The deer family (Cervidae) is a diverse group of mammals that includes species like the white-tailed deer, moose, and elk. The defining characteristic of nearly all members is the presence of antlers, unique structures made of bone. Antlers grow from a permanent bony base on the skull called a pedicle and are shed and regrown annually. This annual renewal distinguishes them from horns, which are permanent structures found on animals like cattle and goats.
Sex Differences in Antler Growth
In most species of the deer family, only the males (bucks, bulls, or stags) grow antlers. The development of these bone structures is directly regulated by the animal’s hormonal cycle. Growth, hardening, and eventual shedding are tied to the seasonal fluctuation of the male sex hormone, testosterone.
Antlers are an outward display of fitness and are primarily used during the breeding season, or rut. Males use their hardened antlers for sparring and fighting with competitors to establish dominance and secure mating opportunities. This competition ensures that the strongest males, capable of growing large antlers, pass on their genes.
The Caribou Exception
The Caribou, known in Europe as the Reindeer, is the major exception to the “males only” rule in the Cervidae family. Both male and female Caribou grow antlers, though the female’s (cow’s) antlers are generally smaller and more slender than the bull’s.
Female Caribou retain their antlers throughout the winter, often shedding them only after giving birth in the spring. This retention is an adaptation for survival in harsh Arctic environments. Females use their antlers to defend foraging sites in deep snow from competitors, which is necessary when pregnant and requiring consistent access to food.
The Annual Cycle of Antler Development
Growth of a new set of antlers begins shortly after the old ones are shed, typically in the late spring. This tissue is among the fastest growing in the animal kingdom. The developing bone is encased in “velvet,” a highly vascularized layer of skin and soft fur. The velvet contains a rich network of blood vessels and nerves that supply the protein and minerals, such as calcium and phosphorus, needed for rapid bone construction.
During the peak growing period, the antlers can grow up to an inch per day in larger species like elk. As the breeding season approaches, triggered by changing daylight hours and increased testosterone, the blood supply to the velvet is restricted. The velvet dries out, cracks, and is rubbed off by the deer thrashing its head against trees and brush.
Once the velvet is removed, the antlers are fully hardened and mineralized bone, ready for the rut. After the breeding season concludes, usually in late winter, the level of testosterone drops. This hormonal change signals the body to begin the process of shedding the antlers. Specialized cells called osteoclasts de-mineralize the bone at the pedicle, creating a weak point known as an abscission line. The loosened antler eventually falls off, completing the annual cycle.