goats, sheep and other members of the Bovidae family, grow a bony core with a layer of blood vessels and a sheath of keratin over top. Horns often grow continuously throughout the animal's life.

Conversely, antlers consist entirely of bone, and the animal sheds and regrows them every year. Nearly all 47 species in the Cervidae family, also known as the deer family, grow antlers. The only exception is the Chinese water deer, which grows elongated canine teeth instead.

All of the various species of animals with antlers grow them for the same reason. Researchers believe the Cervidae family developed antlers as a way to compete with other males and increase their reproductive success. The largest males with the biggest antlers breed with the most females, thus spreading their genes to the next generation.

Antlers also serve these creatures in defense against predators by providing them with a weapon to fight back with. They also use their antlers to assert dominance over other deer for non-reproductive resources as well, such as prime feeding spots.

Nearly all animals with antlers shed those antlers seasonally. But why do they shed their antlers in the first place? Each year, as the deer ages and develops, his antler growth increases. Males must shed their antlers to make room for the growth of the new antler each season. Each year, a male's antlers grow larger than the year before.

The process of antler shedding begins in late winter and early spring. As the days shorten, the males produce less testosterone, and the calcium connecting their antlers to their skull weakens. Eventually, the antler falls off. The process of a deer shedding its antlers is known as ​casting​. In most species, new growth begins shortly after the area forms a scab.

All animals with antlers cast and regrow their headgear annually, typically in association with the breeding season and the length of daylight. However, the specific months that this process occurs vary based on where the species lives geographically. For example, white-tailed deer in North America cast their antlers around February and March, while the European roe deer shed their antlers around November.

The antler growth cycle, regardless of species, consists first of casting the antlers, then regrowing velvet-coated antlers. The antlers then harden and the velvet dries up and falls off. Finally the fully-grown antlers are ready for the new breeding season.

In white-tailed deer, the male drops his antlers in February and March and begins regrowing them slowly in April and May. Once June rolls around, his antler growth increases rapidly, up to two inches per week.

The male's antlers have fully hardened by September and he begins shedding the velvet covering. After about 24 hours of scraping his antlers against various branches and shrubs, the male has removed the velvet and is ready to compete with other males for breeding rights!