The Three-Minute Outdoorsman: Wild Science from Magnetic Deer to Mumbling Carp

7. Isn't It Obvious Why Deer Have Antlers?

A L L T H I N G S D E E R 35 bone, velvet and its blood supply are needed and cannot be easily reestablished on a “dead” antler. Maybe peace in the herd is not easily attained if antlers are always visible. Nonetheless, antler regeneration offers some intriguing glimpses into our own biology that may someday have major medical ramifications. 7 isn’t it obvious why deer have antlers? Antlers are bony structures, distinct from horns, unique to deer, and carried by the males of all species except the Chinese water deer and the musk deer, and by both male and female caribou. I wager that most people have a decent idea of the function of antlers on deer: fighting. However, there have been some interesting , if not bizarre, alternative suggestions. In 1937, the German zoologist Han Krieg suggested that deer grew antlers to remove excessive minerals consumed in their diet. Others figured that excreting excess minerals in feces or urine was more likely. In the prestigious journal Nature, Bernard Stonehouse noted in 1968 that growing antlers have a large number of blood vessels, no fat under the velvet, and a large surface area. He suggested that “thermoregulation may thus be the function which primarily determines the form and proportions of antlers, and necessitates their annual renewal.” In other words, he thought that antlers might help deer regulate their body temperature, like ears do on an elephant. Of course if that’s true, why don’t females have them (they do in caribou)? Stonehouse argued that males are usually larger than females and have greater need to cool off in the heat of summer. To put it another way, a male needs to have a big body to be the boss buck, but it carries a summertime “overheating penalty ,” which is circumvented by growing large antlers with velvet that dissipate heat. This idea wasn’t a big hit among deer biologists . t h e t h r e e - m i n u t e o u t d o o r s m a n 36 Even Charles Darwin took a stab at suggesting a function of antlers: predator protection. But others later noted that does and young animals are most vulnerable to predators, and they don’t have antlers. Female caribou, however, might use their antlers to help protect their calves. Some authors have suggested that antlers give bucks better access to food. Caribou use their antlers to expose lichens under the snow, and deer have been seen using their antlers to knock fruit from trees. These uses of antlers are probably secondary, however, because large, elaborate antlers would not be necessary to accomplish these tasks. There was even a study that showed that the antlers of moose serve to redirect sound toward the ears, giving the male moose an added advantage of an external hearing aid! Antlers likely have at least one function. Useless features, especially expensive ones, don’t last long in nature. So having antlers must make the bearers more “fit” and give them an advantage that can be passed on to their offspring. We know, for example, that birdsong helps males to attract mates and to repel other males. Antlers aren’t much different. Use in competition for mates is probably the most obvious function of antlers, and like birdsong, antlers probably function in at least two ways. In particular, they help males to establish who is most dominant, and females prefer the most dominant bucks. It is not straightforward, however. If the size of the antlers was a perfect predictor of a buck’s fighting ability and if bucks could somehow assess whether their rack was smaller than another buck’s, there would be no need for fights. If a buck’s rack was smaller, he would give way to the bigger buck because he would know he would lose the fight and, if injured, be out of action and forfeit any possible chance for a finding mates. Bucks have reason to be around during the rut even if they are not the biggest. A dominant buck may spend twenty-four hours with a doe in heat; during that time less dominant males often take advantage of mating opportunities. Evidence in support of the importance of antlers in fighting A L L T H I N G S D E E R 37 comes from experiments in which...