Biology Of The Rut

By T R Michels
www.TRMichels.com

Biology Of The Rut

Pheromones

Deer pheromones, the scents given off by deer, are used as a means of communication. Pheromones serve to stimulate a behavioral response in another animal. White-tailed deer pheromones are present in the forehead, interdigital, tarsal and metatarsal glands while estrogen and testosterone are found in the urine. There may also be pheromones associated with the pre-orbital gland and saliva. Many of these scents are used in combination during self impregnation (rub-urination), and sign post marking (rubs, scrapes) and are interpreted by individual sexes and age classes differently. When used by themselves these scents may be interpreted differently than when they are used in combination with another scent or scents.

Recognition and Trailing Scents

Tarsal scent from the gland on the inside of the rear leg is used in combination with urine as the primary recognition scent in whitetails. This scent is both sex and age specific and deer encountering tarsal scent from another deer can determine the sex and relative age of the other animal by it's scent. Tarsal is used in combination with urine during rub-urination all year long when the animal urinates over its rear legs. All deer rub-urinate, often just after rising from their beds. Bucks rub-urinate more frequently during the rut while making scrapes. Rub-urination is used by moose and possibly elk in response to danger, probably as an alarm signal. Deer often sniff and lick each other's tarsal area during social grooming for identification, which helps to reinforce the social hierarchy. Because of this they know the smell of all the animals in their areas. I have noticed flared tarsal gland hair when bucks fight, and tarsal scent may serve as a danger or dominance signal in this instance.

The Metatarsal gland on the outside of the leg is largest in mule deer, next largest in blacktails and smallest in whitetails. It's been suggested that blacktails, and possibly mule deer, use Metatarsal scent when alarmed to express danger. It's not totally understood in whitetails.

Interdigital scent from the gland between the hooves of all four legs is used by deer to track each other. Does and fawns use it to locate each other, bucks use it to track does. The scent of each individual deer is so specific that one animal can track one individual no matter how many others are in the area, and because scent molecules evaporate at different rates an animal can also determine which direction the other is traveling.

Forehead scent from the sudoriferous glands between the antlers is used as a recognition and dominance scent. Prior to the rut bucks take part in social grooming, sniffing and licking the forehead and tarsal area. Later, when sparring and fighting begin, dominance is established and the bucks recognize each other by scent and associate it with social level.

Bucks are able to recognize the scent of other bucks once signpost marking begins, and know which rubs and what overhanging branches at scrapes have been visited by which buck. After being threatened or attacked during the pre-rut and rut, subdominant bucks soon realize they should not be in area's near a dominant buck and it's rubs and scrapes.

Recognition scents are present all year and can be used any time during the rut, or any time of the year without fear of alarming deer. However, forehead scent is most prevalent during the rut and is more effective at that time. Because deer are curious about their home range, and often exert dominance (even does) in their core area they may investigate any new scent to find out what deer had been in the area.

Territorial and Dominance Scents

Both the signposts of rubs and scrapes are "dominance areas" of mature bucks. These signposts mark the areas used by the buck. Each rub contains scents from the Forehead glands. After rubbing bucks often lick the rubbed tree, and because they sometimes lick their own tarsal after rub-urinating there may be urine, testosterone, tarsal and saliva left on the rub. This combination of scents is a territorial signal proclaiming dominance by mature bucks.

These same scents may occur on the overhanging branch at a scrape (urine, testosterone, tarsal and saliva, possibly pre-orbital) because the buck sniffs, licks, rubs and chews the branch with his forehead and antlers. Urine, testosterone and tarsal are deposited in the scrape during rub-urination. The buck also leaves interdigital scent on the trail of his rub line and in the scrape as he paws the ground. This combination of scents is again a dominance and territorial signal to other bucks and a sign of a mature, dominant, breeding buck to the does.

The complex combination of scents left on signposts occurs primarily during the rut. The scents at the rub occur when bucks begin to shed their velvet. The scents at scrapes begin shortly after rubbing begins, but become most evident about a month later. These scents can be used anytime during the rubbing phase to attract bucks, but they become less effective after the first breeding phase. Because a dominant buck makes rubs and scrapes as a prelude to breeding as a proclamation of dominance, he is impelled to investigate the smell of any unknown buck intruding on his territory.

