According to the Alaska Department of Fish & Game, while both male and female reindeer grow antlers in the summer each year (the only members of the deer family, Cervidae, to have females that do so), male reindeer drop their antlers at the beginning of winter, usually late November to mid December. Female reindeer retain their antlers till after they give birth in the spring. Therefore, according to every historical rendition depicting Santas reindeer, every single one of them, from Rudolph to Blitzen … had to be a girl.

(MMs remark: That could have fooled me; I never saw a reindeer stop to ask for directions …)