What is the only kind of deer whose females have antlers?

While antlers are typically a male-only feature in the deer family, used for sparring and displaying dominance, there is one notable exception to this rule. In the species known as reindeer, or caribou in North America, both males and females grow a set of antlers each year. For females, this unique adaptation is a crucial tool for survival, not for attracting a mate.

The reason for this difference comes down to the harsh arctic environment and the timing of their life cycle. A pregnant female reindeer must compete for scarce food sources, like lichen buried under the snow, throughout the long winter. Her antlers allow her to defend these feeding craters from others, ensuring she gets enough nutrition for herself and her developing calf.

Interestingly, the males shed their large antlers shortly after the autumn mating season, meaning they are antler-less for most of the winter. Females, however, retain their smaller antlers until after they give birth in the spring. This has led to the popular holiday observation that the famous reindeer pulling Santa's sleigh, always depicted with antlers on Christmas Eve, would almost certainly have to be female.