Reindeer, or caribou, are members of the deer family, Cervidae, and are unique because both males and females typically grow antlers. These bony structures are shed and regrown annually, a cycle synchronized with the changing seasons of their Arctic and sub-Arctic habitats. The specific timing of shedding varies dramatically between the sexes. This annual process of growth and loss serves a foundational role in the reindeer’s survival and social structure.
The Biological Process of Antler Growth and Shedding
Antlers begin their annual growth from permanent bony growths on the skull called pedicles. During the rapid growth phase, the antlers are covered in velvet, a soft, highly vascularized skin. The velvet delivers oxygen and nutrients, allowing the antler to become one of the fastest-growing tissues in the animal kingdom, sometimes growing up to an inch per day.
As the antler nears its full size, the inner structure begins mineralization, transforming the tissue into solid bone. Once hardened, the velvet dries out and is stripped away by the reindeer rubbing its antlers against vegetation. The final stage, casting, is triggered by hormonal changes that cause specialized cells to resorb bone at the base of the pedicle, causing the antler to loosen and eventually detach.
Seasonal Timing Differences Between Males and Females
The precise schedule for antler shedding is directly controlled by sex hormones, leading to significant differences between males and females. Mature male reindeer shed their antlers shortly after the rut, or mating season, due to a sharp drop in testosterone levels. This shedding typically occurs in late autumn, around November or early December, once their reproductive function for the year is complete.
Younger males often retain their antlers for a longer period, sometimes into the winter months, with some shedding as late as April. This delayed shedding is due to lower or less volatile testosterone levels compared to mature bulls. Castrated males also show an altered cycle, retaining their antlers through the winter until April or May, since the lack of testosterone disrupts the normal shedding signal.
Pregnant female reindeer have a fundamentally different cycle, retaining their antlers throughout the entire winter and shedding only after they give birth. Calving usually occurs in the spring, meaning females typically shed their antlers in May or June. Non-pregnant females often shed their antlers earlier, sometimes in April or May.
The retention of antlers gives pregnant females a distinct advantage in the harsh winter environment, often giving them dominance over antlerless males when competing for scarce resources. This unique timing is influenced by hormones like estrogen, which allow them to maintain their antlers when males are already bare.
The Essential Role of Antlers in Reindeer Survival
The annual growth and retention of antlers are directly tied to the reindeer’s survival in its cold habitat. During the autumn rut, male reindeer use their antlers to establish dominance and compete for access to females. The size and condition of the antlers act as an honest signal of the male’s health and strength, which influences mating success.
Beyond mating, antlers are a tool for accessing food during the long, snowy winter months. Both sexes use their antlers to perform a behavior known as “cratering,” which involves scraping through hard-packed snow and ice to uncover lichen and other forage beneath. This ability to dig for food is important for pregnant females, who must maintain their strength for gestation, and their retained antlers allow them to dominate prime feeding spots.
The antlers also play a part in defending against predators and establishing social order within the herd. By retaining their antlers until spring, the pregnant females ensure they have the tools necessary to protect their feeding areas and secure the nutrients needed to support their developing calf. The utility of the antlers shifts seasonally from a reproductive weapon in males to a survival tool in females.