The reason is pretty straightforward: Only female reindeer have antlers in wintertime.
"Reindeer — here we call them caribou — are one of the few species of Cervidae where the males and females both have antlers," explained Andrew Hebda, the zoologist at the Nova Scotia Museum.
"Once [the males] finish breeding the antlers fall off and they regrow them."
Females, on the other hand, keep their antlers until they give birth in the spring.
"So if you come across a reindeer with antlers this time of year, it’s female," said Hebda.