Basic Biology of the Whitetail Rut

Basic Biology of the Whitetail Rut

Adolescence can be a rough period of life, both mentally and physically. Thankfully, we humans only have to experience it once. Imagine if you had to go through puberty every year!

In effect, that’s what a whitetail buck does each fall as he goes through the rut.

Purpose

The goal of the rut, according to Dr. Karl Miller of the University of Georgia, is “to maximize reproductive output in the spring.” It’s all driven by photoperiod, the amount of daylight on a given day. Light enters the deer’s retina, sending a signal through the optic nerve to the hypothalamus and then the pineal gland to inhibit the production of melatonin. At night, these impulses stop, causing melatonin to be released into the body. The gradual increase in melatonin due to the longer nights of fall and winter stimulates the hypothalamus and pituitary glands to secrete estrogen and testosterone — the rut hormones.

Miller noted that photoperiod is a much more precise trigger of seasonal changes in the north, and as a result, the rut is much more synchronous there. Northern regions have a wider and more dramatic range of daylight lengths, declining by approximately three minutes a day in autumn. The north also experiences a wide range of annual temperature changes — sometimes 100 degrees or more between summer and winter.


With such extreme seasonal fluctuations, it’s critical that fawns are born into a favorable environment in terms of temperature, security cover and forage, and that fawns are given as much time as possible to grow before the onset of the next winter. This necessitates that does be bred at the optimal time.


Studies have shown that peak whitetail breeding dates in the north are amazingly consistent. I once surveyed deer biologists from all across the whitetail’s range in the United States and Canada, and they agreed that peak conception dates fall at roughly the same time each year regardless of moon phase, weather patterns or other variables.

The southern photoperiod change is less dramatic and the climate less severe, so fawns born outside of peak birth periods have a greater chance of survival there. However, synchrony still has its advantages. By giving birth at roughly the same time, does can “swamp” predators with an abundance of prey, improving each fawn’s odds of survival.

Let the Games Begin

If peak breeding occurs around the same time each year, we can presume all of the other stages leading up to that do as well. The aforementioned surge in testosterone results in circulation to the antlers being cut off. Velvet dies and peels, and bucks begin rubbing it off. They also begin skill sparring, much like young boys wrestling. Bachelor groups are still together, but that won’t last long. Aggression gradually escalates to demonstrative sparring as bucks begin sorting out dominance. Adolescence has begun. Subordinates aren’t run off yet, and they may even groom dominants as a display of submission.

Meanwhile, making rubs begins to take on more importance. Through secretions from their forehead glands, dominant bucks communicate their status. According to Miller, one buck can make 1,000 or more rubs over a 90-day period each fall. Being able to communicate this way cuts down on actual physical interaction, which becomes more important as bucks become less tolerant of one another and as bucks and does seek one another out, which technically means they’ve entered the rut.


The next phase of the rut is establishing scrapes, which serve several functions. Scrapes provide a litany of information about their maker and visitors, including identity, age, health, social status and breeding condition.

Scrapes also help synchronize breeding physiology. Chemicals in the buck’s urine and scent glands stimulate the doe’s reproductive system, causing, among other things, ovaries to develop. According to Miller, if you take mature males away, breeding becomes less synchronous, which is often the case in heavily hunted populations with a high proportion of younger bucks.

Application

Once you have a benchmark, you can fine-tune your hunting strategy to specific stages of rutting behavior. With a phone call to your local or state deer biologists, you can find out roughly when peak breeding occurs in the areas you hunt. Then, adjust accordingly.


Peak chasing will be during the week or two leading up to peak breeding; prior to that, bucks will be more involved in rubbing and scraping. Bear in mind throughout the season that this is all based on “peak” breeding dates. There will always be a certain portion of rutting and breeding behavior occurring out of sync with the majority.

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