Just one night each year, nine tiny magic reindeer pull Santa and his toy-filled sleigh around the world. They are Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner, Blitzen and Rudolph, and it’s said that these mythical animals are the only reindeer that can fly. Dr. Perry Barboza is a physiologist at the Institute of Arctic Biology, University of Alaska at Fairbanks, who studies reindeer and their closest cousins, caribou. He points to the fact that male reindeer shed their thick antlers at the end of mating season in early December. The females also have antlers, but their thinner version stays with them throughout the winter. This means that Rudolph and Santa's team are all females. What about the non-magical reindeer, the ones which don't fly? At the start of winter, females may be as much as 50% body fat. The fat, which can be a couple of inches thick on their rumps, insulates them from months of cold -- as low as minus 45° F. Males go into winter with much lower fat stores than females, as low as 5%, because they use so much energy during the fall mating season. So, losing the weight of their antlers is probably an energy saver. Reindeer have specially designed coats with hollow hairs that help maintain body heat.