Moonlighting for bucks
Few aspects of deer hunting generate more interesting conversation or create more controversy than the rut, the breeding season for whitetail deer and the glory days of each hunting season.
If I had a dollar for every time I have heard someone try to explain the rut, I would be a rich man. There are several different theories as to what the causes are, some of which receive more attention than others. The cause that is given the most attention is the lunar theory.
The lunar theory has come about in recent years after researchers — namely, Charles J. Alsheimer — conducted studies which supposedly show that the moon is the deciding factor in the timing of the rut. By their theory, the second full moon after the fall equinoix, which falls on September 21, causes the doe to go into her estrus cycle. This moon is also known as the "rutting moon," or the "hunter's moon."
Alsheimer is an outstanding writer and one of the most intelligent deer hunters in the world. But with all due respect to him, I think the moon's affect on the rut has been greatly blown out of proportion.
For starters, if the moon is the biggest determining factor on the rut, it would have to occur at the same time everywhere. Instead, the rut in the north peaks in early November, while the rut in the south peaks much later.
To his credit, Alsheimer does not claim that the moon affects northern deer and southern deer alike, as do many of his fellow researchers, but instead says that the hunter's moon only affects deer in the north. But if this were true, what kicks off the rut in the south? Why would the hunter's moon affect deer in some parts of the country but not others? Furthermore, Alsheimer and his partner, Wayne Laroche, conducted studies that found that about 70 percent of the does they studied went into estrus with the full moon. Why would the full moon send some deer into estrus but not all deer?
Whatever the factor that sends deer into their estrus cycle, it must be biological. Can deer in one area be affected by one factor while deer in another area are affected by another? In my opinion, no. All deer must be sent into their estrus cycle by the same biological factor.
Bryan Kinkel, a wildlife biologist from Nashville, says the full moon may affect the time of day that breeding occurs, but it does not affect the calendar date. Leonard Rue III, a field editor with Deer & Deer Hunting magazine, agrees. He says the timing of the rut is determined by photoperiodism.
Photoperiodism refers to the amount of daylight within a 24-hour period. In essence, shorter days are what sends a doe into her estrus cycle (though Kinkel is quick to point out that it is actually longer nights, not shorter days, that causes the doe to go into estrus). This theory was the generally accepted theory before the lunar research.
The problem is that, like the lunar theory, the days are the same length in the south as in the north. Therefore, this still does not explain why the rut occurs at different times in different places.
At this point, Kinkel puts a new twist on the situation. He says that photoperiodism is what triggers the rut, but the timing is strictly genetic. He says that all deer have their estrus cycle genetically encoded based on the best chance for fawn survival.
"In Texas, early spring can be a serious stress period for deer (due to dry conditions)," Kinkel says. "The summer rains start in the early hurricane season (July and August). Thus, the rut in south Texas is timed to produce fawns during the hurricane green-up in late summer.
"In contrast, the limiting factor on fawn survival in Florida is too much water. The tropical summer rains would drown fawns. Hence, the rut in south Florida is timed to produce fawns during the dry season (February and March). The rut is actually in July and August in south Florida.
"In the far north, severe winters and late spring weather are the limiting factors. If a fawn is born in early spring, the late winter storms would kill it. If the fawn is born in late summer, it does not have enough time to put on body weight before winter arrives and dies of malnutrition."
This theory of natural selection explained by Kinkel is logical and well-accepted. So if this is why the rut occurs when it does, what makes the rut occur when it does? In other words, what triggers the system? Is it hte moon? Shortening days? Is it, as some biologists believe, nothing at all; that if you take a deer from Tennessee and transplant her in Maine, that she will breed according to her Tennessee clock? Or is it some other factor entirely?
I personally feel that photoperiodism is what kicks off the rut. For instance, if deer are biologically engineered to breed in late October so as to produce fawns in early March, their reproductive system will know when the day shortens to a certain length that it is time to breed. But if this was true, why does the rut occur later or earlier in certain years? The day of October 16 will be the same length this year as it was last year.
This is where I go out on a limb that more hunters are starting to venture out onto. I feel that cooling temperatures play a role in triggering the rut. As Rue pointed out in his photoperiodism theory, "many dark, stormy days in October can fool a deer's pituitary gland into believing that the day's are shorter." Likewise, the same can be said for cooling temperatures. If the month of October (or November in the deep south) is warmer than usual, the rut can be a few days later. If it is cooler than usual, the rut can occur early. In addition, have you ever noticed how buck sign (rubs and scrapes) start to pop up everywhere after the first cold snap of the season?
This year's harvest moon is just now in bloom. Tomorrow (October 6), the moon will be full. Four weeks from now (November 6), a little later than most years, the hunter's moon will be upon us. If the lunar theory is actually fact, this year's rut could turn out to be a little later than normal. If photoperiodism is the deciding factor, the rut should be unchanged . . . unless, of course, it's pushed ahead or shoved back by temperatures. So far, temperatures this fall have been close to average, with a couple of cooler-than-normal days, but also a couple of warmer-than-normal days.
Regardless of which theory you choose to believe, there is only one thing certain about the rut: It occurs every year, and it is thrilling to hunt. Perhaps that is why entire books have been written about the subject without proving a thing. Maybe someday we will know all there is to know about the whitetail deer's breeding habits. In the meantime, all we can do is speculate.
This article has appeared in the Independent Herald, Tennessee Valley Outdoors Magazine and Bass Pro Outdoors.
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