Reindeer, or caribou, are Arctic ungulates (Rangifer tarandus) adapted to survive in extreme environments. While known for their cultural ties to winter holidays, their biology is unique. Unlike many other large mammals, the female reindeer exhibits physical and reproductive traits essential for the species’ survival in the harsh North.
Terminology for Female Reindeer
A female reindeer is properly referred to as a cow, following the standard terminology used for many large female ungulates. Although “doe” is sometimes used for female deer, “cow” is the accurate and common designation for Rangifer tarandus. The adult male is called a bull, and the young of either sex is known as a calf. This naming convention helps herders and biologists classify the animals within the herd structure.
The Unique Role of Antlers
Reindeer are the only deer species where both males and females routinely grow antlers. This shared characteristic is a specialized adaptation, as the female’s antler cycle is strategically timed for the severe winter months.
Mature males shed their antlers shortly after the rut, typically in late fall or early December. Females retain theirs throughout the winter, shedding them only in the spring, generally in April or May, just before or after giving birth. This retention gives pregnant females a significant competitive edge during the most nutritionally challenging time of the year.
The female uses her antlers as tools to dig through dense snow layers, a behavior known as cratering. This allows them to access essential lichen and other forage needed to fuel their late-stage pregnancy and maintain energy reserves.
Although functional, female antlers are significantly smaller and less branched than those of the male. Female antlers typically reach about 20 inches, while a mature male’s can measure up to 51 inches. The difference in size is secondary to the timing of retention, which provides temporary dominance over antlerless males in securing winter resources.
Gestation and Calving Biology
The female reindeer’s reproductive cycle is timed so the calf is born during the brief window of maximum resource availability in the Arctic spring. Mating occurs in the fall, and the gestation period lasts approximately seven and a half months, or about 228 days. The range of gestation length can vary from 203 to 240 days, but the majority of births are synchronized, occurring in late spring or early summer, typically across May and June, when forage emerges.
Females usually give birth to a single calf, as twinning is rare. This synchronized timing minimizes losses to predators, as a surge of newborns can overwhelm local populations.
The newborn calf is remarkably precocial, able to stand within an hour of birth and keep pace with the migrating herd within a day. This rapid development is supported by the mother’s milk, which is exceptionally rich. Reindeer milk boasts a fat content of 15 to 20 percent and a protein content of 9 to 10 percent.
This high concentration of fat and protein enables the calf to double its birth weight in as little as two weeks. The high-energy milk fuels the fast growth required for the calf to survive the looming Arctic winter.