Hormones

Estrogen in the urine of a doe signals sexual readiness to bucks. Bucks readily respond to estrogen, or other scents that are present when a doe is in heat, soon after they shed their velvet through the second and possibly the third estrous, which may occur as late as January, even in northern latitudes. Because bucks are curious estrogen can be used anytime of the year to attract them.

High amounts of testosterone in urine signal a buck's sexual readiness to does and dominance to other bucks. Testosterone may attract does to a particular area, in turn attracting bucks because the does are there. In one study from the University of Georgia buck urine attracted deer better than estrous urine.

Does travel extensively when they are in heat, often traveling outside their core areas, possibly in search of healthy dominant bucks to breed with. It has been suggested that does can determine the physical health of the buck by the amount of protein in its urine. The doe chooses the buck she breeds with, possibly by the combination of the protein, testosterone and tarsal from rub-urination. I've seen does wait in the vicinity of a scrape of a dominant buck until he showed up.

Lunar Factors and the Rut; The Real Truth

Several outdoor writers believe they have found a way to predict the peak of the rut by using moon phases. One writer believes that the rut will begin 5-7 days after the second Full Moon after the fall equinox, which occurs on September 21/22. He believes that the peak of the rut will occur during the New Moon. Two whitetail researchers, who also write, believe the rut will peak during the Full Moon and Last Quarter of the moon. Another writer believes that the peak of the rut will occur 5-7 days before the first New Moon following the second Full Moon after the fall equinox. What they are all saying is that peak breeding will occur somewhere between the Full Moon and the following New Moon. That would mean the peak of the rut would normally occur before the New Moon in November.

There are several reasons why the "5-7 days before the New Moon" theory may not hold up. The main reason is because the study was based in part on a study of Water Buffalo in India. While the theory may apply to Water Buffalo in India, deer biologists are quick to point out that Water Buffalo are not deer, but a form of cattle. Several researchers also point out that the tropical weather conditions in India are far different from the temperate conditions of North America.

There are two basic problems with these theories. One is that they are so new that they have not been thoroughly tested or proven yet. The other is that they each predict a slightly different time frame. One theory suggests that the peak of the rut will occur before the New Moon, one suggests that the peak will occur during the Full Moon and Last Quarter, and yet another suggests that the peak of the rut will occur 5-7 days before the New Moon. They can't all be right, yet it would be hard to say that any of them are wrong, because peak breeding in many areas usually lasts from 2-3 weeks. The chances are those 2-3 weeks would include portions of both the Full Moon and the New Moon, and everything in between.

One thing that must be made clear is that all of the breeding activity does not occur during the one to two weeks of the peak of the rut. Larry Marchinton's studies in Georgia, and my own studies in Minnesota, show that the breeding season often lasts 90 days or more. While the peak of the rut may occur in November, these studies show that from 10-20 percent of the does may be bred in October, 40-60 percent in November and another 20-30 percent in December; depending on the area, buck to doe ratio, the health of the deer, and the age structure of the herd. In Marchinton's study the 1 1/2-year-old does came into their first estrus in October and November. In most northern areas 1/2 year old does come into their first estrus in December. Generally speaking, in northern areas, the November primary rut will last three weeks, with the peak of the breeding occurring from one and a half to two weeks after the first doe comes into estrus in November.

Melatonin

The theories about breeding activity and the moon involve lunar light, melatonin and reproductive hormones. Melatonin is believed to be a regulator of hormones, and as such it may have the ability to affect the growth and shedding of hair, and affect estrus cycles. It is believed that melatonin is produced during the dark. Because melatonin regulates the production of hormones, some of the writers/researchers feel that a reduction in melatonin during the full moon triggers breeding activity. Supposedly, it takes a few days for the reduction in melatonin levels and the corresponding rise in reproductive hormone levels to occur. Then supposedly, peak breeding activity occurs 5-7 days after the full moon. However, the effects of low light conditions that affect the rutting period of white-tailed deer are thought to be in relation to the reduction of solar light, or daily photoperiod, during the fall; not the increase of lunar light.

