As the lazy, hazy days of summer give way to clear, crisp days of early autumn, white-tailed deer begin preparing for the upcoming breeding season. Bucks are busy sparring with each other, rubbing trees, and creating scrapes. Their stamina and dominance will be tested in the upcoming weeks but the reward is immortality in the form of spotted fawns next spring.
Ideally, the breeding season should be short and properly timed. This gives fawns the greatest advantage of survival with abundant food for lactating does and plenty of time for fawns to fatten up before winter arrives.
By far, the most popular question in the fall is "When is the rut in Pennsylvania?" To answer that question, the Game Commission collected breeding date information from road-killed doe in the spring of 2000-2007. Fetus length from these unlucky does was measured. From these data, we can determine the age of the fetus. Since the gestation period of deer is about 200 days, knowing the age of the fetus allows us to estimate when conception took place.
Over 6,000 doe were examined over this period. What did those unlucky doe tell us? Nine out of 10 does were bred from mid-October to mid-December. And the peak of the rut occurred in mid-November.
Sexual maturity in doe fawns is linked to body size which is related to the quality and quantity of the food as well as a birth date. Doe fawns reaching the critical size (80-90 lbs) come into estrous their first fall, but breed later than an adult does. Peak breeding by fawns occurred in late November and early December. Nearly half of all fawn breeding occurred from December to February. This probably explains the breeding activity observed by hunters after Thanksgiving.
Ninety-one percent of adult does and 26% of doe fawns were pregnant. The number of fawns conceived also varied by the age of a doe. Doe fawns generally had single fawns while an adult doe usually had twins. And triplets were rare.
But what about the moon? Hunting magazines and websites contain countless charts correlating the moon phase with deer movement and breeding. Often these articles will mention the "rutting moon," which is popularly defined as the second full moon after the autumn equinox. It is believed the "rutting moon" affects the timing of the breeding season for white-tailed deer.
Since we already know the conception date, we can compare that date to the date of the "rutting moon." Data show that the rut occurs in mid-November. But the "rutting moon" varies from late October to late November. So the only time the "rutting moon" corresponded to the median conception date was when it fell in mid-November.
So if you're asking when the rut is in Pennsylvania, the answer is mid-November. For deer, it's serious business and they aren't about to change their schedule for the moon or the latest marketing ploy.