The Nature of Things
Standing tall

Noble. Majestic.

As I rounded the corner on Mulholland Highway, a male mule deer (Odocoileus hemionus) crested the knoll, neck thickened, muscles fully developed, dark sheen to his coat and an enormously conspicuous set of antlers.

As the deer stood alone on the top of the hill surveying his land, I knew how this creature had become a symbol for virility and potency. He was the essence of true masculinity.

Several days later I watched a different buck, not quite as impressive, closely follow a female grazing on the dried hillsides. He tailed her closely, never letting her fully out of his sight. She seemed to tolerate this behavior, resigned to the fact that rutting season had begun.

Not only would she and every other doe in the Santa Monica Mountains be hounded, every male deer would be engaging in deliberate shows of fitness and dominance. The season of reproduction has begun.

Mule deer or black-tailed deer, depending on locality, are part of the order Artiodactyla. Animals in this order are even-toed, hoofed mammals with effective digestive systems that allow them to eat tough cellulose. Wild animals in this order native to California are deer, elk, pronghorn antelope and mountain sheep. Interestingly, each of these animals has developed the secondary sexual characteristic of horns or antlers.

Antlers or horns?

Bighorn sheep and pronghorn antelope both grow horns. Horns are permanent, unbranched, hollow structures that grow continually throughout the life of the animal. Although hollow, they rest on a bony core with a base rich in blood vessels.

The horn is made of keratin, similar to our fingernails. Upward growth occurs from the base, and new growth is often darker and shinier. If damaged or broken, the horn is unable to be replaced.

Unlike antlers, horns are found on both males and females of these species but are often more elaborate and larger in males. The pronghorn antelope is unique in that it will shed its horns once a year. No other horned animal sheds its horns.

Strikingly different to horns are antlers. Antlers belong to the family of mammals called Cervidae, of which mule deer belong. With the exception of caribou, only male cervids have antlers, which are shed annually.

Simply defined, antlers are temporary, solid, branched, bony structures. But the process of antler growth is not so simple.

Beginning in spring, antler growth is stimulated by the increasing hours of daylight, which cause the pituitary gland to release a growth hormone known as IGF (insulin-like growth factor).

Covered in a "skin" rich with blood vessels and nerves, antlegrowth begins on the pedicles, two

circular areas on the frontal boneof a buck's skull. This stage ogrowth is often referred to as the

velvet stage. During this time the antlers are soft and filled with blood vessels, nervous tissue and cartilage.

Growth may continue through September, but as daylight decreases the pituitary gland indirectly increases the level of testosterone. In response, the antlerharden through calcification andor ossification, where the soft tissue becomes bone by deposition of minerals into the antler matrixThe velvet then dries up, no longer delivers nutrients and sloughs offBy fall rutting season, the antlers are hard, polished, sharp weapons used for dominance and sexual attraction. By late December testosterone levels decrease and the strong union between the antlers and pedicles weakens so that the antlers may be shed. Once shed, skin grows over the remaining wound and the process begins again the following spring.

Marvel of nature

Beyond the magnificent display this process brings to the buck, antler growth is truly a marvel of nature. Antler tissue is one of the fastest growing tissues in the worldgrowing up to 1 inch per day.

To sustain this enormous growth, the buck must be at the height of fitness, not only to ingest enough minerals to grow such a rack but also because of the temporary osteoporosis he undergoes while antlers are growing. During peak growth, the thyroid gland releases calcitonin, a hormone which allows the deer's physiology to "steal" minerals

from its own skeletal structure fothe antlers. The bones hit hardesare the ribs and shoulder blades. Ihas been shown that some deelose as much as 40 percent of theicalcium content during this periodsupporting studies that find deer to

be in an almost constant state oskeleton rebuilding. Miraculously though, by September, assuming the buck is fit, all minerals have been replaced.

Understanding this process better has brought new respect for that regal buck on the hillside. Not only did he stand impressive for the moment, he had survived the trials of antler growth, summer drought, fire season, foraging competition and rut—certainly a good reason to be chosen for future generations.

Meghan Walla-Murphy can be reached at the following e-mail: mwallamurphy@yahoo.com.