Hunters follow some pretty crazy theories when it comes to that mythical period known as the rut: A little cold weather and the rut will get going. It won’t happen until the full moon. The truth? Neither hold any water.
Numerous studies have examined whitetail breeding behavior and the various factors that influence it, or in some cases, factors that don’t influence it. One comprehensive study conducted by three leading deer behavior researchers at the University of Georgia found that lunar phases have nothing to do with the timing of the rut.
Karl Miller, David Osborn and Robert Warren used various data sets from state wildlife agencies that determined breeding dates. Their goal was to determine if indeed the various moon phases had any effect on whitetail doe estrous cycles, and thus, the rutting activities of bucks. Breeding date data were gathered through various means, including fetuses collected from road and hunter-killed deer. Also, researchers in Michigan sedated and captured pregnant does from within a one square mile fenced enclosure and X-rayed the deer and then measured the fetus length. According to Warren, biologists can determine the age of an unborn deer to within seven to 10 days by measuring the length of the body between the forehead and the rump. From that, they can count backwards to determine when the doe was bred.
Breeding dates were gathered from over 100 captive deer in four states and more than 2,500 free-ranging does in seven states. The information was gathered over a period of three to 19 years, depending on the state, and then compared to lunar cycles throughout the birth date ranges.
“We would expect annual breeding dates for a population to be similar if calendar date (thus, the same length of daylight) was the driving influence,” explains Osborn. “We would expect annual breeding to be less similar if moon phase is the driving influence because a particular moon phase might vary as much as 28 days across years.”
Scientists have long concurred that photoperiod—the length of daylight—has more influence on whitetail breeding activity than any other factor, despite what some hunters insist. Osborn says the evidence is quite clear. The phase of the moon has virtually nothing to do with the timing of whitetail breeding activity.
Warren adds that breeding activity in northern latitudes typically takes place over a short period of time but tends to be far more intense. Southern deer, on the other hand, enjoy a more leisurely breeding season, sometimes lasting months.
“Evolution has worked to time the birth of fawns so that survival rates are maximized,” said Warren. “If they are born too early in the year the does may not be able to provide vital nutrition in their milk because the forage won’t be available. If they are born late, the fawns may not have had enough time to become healthy enough to survive the winter. That 28-day variation that would coincide with the moon phase theory would mean that fawns could be born 28 days before or after the peak fawn birth date that takes place pretty much the same time every year.”
Weather can influence breeding activity, but not to the extent that many hunters believe. It doesn’t take a cold snap to trigger the rut. Again, nothing matters more, says Osborn, than the amount of daylight.
“Weather can affect rutting activity, but it doesn’t affect the timing of the rut itself. Deer don’t like to move in hot weather any more than you or I do,” notes Osborn. “They will continue to breed, but more often at night.”
Deer hunters who believe that moon phases and weather affect the timing of the rut may have the upper hand for the simple fact that it helps them hunt with a higher level of confidence and a higher degree of intensity. It doesn’t take a scientist to know that those who stay in the woods longer and stay focused are the ones who tend to have the best success.