Have you ever wondered exactly when the peak of the breeding season occurs on your very own hunting grounds? Are the hunting magazine articles too general and not specific enough for you? Have you read the TPWD brochure showing the eco-region peak breeding dates? All of these offer great information but some folks desire much more specifics for their own ranches. Continue reading for more information and details to help you determine the peak of the breeding season on your very own ranch.
Back in the late 1970’s and early 80’s, deer researchers began developing a method to understand the exact dates of breeding activity. This technique involves aging a fetus based on its size and then backdating to determine conception dates. The technique has proven extremely accurate and valuable to land managers and hunters in order to better understand their specific herd dynamics and when to make specific management decisions.
The method involves removing the fetus from a harvested doe carcass and using a fetus scale specifically created for such tasks. The scale not only measures the length of the fetus, but also uses the Julian calendar to backdate in order to determine the specific conception date. It also provides the ability to foredate to estimate the date it would have been born. This information is important for managers to detect changes in breeding dates with respect to adult sex ratio and herd management programs.
Here is a typical crown-to-rump measurement example:
For this exercise, let’s say the doe was harvested on December 28. The fetus in this photo is 64 days old. The Julian date for December 28 is 362. This number minus the fetal age in days (64) is 298. The Julian date of 298 occurs on October 25 and this is the date of conception.
The number of days to parturition (birth) was 134, see scale. This number, added to the Julian date of the harvest (362) is 496. The Julian date of 496 occurs on May 11 and that is the projected date of birth. So the doe was bred on October 25 and would have fawned on May 11, great information you would have never known without this exercise.
I harvested this northern San Saba County doe two years ago on December 28 so this tells me that the rut was on the last week of October and that the first wave of newborn fawns hit the ground on or about May 11 that year. This information is valuable and helps me to decide if I want to have cattle in that particular pasture at that time, decide when to harvest a crop or perhaps use heavy equipment in my pastures at that time. Perhaps I will defer grazing in that pasture for a few extra weeks to allow maximum fawning cover to remain or maybe I can use the local trappers or helicopter to help me lower the predator population in the weeks leading up to the peak birthing dates. This information also tells me I need to be enrolled in the MLDP program so that I can harvest bucks with undesirable antler traits before they breed instead of waiting on traditional November rifle dates to remove those bucks. This data also tells me approximately when the secondary rut will be (28 days after the primary rut) so that I may expect more mature buck activity.
So you can see how useful and practical this information can be. Some folks cringe at the facts and others like to claim never to shoot does late in the season because they may be pregnant. This technique and exercise proves that if you shoot a doe in San Saba County in the month of November, you are indeed harvesting pregnant does.
Take this information to your hunting camp and see what you learn. I suspect you can win a few bets and impress your buddies around the campfire with it.
What, exactly, is the rut in whitetail deer and why do hunters enjoy it so much? What causes the normally secretive and elusive mature bucks to temporarily lose their minds and wander out into a wide open field during the hunting season? In this two part series, we will take a deeper look into the science and biology of this incredible, annual, phenomenon hunters call “the rut”.
The drive of self-perpetuation is a strong one. It is more than just “survival of the fittest” and includes a myriad of hormone and chemical responses throughout the body triggered by nutritional and environmental factors alike. Assuming the animals are healthy, let’s look closer at exactly how the rutting behavior happens.
Courtship: Running is a large part of the whitetail’s courtship behavior. Bucks travel great distances in search of females that are nearing receptiveness, or estrous. They use their nose exclusively to determine if a doe is getting close as they travel from doe group to doe group in search of a potential mate. During this time, bucks may lose up to 30% of their body weight as they feed and rest rarely during such extensive travels. The females that are nearing estrous, but just not quite ready yet, will run from the buck’s asserted charges. At first a trot, her fawns will usually follow as they can. As her receptiveness increases, the chase tends to resemble a track meet and the fawns are usually then left far behind. As the receptiveness of the doe peaks, the chase slows down and the two spend more time closer together, even bedding down together at times. Once the doe is completely receptive, she will stand for the buck and allow him to rest his head on her rump. Soon thereafter, copulation takes place but lasts only a few seconds. After mating, the pair split up and the buck begins the same cycle over and over again. In a nutshell, the peak of the rut is simply the period when most of the females are in estrus and the healthy mature females dictate the timing of the rut.
