Election Section

Getting Up Close and Personal With the Mule Deer

By JOE EATONSpecial to the Planet
Tuesday June 15, 2004

We don’t get many mule deer in my current neighborhood. But some years back, when I lived in a rickety in-law apartment near the Berkeley Rose Garden, they—along with the raccoons, skunks, and possums—were regulars. They would bed down in the ivy-covered gully below the house, or placidly consume the few things we had managed to grow in the garden (a challenge at best, since it had the kind of drainage you would expect from a former fishpond.) Mostly they were does, sometimes with fawns in tow. Bucks wer e rarer—more circumspect around people, maybe—but a few showed up from time to time. I would admire their racks from a discreet distance, and wonder about the whole antler thing. 

If I were a stickler, I’d call them black-tailed deer—the semi-official mon iker for Odocoileus hemionus columbianus, the Pacific coast subspecies of the mule deer. But I’ve seldom heard that term used around here. Mulies from the Sierra and the Rockies have black-tipped tails and large white rump patches, whereas our coastal rac e has a smaller white patch and an all-black tail. Blacktails also tend to be darker and grayer than interior populations. But they share with all other mule deer the habit of stotting—bounding stiff-legged, with all four feet touching down at once—when alarmed, and the way the antlers branch. 

When you think about it, antlers are among nature’s most extravagant inventions. They started small; the most primitive deer species have modest spikes. But millions of years of evolution have elaborated them into the dichotomous-branching racks of the mule deer, the sweeping tines of the elk, the massive palmate structures of the moose. The extinct Irish elk, not an elk at all but an oversized fallow deer, had to schlep around antlers with a 12-foot span and a wei ght of 90 pounds. 

And the remarkable thing is that deer—mostly male deer, although both sexes of caribou are antlered—have to produce these baroque structures every year. With the exception of the oddball pronghorn, deciduous horns are unique to the dee r family. A bull buffalo or kudu or a bighorn ram wears the same set of horns for life. But a mule deer casts its antlers after the fall rut and grows a new set during the long run-up to the next mating season. Each year’s rack is larger and more impressi ve than the last, at least until old age (if the deer is that lucky) sets in. 

Antler formation is a big deal. Triggered by hormonal surges, growth starts at the bony nubbins called pedicles on the skull’s frontal bone. Cells from both the pedicle and the overlying skin multiply like crazy to make cartiliginous antler tissue, which then hardens to bone. It’s not dead bone, though; antler is laced with nerves and contains pockets of living cells. 

Testosterone is important in pedicle growth, but not in the making of the antler itself; other substances, such as insulin-like growth factor one, are implicated there. The process demands lots of calcium and phosphorus. Some comes from the deer’s skeleton, mostly the ribs; osteoporosis is a byproduct of peak antler growth. But the buck (or stag, or bull) can’t always satisfy the antlers’ mineral requirement by resorbing its own bones. 

The need for extra minerals has led deer to some very undeerlike behavior. Although we like to put animals in neat little boxes labeled “carnivore” and “herbivore,” their actual behavior often defies those categories. Deer sometimes turn predator. On the Scottish island of Rum, red deer have been documented as eating the nestlings of a small seabird, the Manx shearwater. A Midwest ern ornithologist once caught a white-tailed deer eating a warbler that was snagged in his mist-net; others have witnessed whitetail predation on young songbirds. And I remember reading somewhere about calcium-starved deer munching on box turtles. 

Why go to all this trouble, though? Charles Darwin gave some thought to that in the portion of The Descent of Man that is not actually about the descent of man, but about the evolution of secondary sexual characteristics. He acknowledged that antlers could be f ormidable weapons in combat between stags (or bucks, or bulls) for access to females. But they seemed to him to be overdesigned for that. Remember the sets of interlocked deer skulls in the Academy of Science’s recent “Skulls” exhibit, whose owners had be en unable to disengage and had presumably starved to death? Darwin, noting the risk of such fatal entanglements, commented: “The suspicion has therefore crossed my mind that [antlers] may serve partly as ornaments.” 

That suspicion has found support in subsequent research. Antlers, like the lion’s mane and the peacock’s tail, are signage. They signal fighting ability to potential male rivals, and fitness—in the Darwinian sense of the ability to sire lots of healthy fawns—to potential mates. Even in macho species like deer, female choice is important. Big antlers might also signal that a buck is good at metabolizing calcium, a crucial trait to any of his female offspring who will become nursing mothers. And antlers are honest signals. Males of some animal species can make themselves look larger, stronger, more imposing than they really are. But you can’t fake antlers. 

The semiotics of antlers go beyond species boundaries. Humans have been looking at them and thinking “Power” for a long time, at least sinc e that Cro-Magnon artist painted an antlered god or shaman on the wall of Les Trois Freres cave. Every September in the Staffordshire village of Abbots Bromley, costumed men wielding reindeer horns still perform a stately Morris-type dance ending in ritua l horn-to-horn combat. 

The symbolic function of antlers and the high cost of growing them makes sense of the fact that aging bucks have smaller antlers. Their days of dominance are over; their change of signals may exempt them from the young bloods’ challenges while giving their old bones a respite.