Reindeer (also called caribou) are native to North America and northern Russia, living in cold conditions. They are part of a group of animals called cervids, or deer; however, they are the only members of this group where both the male and female deer grow antlers! They use these large appendages to fight and establish territories. During the mating season, called a rut, males establish large groups of females that they defend from other male reindeer in the area, utilizing their antlers as a defense.

Art by @Folktailsandfeathers

[Edited by Isabelle McDonald]

Reference:

Butler, H. E., & Geist, V. (1986). Mating strategies of woodland caribou: Rangifer tarandus caribou [PhD dissertation]. University of Calgary.