Timing: The timing of the rut depends on your general location, or latitude, where you hunt. Except near the equator, the rutting season is tied to the photoperiod, or day length. The diminishing ratio of daylight to darkness triggers the start of the reproductive cycle each year in both sexes. Because photoperiod is tied to latitude, the rut progresses in North America from the north being the earliest and the south being the latest. In a nutshell, photoperiod triggers physiological changes that lead up to the rutting activities.
Nutrition: Because the actual rut peak is dictated by adult females coming into estrous, the nutrition and body condition of the females in the months proceeding up to the rut plays a key role in the exact localized timing. Weather and temperature also are factors, but once the photoperiod has prepared the females physiologically for breeding, cooler weather and a drop in the barometer certainly helps in getting the deer on their feet more often. Unseasonably warm weather suppresses rutting activity. Obviously, a body that is lacking from adequate nutrition cannot and will not function properly. In this scenario, females fail to enter heat, or estrous, and therefore can’t get pregnant or cannot maintain their pregnancy which ends in the same result. The males can’t maintain the physical strength or their hardened antlers long enough to participate and thereby cannot contribute to the gene pool.
Biology: In both sexes, a pea-sized gland near the center of the brain is called the pineal gland and it receives input from the eyes that triggers the release of a hormone called melatonin. As the days become shorter in the fall, more melatonin is secreted and this increased melatonin acts on the pituitary glands and regulates the release of a host of different hormones. Such annual cycling is responsible for the different hair coat changes, food intake levels, antler growth cycles, ovulation and timing of the overall rutting activities. If the pineal gland is damaged or interrupted in any way, the timing of these natural seasonal cycles is compromised.
In females, follicles in the ovary produce estrogen—the hormone responsible for the doe’s mating urge. Another ovarian hormone, progesterone, acts with estrogen to promote optimum heat—or the time when a doe will permit actual copulation. The rise in estrogen eventually causes the release of a mature ovum for the buck’s sperm to fertilize.
In males, the testicles are separated into three production phases: primary development, full production and resting. The phases are directly related to the onset of antler growth, the shedding of velvet, and the antler casting period. The growth and sex hormone, testosterone, is produced to begin live sperm production. Viable sperm production, measured in the billions per ejaculation, increases slowly up until the actual peak of the rut and then begins declining as the mating season ends. Sperm production and testes size are greatest in males aged three to seven years of age, however, buck fawns, given the chance, can successfully impregnate females. Testosterone dictates the course of antler development, so any damage to the testicles during any stage of the antler growth process will usually result in the antlers being held in limbo and may cause severe deformities or a permanent velvet stage to remain, regardless of the season.
So, now you know how and why the rut begins and what triggers and controls it. Next time, we will discuss the management implications and how you can use this information to grow a quality deer herd on your own property.
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Every deer hunter worth his salt knows that hunting during the rut is likely the best time to harvest a mature buck. Last issue, we explored the mechanics and biology behind the rut and why and how it makes mature bucks do the silly things they do and therefore makes them vulnerable to your weapon of choice. This issue, let’s discuss HOW deer managers can use the rut to their benefit to help them manage their deer herd.
