AN EDUCATIONAL SPOTLIGHT ON "THE RUT"

What is the rut? When does it happen? Why does it happen? How long does it last? These are common questions among hunters. As a second-generation reproductive physiologist with over 17 years of experience in the whitetail deer breeding industry, I’m here to shed light on these mysteries. 

First things first: it takes two to tango. The “rut” happens when the required physiological (body chemistry) changes take place within bucks and does. Once these physiological changes begin to occur the rut, or the behavioral characteristics of whitetail deer during their breeding season, begins. 

What causes the required physiological changes that mark the beginning and end of the rut? Daylight duration is a major factor for the onset of the rut. Deer are “short-day breeders,” meaning shorter daylight triggers these changes. The pineal gland in a deer’s brain tracks daylight, and as fall progresses, it increases melatonin production. This stimulates hormones like LH (luteinizing hormone) and FSH (follicle-stimulating hormone). These hormonal pulses grow stronger as daylight decreases. For females, a peak in LH triggers estradiol production, bringing them into heat. For males, the hormonal spikes produce testosterone and viable sperm, making them highly aggressive. 

When does the rut start? It begins when the first does come into heat and bucks have enough testosterone to breed. Not all deer respond to daylight changes simultaneously. Here in Texas, it’s common to see rut activity as early as late October. However, most does come into estrus during the first two weeks of November, which marks the peak rut period across much of North America—though it’s later in Deep South Texas. 

The rut follows a bell curve: about 10% of does cycle early (before November 1), 80% during the first two weeks of November, and 10% later. This means the first estrus round spans about four weeks. What happens to does that don’t breed in the first round? Roughly 75-80% conceive, but 20-25% will return to estrus in 21 days. Early-season does that don’t breed will cycle again just as late-season does begin their first cycle, creating a continuous overlap of does in heat. For example, does that came into heat in early November and didn’t conceive will return in late November to early December, while late does have their first cycle in mid to late November. The result is a chaotic but predictable pattern with major peaks. 

What winds the rut down? As more does conceive, rut activity naturally decreases. By late December or early January, only a small percentage of does are still cycling. However, daylight duration remains within the reproductive range, so some rut activity can persist into February and even March. I’ve seen fawns born as late as September and October—evidence of this extended breeding season, given the 185-195 day gestation period.