Both deer and reindeer are Cervids, which means they are hoofed mammals in the same family but slightly different (though related) species. Reindeer—also called “caribou”—are the second-biggest species of deer (moose are the largest). The chief difference between deer and reindeer is that reindeer have adapted to cold, circumpolar climates, such as Arctic, Nordic, and boreal forests, while white-tailed and other species of “regular” deer prefer more moderate climates. Furthermore, both male and female reindeer grow antlers, whereas in most other deer species only the males grow antlers.