Scientists and Hunters Ponder the Whitetail Rut

I used to think that I had seen pretty much everything there is in the woods and on the waters of eastern North Carolina. But, I witnessed something recently that I’d never seen before. I watched a buck deer make a scrape, literally right in front of me.

While seated on a ladder stand adjacent to path that runs between a grown-up cutover and a stand of hardwoods, I heard movement. It was a deer, a cow horn, and he was directly beneath me. As I watched, he moseyed onto the path, nibbled at a few acorns and stretched his neck toward an overhanging limb. Then, he stepped back, pawed the leaves from a spot on the ground with his front feet, squatted over the small, cleared patch and urinated on it. He did this within 10 feet of where I was sitting. He didn’t pick up my scent, probably because I was about 15 feet above ground level. That’s one explanation for his nonchalance. Another one is that, like nearly all male deer this time of year, he was starting to be distracted by his surging hormones.

Bucks make scrapes to mark their territory and to announce their presence to receptive does. Hunters understand that setting up near those spots doesn’t guarantee success but it does put them in areas that are frequented by sexually mature bucks. Whether those deer have the other characteristics – body size and antler development – that would classify them as suitable for harvest, is up to the hunters’ judgment. Hunters also know that the existence of fresh scrapes, those that have been tended recently, indicates that bucks will enter their “rut” period within a few weeks.

The question of what triggers whitetail deer to go into their annual breeding cycle has bedeviled hunters ever since they first took to the frontier woods wearing buckskin and toting flintlocks. Homespun logic said it was triggered by natural, meteorological phenomena such as the first frost of the year, the first full moon after the fall equinox, or even the first nor’easter storm of the year.

But then, starting about four decades ago, researchers in various parts of the country began applying scientific methods to the topic. Their goal was to unravel the mystery of the rut, to be able to predict it with some degree of accuracy. Those scientists found that certain givens apply to all whitetails, no matter where they are found. One is that whitetail does become sexually mature at about 1 ½ years of age and, when bred, usually produce single or twin fawns. Another is that the estrus (heat cycle) of female deer lasts about 5 to 7 days, with a 24 to 48-hour period in the middle being the “prime time.” A third fact is that buck deer begin seeking mates a week or so before the does’ estrus and continue to follow what they hope are receptive females as much as a week after it ends.

However, researchers like Wayne LaRoche, a Vermont biologist, have systematically studied deer behavior and physiology and have found that the whole process is more complicated than that. For example, LaRoche found that five general factors affect variations in the dates that deer breeding takes place from one year to the next. Those factors include:

age structure of the local population – Young does breed later than older, mature females.

sex ratio – The more does in the herd, the longer the rut period.

health of the herd – Deer in prime range and in excellent health breed earlier and with more intensity than animals in marginal areas.

genetics – It was found in one experiment that deer transported to Georgia from Wisconsin bred two months earlier than those in Alabama.

latitude – Proximity to the equator seems to play a role. In northern states, the breeding period for deer is more compacted and intense. To the south, it’s more protracted and less feverish.

LaRoche maintains that the movement of the earth around the sun is the major engine that drives the breeding cycle in deer. Deer that had rutted in November in the U.S. shifted to an April period when taken to New Zealand. The conclusion was that annual changes in solar radiation and lunar illumination, not the calendar, dictate when the rut takes place. LaRoche developed a computer program that demonstrated how deer rutting behavior changes in relation to diminishing light levels from day to day and week to week.

Animal physiologists say that LaRoche’s theory can be explained by the existence of a “pineal gland” in a deer’s brain (in fact, in all animals with a cranium, including humans). The sole function of this gland is the secretion of the hormone melatonin and how much of this substance is secreted is controlled by light intensity. Low light levels stimulate the production of melatonin and high light levels inhibit it. Researchers maintain that the light data is received through nerve pathways originating in the eye. When light levels are low over prolonged periods of time, high levels of melatonin trigger the release of sex hormones from the pituitary gland, bringing the animal to sexual readiness. “Photoperiodicity” is the term used to describe the amount of light reaching the eye.

So, since the scientists know all of that, why can’t they predict exactly when the rut will begin in any given area each year? That may be because there are several factors that influence photoperiodicity. One, of course, is the revolution of the earth around the sun while it tilts 23 ½ degrees on its axis. Others may be “precession,” the wobbling of the earth as it rotates, and reflected from the moon. And, how about localized factors such as drought, unusually high temperatures, storms and human disturbance? Any or all of these may influence deer in a small given area.

One thing that research has shown is that does who don’t conceive during their first estrus of the season usually enter another reproductive cycle, sometimes called the “second rut,” 21 to 32 days later. According to the N.C. Wildlife Commission’s calendar, the initial rut in the coastal plain is supposed to occur this year during the first week in November. The secondary rut should take place during the first and second weeks in December. Such facts don’t guarantee that a hunter will be successful then but it does give an individual something to think about while he is sitting in a tree stand, waiting for a ten-pointer – or maybe that cow horn – to happen by.