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You Need To Know The Science Of The Whitetail Rut

Understanding what goes on in a whitetail buck's body and brain during the most anticipated time of hunting season can help you tag your next trophy.

You Need To Know The Science Of The Whitetail Rut

Hunters everywhere anticipate the month of November, but do you know why? Ultimately, it boils down to two things: shortening days and increasing testosterone. Photo by Ryan Yoder 

All seasoned whitetail hunters live for November. Whether you are a weekend warrior or a vacation-day hoarder, we all like to get as much time afield during the best month of the calendar year. On Nov. 3, 2019, I was making a hyper-aggressive play on a large non-typical buck that I had been profiling for about 14 months.

I had just started my three-week rutcation, and the vacation vibe had me amped as it usually does. After a busted deep-timber hunt the afternoon before, I left the field kicking rocks and scratching my head, feeling snake bit already with nearly a month left to get it done. Before going back to the house with my tail tucked between my legs, I drove to an adjacent property after sunset and pulled three trail camera cards from the timber’s edge near a standing cornfield. The images garnered from this spur-of-the-moment, in-the-dark card pull were about to change the course of my entire season.

I had been profiling the large non-typical buck for about 14 months at that point, and the animal was seen on each of those three camera cards, with multiple passes from different directions and in broad daylight. In several of the images, the buck we call “Son of Sam” looked like a punch-drunk robot set to autopilot. With an open mouth breathing and eyes glazed over, he was stomping the Illinois landscape and searching a doe bedding thicket nearby. The big rascal was certainly under the influence of his surging testosterone levels, and as a hunter and a veterinarian with a strong endocrinology background, I knew right then and there I needed to make my move. Testosterone was making the Son of Sam buck vulnerable!

The author’s decoy setup is shown here; he positioned his tree stand on the wood line the decoy faces in the middle of the night after receiving photos of his target buck. The author’s knowledge of the rut timing in his area, based on shortening day length, helped him predict when his target would be most vulnerable to an aggressive strategy. Photo courtesy of Clint McCoy, DVM


Have you ever wondered why hunting seasons across the nation occur when they do? The answer is simple. Whitetail deer are known as short-day breeders, meaning day length plays a role in the hormonal balances that drive the rut. This causes an increase in observed movement and allows hunters afield during the peak of breeding season to harvest more deer. This leads to more deer being harvested for population control, more hunter participation, and better new hunter recruitment and retention for the future of the sport.

The whitetail deer is a wild counterpart to domestic sheep and goats, because they are all ungulates, ruminants, and they are all short-day breeders. After the summer solstice occurs on June 21, each day’s length begins to shorten. In my area of Illinois, the summer solstice results in roughly 15 hours of daylight and only 9 hours of darkness. During the following months, July 21 produces 14.5 hours of daylight, Aug. 21 shows 13.5 hours, Sept. 21 comes in at 12.25 hours, Oct. 21 produces 11 hours, and finally, just under 10 hours of daylight occurs on Nov. 21.

A hunter that is casually reading may ask, “What does length of day have to do with filling my freezer and punching tags on trophy bucks?” If one understands what is happening inside the animal on a hormonal level, one can increase their odds of bagging a buck in November! As day length gets progressively shorter, big things begin to happen regarding whitetail anatomy that drive the rut. And learning this is key in taking advantage of the power of one hormone: testosterone.


What do 1980s professional wrestlers, 1990s-era MLB homerun hitters, teenage men and big, mature whitetail bucks have in common? They all thrive on the hormone testosterone!

In whitetail bucks, as daily photo-period reduces with shortening days, a tiny little organ in the cervid brain begins to wake from its endocrine slumber: the pineal gland. The pineal gland responds to light reduction by secreting another hormone called melatonin. Melatonin increases gradually throughout the shortening days, resulting in a hormonal cascade involving the brain’s hypothalamus and the pituitary gland. The end result here is the pituitary gland’s hyper-secretion of two more hormones, LH and FSH. And in the whitetail buck, these two compounds hit the blood stream and head straight to a buck’s testicles. This is where the magic happens!

FSH acts on the buck’s testicular Sertoli cells and causes them to start producing sperm cells for breeding. LH in the bloodstream tells testicular Leydig cells to make one thing and one thing only: testosterone. Now, after the process began around the summer solstice and built until the middle of November, the whitetail buck has become a fully functional breeding machine. And he has a body and demeanor to match!

