National Geographic : 2016 Jan
A genteel disquisition on love and lust in the animal kingdom Basic Instincts Obviously, scientific accuracy is important. But did a zoo’s web- site have to upend a beloved Christmas folktale by publishing this sentence: “Rudolph the red-nosed reindeer must have been a female”? Now, now. Compose yourselves. This all can be explained. Rangifer tarandus includes the caribou of North America and the reindeer of Eurasia. Reproductive biologist Peter Flood of the University of Saskatchewan, Canada, says it is the only deer species in which both sexes grow antlers—and in which annual rack-shedding cycles separate the bulls from the cows. In spring both sexes begin to grow antlers that, by fall, harden to bone. Flood says adult males’ antlers are rightly called weap- ons of sex, used to drive off other bulls in rut. Once the cows are pregnant, adult bulls’ testosterone levels drop, triggering a bone cell change that makes their antlers fall off, usually in Novem- ber or December. Young males keep their antlers somewhat longer—but pregnant cows keep their racks all winter and into spring, the better to fend off threats and guard feeding sites. Only after they give birth, typically in April or May, do they shed their antlers (which nonpregnant cows did some weeks earlier). So to give Santa’s sleigh pullers their due, let us clarify. Reindeer still antlered on Christmas Eve may be adolescent males—but could very well be females, and pregnant ones at that. —Patricia Edmonds HABITAT/RANGE Tundra and taiga zones of Eurasia and North America CONSERVATION STATUS Least concern OTHER FACTS Climate warming in Rangifer tarandus’s range causes more melting and re-icing of snow, making it harder for them to dig for food. Her Rack Versus His This female reindeer was photographed at the Miller Park Zoo, Bloomington, Illinois.