The reindeer (caribou in North America) is unique within the deer family because females regularly possess headgear, properly called antlers. The common misconception that only male deer grow antlers is generally true for species like whitetails, elk, and moose, but the reindeer is a biological exception. Both male and female reindeer (Rangifer tarandus) grow and shed these bony structures annually. This shared trait is an adaptation that plays a significant role in the survival of the species in their harsh Arctic and subarctic environments.
Reindeer Are Unique Among Deer Species
In almost every other species belonging to the Cervidae family, the growth of antlers is a characteristic found exclusively in the males. Antler production in species like the white-tailed deer and elk is closely tied to high levels of the male sex hormone testosterone. The antlers serve primarily as weapons for competition between males during the autumn mating season (rut) to establish dominance and secure breeding rights.
The reindeer is the only member of the deer family where females routinely grow antlers, although female antlers are generally smaller and less branched than those of a mature male. While some female deer in other species may rarely grow antlers due to hormonal imbalances, it is a typical trait in female reindeer populations. This biological difference highlights an evolutionary path distinct from their cervid relatives, favoring a survival advantage for both sexes in the extreme northern latitudes they inhabit.
The Timing of Antler Growth and Shedding
The most pronounced difference between male and female reindeer is the timing of their annual shedding cycle. Mature male reindeer shed their antlers relatively early, typically in late autumn or early winter (November or December), right after the intense mating season concludes. The sharp drop in testosterone levels following the rut triggers this shedding process.
Pregnant female reindeer retain their antlers throughout the entire winter season. They do not shed their headgear until the spring (April or May), shortly after giving birth to their calves. This distinction in the shedding schedule means that any reindeer observed with antlers during the mid-winter months is likely a female, a young male, or a castrated male, as the mature bulls are already bare-headed. This difference in timing is linked to the respective needs of each sex during the coldest time of the year.
Why Female Reindeer Retain Antlers
The female reindeer’s ability to retain her antlers through the winter is an adaptation connected to her reproductive state and the need to secure food. During the long, dark winter, pregnant females require access to the best feeding grounds to sustain themselves and their developing calf. They use their antlers to establish dominance and defend feeding craters they dig in the snow to reach lichen and other vegetation.
Antlers allow the pregnant females to outcompete any mature male that has already shed his own, granting them preferential access to scarce winter resources. The antlers also serve as a tool for defense against predators and for maintaining a hierarchy within the herd. This functional advantage ensures that the pregnant females and nursing mothers receive the nutrition necessary for a successful birth and calf survival in the challenging Arctic environment.
Antlers Versus Horns
The question of whether a female reindeer has “horns” involves a misunderstanding of biological terminology, as reindeer possess antlers. Antlers are structures made entirely of bone that grow from bony outgrowths on the skull called pedicles. They are shed and regrown completely new each year, making them one of the fastest-growing tissues in the animal kingdom.
Conversely, true horns are permanent structures never shed during an animal’s lifetime, found on members of the Bovidae family (e.g., cattle, sheep, and goats). Horns consist of a bony core covered by a sheath of keratin, the same substance that makes up human fingernails and hair. The reindeer’s annual cycle of growth and shedding confirms their headgear is classified as antlers, not horns.