Just what does testosterone do for the whitetail buck’s body and mind? Read on!

As days shorten, a whitetail buck’s pineal gland responds by releasing melatonin. Increased melatonin causes the hypersecretion of FSH and LH from the pituitary gland, and these two compounds enter a buck’s testicles, prompting an increase in testosterone and sperm cell production. Essentially, this process that all starts with shortening days, is the “science” of the whitetail rut. Photo by Ryan Yoder


We’ve all heard about those 1980s professional wrestlers and the PED scandals that rocked baseball during the homerun era. And those of you reading that have been teenage men, you know how testosterone can make you a bit “love drunk” or crazy brave. The hormone compound is no different in the whitetail buck’s body!

Testosterone is an anabolic steroid. This means when it is present in the blood stream in mass quantity, the animal begins putting on muscle at a rapid pace. It gives the animal strength, power and bone density in preparation for the rigors of the rut. Think survival of the fittest here. The stronger you are as a whitetail buck of breeding age, the more likely you are to service many does and hack the beatdown winter will put on when breeding stops.


Testosterone is also an androgenic steroid, meaning when present in the blood stream in mass quantity, the animal’s behavior changes. His libido (sex drive) shoots through the roof. He becomes fearless and is prone to taking risks, like being visible on foot during daylight hours. Bucks can even become compulsive in pursuit of does to breed.

Lastly, testosterone makes mature bucks aggressive toward fellow breeding bucks and influences their competitive spirit. Testosterone can make a big buck feel invincible, and given the right individual, the animal can and will fight to the death to assert his dominance over other bucks. Testosterone is the source of a fair number of black eyes and fist fights for 20-year-old adult males at college frat parties, and white- tail bucks are no different.

The point here is quite simple! Understanding when and where to “pick on” a mature buck’s testosterone flow can be freeing as a deer hunter, and I will outline this strategy soon.

After learning that increasing levels of testosterone caused the buck he called Son of Sam to become aggressive and break many of his tines, the author used a buck decoy to lure-in the non-typical the following season. Photos courtesy of Clint McCoy, DVM


Early October is a difficult time to chase mature bucks, but I’m going to discredit a commonly held myth in deer culture: there is no such thing as an October Lull. Period. The science out of the Mississippi State Deer Lab proves that. As day length proceeds to drop through the month of October, testosterone is rising daily in the animal. Therefore, one can see a linear and upward curve in daylight activity of mature bucks, even in October. My favorite time to hunt in October is between the 15th and 31st. And I’ve been successful in taking some tremendous bucks during this period.

After Halloween, a buck’s testosterone levels are bursting at the seams. This is the time of season when the hunter can take risks and crowd a buck tight to his bedding cover. Throw caution to the wind, the bucks certainly are! I try to spend as may hours in a tree stand from Halloween until Thanksgiving as possible, because I know if I am to take a mature buck, I must harness every hour of legal shooting light I have to get the job done. Pair this mindset with the animal’s risky, libido-driven competitive spirit, and you have a recipe for success year in and year out!

Son of Sam eyes the author’s decoy moments before the author arrowed him. Photo courtesy of Clint McCoy, DVM


One final strategy I deploy when mature buck hormones are surging, is the use of calls and decoys. This tactic is how I tagged the Son of Sam buck I mentioned earlier in this article. I had known this individual buck to be a fighter from the year before. By the end of the year prior, every tine he had was snapped in half and his coat sported thick scars. The Browning trail camera images told me the story clearly; this bloke likes to fight.

During the night of Nov. 2, 2019, after receiving the daylight images of Sam, I immediately ran back to that farm with a mobile tree stand and a fighting buck decoy. I placed the decoy 15 yards from the tree, and I soaked that fake in about a gallon of tarsal spray scent.

The sunrise came up on a frosty, gorgeous morning, and there was a light and variable wind. I was standing up admiring a large fox squirrel when I looked down to see the Son of Sam. The buck stepped out of some standing corn and was mesmerized at the sight of the fighting buck decoy. I let out a soft grunt and snort-wheeze, and the large non-typical approached, lip licking and hair bristling. The animal was met with a well-placed arrow!

To this day, this hunt is the most polarizing of my solo, DIY career. And I did it by harnessing the power of testosterone toxicity!

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