Caribou, also known as reindeer, are a species of deer found across the Arctic and sub-Arctic regions of the world. Like all members of the deer family (Cervidae), caribou annually grow and shed their headgear. They are unique among cervids because both males and females typically grow antlers. This annual cycle of growth and loss is a significant biological investment tied directly to their reproductive and survival strategies.
The Biological Process of Antler Shedding
The process of antler shedding is an annual event controlled by hormonal shifts. Antlers are composed of true bone and grow from permanent bony structures on the skull called pedicles. During the summer growth phase, they are covered in velvet, a highly vascularized skin that supplies necessary nutrients and calcium.
As the breeding season approaches, the antlers fully mineralize and harden, causing the velvet to dry up and be rubbed off. Shedding is triggered by a sharp decline in testosterone after the autumn rut. This hormonal drop initiates a process where specialized bone cells, called osteoclasts, resorb bone material at the junction between the antler base and the pedicle.
This targeted bone weakening creates a fracture line, ultimately detaching the antler from the skull, often rapidly. The animal immediately begins the regeneration cycle for the following year.
Seasonal Differences in Male and Female Antler Loss
The timing of antler shedding differs significantly between the sexes, linked closely to their reproductive cycles. Males (bulls) experience a dramatic drop in testosterone immediately following the rut in autumn. Consequently, most mature males shed their large antlers relatively early, typically in late fall or early winter, around November.
Younger males may retain their smaller antlers until later in the winter or even into April. For several months, adult male caribou often remain without their headgear, relying on stored body fat to survive the deepest parts of winter.
Female caribou (cows) retain their antlers much longer than males, providing a distinct survival advantage. Pregnant females keep their antlers throughout the entire winter season, shedding them only shortly after giving birth in the late spring or early summer.
This extended retention provides an evolutionary benefit during harsh, resource-scarce winter months. The pregnant female needs to maximize nutritional intake to support the developing fetus, and her antlers allow her to establish dominance over antlerless males and other herd members. Barren cows shed their antlers earlier than pregnant cows but still later than males, often in the late winter or early spring.
Primary Functions of Caribou Antlers
The antlers serve multiple functions for both sexes throughout the year they are retained. For males, the antlers are primarily a display of health and fitness, used to establish a dominance hierarchy. During the autumn rut, males engage in sparring matches to challenge rivals and secure access to females for mating.
For both sexes, antlers are used for accessing winter food resources. Caribou use their broad antlers to scrape away snow and ice, a behavior known as “cratering,” to reach buried lichens and vegetation. This ability to uncover forage is particularly important for pregnant females, who rely on their retained antlers to defend their feeding craters from other caribou. Antlers provide a higher social status during the winter, ensuring better access to limited food and increasing the likelihood of survival for the pregnant cow and her calf.