Antlers, impressive bony structures found on the heads of deer, are often associated exclusively with male deer. This common perception holds true for most deer species worldwide. However, the world of deer biology reveals exceptions to this general rule.
The Usual Antler Bearers
Antlers are unique to the deer family (Cervidae), differentiating them from horns which are permanent structures found on other animals like cattle. These growths are extensions of a deer’s skull, composed of bone, cartilage, fibrous tissue, nerves, and blood vessels. Each year, male deer, often called bucks or stags, undergo a cycle of shedding and regrowing their antlers.
Antler growth begins from specialized attachment points on the skull called pedicles. During their rapid development in spring and summer, the antlers are covered by a soft, fuzzy skin known as velvet, which supplies oxygen and nutrients. Once the antlers reach their full size and harden, the velvet dries and is rubbed off, revealing the solid bone beneath. This annual cycle is primarily regulated by seasonal changes in daylight and corresponding hormonal shifts.
When Females Grow Antlers
The most notable exception to the rule of only male deer having antlers is the reindeer, known as caribou in North America. Female reindeer develop smaller antlers compared to males, ranging from 9 to 20 inches, while males can reach between 20 to 50 inches.
Female reindeer retain their antlers longer than males, often keeping them through the winter until spring after they give birth. This extended retention provides them with an advantage, allowing them to effectively dig through snow to access food and defend foraging areas during the harsh winter months. Hormonal mechanisms are thought to induce and maintain the hard antler state in female reindeer, aligning their antler cycle with their reproductive needs.
Beyond reindeer, instances of antler growth in female deer of other species are rare occurrences. These cases are linked to hormonal imbalances, particularly elevated testosterone levels. Such antlers are underdeveloped, appearing small, thin, or unbranched, and may even remain permanently in velvet. These unusual growths can also be associated with reproductive abnormalities, such as hermaphroditism.
Why Deer Develop Antlers
Antlers primarily serve as tools for competition and display among male deer. During the breeding season, known as the rut, males use their antlers to establish dominance and compete for access to females. These bony structures act as weapons in physical battles, where bucks lock antlers and push to assert dominance. The size and complexity of a male’s antlers can also communicate his age, health, and genetic quality to other males and potential mates.
Antlers can function as visual signals, allowing males to display dominance and potentially deter rivals without engaging in direct physical confrontation. While they can offer some defense against predators, this is considered a secondary use and not the primary evolutionary driver, as female deer in most species do not possess them. The annual growth of these large bony structures requires a considerable expenditure of energy and resources from the deer’s body.