Instincts, communicated through hormonal urges, insist upon deer that they reproduce.

That's the prime wildlife directive: Make more of your kind so the species survives. And when that natural obligation is carried out among deer, the process is called the rut.

All species, including our own, have trials and tribulations surrounding reproduction. Deer, however, are one life form that breeds only once per year. Geographically it varies somewhat, but at our latitude, the bulk of the breeding is concentrated into a very few days.

Individually, females are ripe for breeding and receptive to it for only about 24 hours. As Jerry Reed sang, when you're hot, you're hot. When it needs to happen, it needs to happen right then. That's why the rut gets, well, crazy.

There's an urgency to it. The physiology of each doe determines when mating can take place. To make it happen, a buck must be there and participate, so to speak, at the right time.

The kicker is that most adult does come into heat, come into estrus, within a short period of time. A very few days, possibly four or five, covers the breeding window of a majority of does.

There is a bail-out for those that somehow miss the boat. A doe that comes into estrus and doesn't get impregnated will come back into estrus again 28 days later, say biologists. That's usually not necessary because the bucks in normal populations usually are up to the job the first time.

Biologists say most prime breeder bucks will mate with multiple does. That's necessary because mature bucks that claim most of the breeding rights typically are well outnumbered by the does. Buck-to-doe ratios of 1-to-10, 1-to-15 or more extreme spreads aren't rare.

At the least, that means that bucks get really busy when the action fires up. An enthusiastic impregnator may spend 20 to 24 hours with one doe, then strike right out to find the next ripened candidate. In those cases where a dominant, mature buck can't show up at the right time, there's usually a buck as young as a yearling (1 1/2 years old) that will take advantage of the absence of superiors to try out this breeding thing for the first time.

Science tells us that the breeding phase from the buck perspective is a much longer haul. A buck is theoretically capable of breeding from the time its annual antler growth hardens in late August or early September until those antlers are shed in the winter -- as early as December but maybe as late as February or even March. The hormonal surge/decline that affects breeding potential also governs those antlers.

Buck hormones run higher approaching the time that females near estrus. Nature has the sense to make the boys' and girls' interest in breeding peak concurrently.

The signal for both bucks and does, that which triggers those lusty hormonal levels into overdrive, is the daily length of daylight -- what biologists call the photo period. It's effectively the same every year. When this time of fall comes, the sun-brightened period growing ever shorter day by day, at a certain point the endocrinal systems of the deer turn on their inner red lights.

They don't have to think or plan about the rut. The photo period simply pushes their buttons and they instinctively react when it's time.

Regularly, the peak of the rut -- at least the activity that we humans observe -- comes about a third to halfway into November. Conditions like unusually warm temperatures may slow the onset of the rut activity somewhat, but more likely, rut behavior is pushed into the hours of darkness when we don't see it.

During those years when less than ideal conditions seem to us to depress the rut, doe deer still get pregnant and bear fawns the next spring. So, did warm weather stop the rut? No way. The photo period brought it in as usual. We humans just didn't notice it.

What the rut is from the human perspective is increased deer movement shortly before the actual mating time. Bucks ramp up their travels, especially during daylight hours. Bucks that are almost nocturnal under normal conditions will abandon some cautions to roam by day seeking does for procreation.

Does flee suitors when they aren't yet receptive, adding more movement. Also, during the period when the rut is building, does generally seem to stir more for purposes I fail to grasp.

As the breeding time approaches, bucks do their version of social media, making (peeing in) and visiting scrapes on the ground, brushing against and scenting overhead branches, and antler rubbing and scenting small trees and bushes. Even before they actively chase after does, they move about advertising their presence with these behaviors.

To most people, as motorists, this extra movement mostly means increased chances to hit deer crossing highways. To deer hunters, the upswing of the rut means extra opportunities to encounter deer, the whitetails roaming more and more often traveling in front of waiting hunters positioned in tree stands and ground blinds.

Kentucky's firearms gun season for deer hunting begins today, the second Saturday of November each year, because of this.

Predictably, the chaos of the rut will pay off late next May and early June with tens of thousands of baby whitetails deposited in Kentucky habitats. The species re-seeds itself as nature intended.

Steve Vantreese, a freelance outdoors writer, can be contacted at

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