HORNY DEER (September 1996)

The deer are getting horny this time of year…or I should say “antlery”. Deer do not have horns they have antlers. There’s a big difference. Horns are permanent; both males and females have them. Many of our domestic animals like goats, sheep and cattle have horns.

Antlers on the other hand are borne only by the males. Antlers are deciduous – they grow and fall off every year. They are made totally of bone whereas horns are a core of bone surrounded by keratin, the same material that your fingernails are made of. Many of our North American mammals have antlers – moose, elk, caribou, and, of course, our local black-tailed deer.

By early spring the days are getting longer. This increased daylight passes through the optic nerve of the deer and stimulates the hypothalamus (a small but important part of the brain). This organ, in turn, causes the pituitary gland to dump the male hormone, testosterone in the blood stream. This chemical causes many changes in male deer –thickening of the neck, growth of antlers, aggressive tendencies and an increase in sperm production. You guessed it, they get horny.

Antler growth begins with a soft moss-like skin called velvet that nourishes the growing bone – it provides the necessary nutrients and oxygen. By mid-summer the antlers are fully developed and the velvet is useless; the deer rub it off on small branches. You can easily find these rubbing trees along streambeds; look for loose strips of bark and even bloody velvet on young willow trees.

Antlers are what we call secondary sexual characteristics. They have no function in the day to day survival of the animals. They certainly don’t help the deer find food and shelter. But they do send a very clear message- “not only am I a healthy vigorous buck capable of supporting myself but I have secured enough extra nutrients to grow an especially large set of antlers. I am one tough dude!” This message isn’t directed at female deer like you might suspect but to males. In order to mate successfully a male deer must dominate other male deer. Usually all that’s necessary for dominance is a raised head, erect hairs, and a rut-snort or two. Occasionally battles do happen but these clashes rarely result in injury.
Soon the dominant bucks will begin to corral several females into small groups. In the past biologists have described this breeding arrangement as a “harem.” Biologists, like most other people, bring their biases to work with them. Harem connotes control but these does are choosing to be with this buck, allowing him to corral them. It is to her benefit to mate with a dominant and fit male. Her offspring will inherit half their genes from that buck. Female choice is now the watchword in many breeding systems that were once described as harems.

The bucks must wait for the does to come into estrous. They continually taste the females’ urine. By curling their upper lip the urine is exposed to a special receptor on the top of the palate called the Jacobson’s organ. This organ tells the buck whether the female is in heat. Actual mating is a fairly stereotyped ritual.

After the breeding season is over, the males split. The testosterone level drops. By January most bucks have shed their antlers and mellowed out.

The females carry their developing young for about 6 1/2 to 7 months. Usually twins are born in March or April and weigh about 16 lbs. Fawns apparently have no odor. When threatened they curl up and remain perfectly still on the forest floor. Predators walk right by the camouflaged and odorless fawns. In three months they are weaned, losing their spots and foraging on their own.

The following spring the young males begin growing their first set of antlers. These small antlers are called spikes. The cycle begins anew.

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Skills

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August 6, 2009