You are likely familiar with the primary stages of the rut: pre-rut, rut and post-rut. Some will argue that there are additional steps or levels and there certainly is if you use a microscope, but for generalized management purposes, the three main categories are close enough. Obviously, the pre-rut period is where the bucks begin to think about it but the girls are not. Coming out of the summer bachelor groups, the bucks begin to rub the velvet from their antlers and begin settling the pecking order among their previous best friends. The bucks are building fat reserves, working their necks out and in general getting ready for the impending challenges that they know lie ahead of them. From a deer management perspective, THIS IS THE TIME TO INCREASE YOUR HARVEST of breeding-aged bucks that you DO NOT want in the herd. The bucks are still very predictable and relaxed. Now, a deer hunter oftentimes wants to harvest the biggest deer in the pasture while a deer manager wants to harvest the sorriest deer in the woods. Don’t get excited here, but there are real differences from recreational hunting and serious management. For deer managers, the pre-rut is the best time to remove those bucks with undesirable antler traits BEFORE the rut and they have the opportunity to spread those undesirable genetics into the herd. As a manager, this is the perfect time to be afield in order to remove such animals well before the breeding period. By this time, deer surveys should have been completed or at least winding down so you should have a good idea of antler quality, age structure and fawn survival rates. All of this data will be useful as you set your standards as to what is, and is not, a buck with undesirable antler traits. Every ranch is different and personal opinions are varied, but use the buck herd on YOUR ranch to help you decide where the cut-off should be.
With the bucks being less mobile and more predictable, now is the time to hit them hard to remove those that you have determined as undesirables. Letting the higher quality animals go while removing the lesser quality animals is how genetic gains are realized. Bucks wear their genetics on their head. Look at his genetics and ask yourself this one very simple question, “Do I want more of the same?” If the answer is yes, don’t shoot. If the answer is no, shoot him now and don’t wait. The pre-rut period may last for several weeks or perhaps a month. There is plenty of time for the serious manager to get the job done even if the weather, wasps, and mosquitoes are against you.
The rut is when all bets are off and all stops are pulled. Bucks you have never seen before magically appear out of thin air. Mature bucks you weren’t sure were still alive certainly are and the woods come alive with buck activity. At this time, most folks shift to trophy buck hunting and that is fine. But, the chance to still take a buck with undesirable antler traits still exists so be ready to take him anytime you can. Passing on two or three undesirable bucks in hopes of taking a trophy may not be the smartest thing to do when extensively managing a deer herd, but human nature certainly makes it easy to do so. If you harvest the trophy buck too early, he may not have had the opportunity to breed, so keep that in the back of your mind. Are you hunting for your ego or are you hunting for management purposes? You be the judge here, just realize the results of your decisions may last for years to come.
The actual rutting period is not that long. It may last one to two weeks and that depends on the health of the animals, the adult sex ratio, the weather, and the habitat, so hunt hard as it will end quickly. Of course, 28 days later another cycle will hit but this will depend on the adult sex ratio, weather and habitat too, and it won’t last nearly as long. Hunting the rut is certainly a rewarding time of the year so get the management bucks out of the way so that you can relax and enjoy the magic and perhaps take the buck of a lifetime after he breeds.
The post-rut is the rut in decline. The female receptiveness and availability is reduced but the buck’s desires are not. As fewer and fewer females are receptive, the buck’s travels must increase as his evolutionary desire to reproduce is still strong. The body weights are now 20-30% of what they were two and three months ago and food consumption is not a priority. Bucks travel great distances and simply lean forward in their lust to find a receptive female. At this time of the season, a manager must be very aware of broken tines before pulling the trigger. Good optics are a must when harvesting bucks now as the body condition won’t help determine age due to the deleted muscle and fat reserves and missing tines can camouflage a quality buck. Extreme care must be taken when selecting a buck for harvest now, but it can still be effective. Certainly, breeding has already taken place earlier by those remaining undesirable bucks, but you can still harvest him now before any additional damage is done and he doesn’t need to get another year older.
So, using your knowledge of how, why, and when the rut begins, and all three primary stages, can help you better manage your deer herd. The first two stages of the rut are the best time to remove a buck you don’t want breeding while searching for a trophy buck allows you to concentrate on the final two stages. Take this knowledge to the woods and keep notes of the dates and stages of the rut as they happen in your woods. This will help you be a better hunter and manager from now on.by