To check the validity of this theory I spoke to several well-respected deer researchers. Dr. Valerius Geist says he does not believe there is a correlation between melatonin, moon phase and estrus cycles. He doesn't believe there is enough light during the full moon to affect overall monthly melatonin production. He also agrees (with me) that the prevalence of clouds during the fall would eliminate most of the lunar light during the full moon. Dr. Karl Miller does not believe there is a correlation between moon phase and whitetail estrus cycles either. He told me that in their tests with melatonin that the deer grew winter coats earlier than they normally would, but the average first estrus dates did not change. This suggests that melatonin is not the only thing that controls estrus dates.

Estrus Cycles

These theories may be based, in part, on the misconception that the estrus cycle of whitetails occurs every 28 days, which coincides with a 28-day lunar cycle. However, neither the moon nor a whitetail deer has a 28-day cycle. It actually takes the moon 29 days, 12 hours, 44 minutes and 2.8 seconds to orbit the earth once; and not all whitetails come into estrus every 28 days. Studies by Dr. Larry Marchinton in Georgia show that whitetail does come into estrus from 21 to 30 days, not every 28 days as previously thought. Therefore, even if the first estrus of a doe fell on a specific moon phase during one month, the second estrus could be as much as a week before the same moon phase a month later. I mention the first estrus because several studies on whitetail deer and other hoofed animals suggest that females experience a silent, or non-estrus, ovulation prior to having their first estrus ovulation. If this is true, and the moon phase does affect the ovulation cycle of deer, then the first "estrus" of the doe may not occur during the same moon phase a month later, because the doe may not come into estrus exactly 28 days later.

Photoperiod

The amount of light that affects the rutting period of white-tailed deer is thought to be in relation to solar light, not lunar light. Most deer biologists believe it is the decreasing number of hours of daylight during the fall (referred to as photoperiod) that triggers the rut in white-tailed deer. In northern regions above the 40th parallel whitetails generally breed when there are 9 1/2 to 10 hours of light per day. This photoperiodic change occurs once every year, roughly every 365 days, and so does the rut. But, the rut for deer herds in different areas may vary by days or weeks.

Fawn Survival

The time of year when whitetails breed in each area is dependent on the survival rate of the fawns in the spring. Spring fawn survival depends on weather conditions that are warm enough so the fawns won't die from exposure, and on the availability of spring forage, so that the does have enough to eat to produce milk for the fawns. Through trial and error, and selective survival over several generations, the deer in each area have adapted their breeding schedule so that they breed approximately 200 days before the arrival of spring in their area. To ensure that at least some of the fawns survive each year not all of the does breed, or produce fawns, at the same time. An extended fawning season ensures that some fawns will live even when there is a late spring. Because of this, the length of the breeding season in most deer herds lasts six or more weeks, which makes it hard to predict when peak breeding occurs, especially if it is in associated with the phase of the moon.

Peak Breeding

The rut in most northern areas above the 40th parallel occurs from 180 to 210 days before spring warm-up and the emergence of new growth in that area. However, spring conditions occur at different times in different areas, and so does the rut. Because spring and summer last longer below the 40th parallel, southern deer are able to breed over a wider range of dates than northern deer. Peak breeding on Blackbeard Island off the Georgia coast occurs from mid-September to mid- October, while peak breeding for southern mainland Georgia occurs from mid-October to mid-December. Peak breeding dates in different areas of Louisiana and Texas range from as early as October 15 to as late December 15. Peak breeding in many of the northern states occurs in mid-November.

If you want to know when to expect bucks to be acting stupid during the day, and you want to know when peak breeding activity occurs in your area, check my Rut Dates Chart, it has peak breeding dates for every state where whitetails are found, or you can call the local game managers and ask them. Then you can hunt the two weeks before the breeding activity, when individual bucks are most predictable as they make their rubs and scrapes. You can also hunt the two to three weeks of the breeding period, when the bucks throw caution to the wind in their efforts to find estrus does. Or you can hunt the week after peak breeding, when the bucks are trying to find any does that remain unbred.

What You Are Not Being Told

Although I have read several articles on lunar rut theories, what the average hunter is not being told is that does go through what deer biologists call a "silent" ovulation approximately 12 to 23 days before they experience " estrus" ovulation. During the silent ovulation the does ovulate, but there are not enough reproductive hormones present for the doe to conceive and become pregnant. What this means is that, if the moon does influence breeding behavior, and the moon does affect the estrus cycle of the doe, it is the moon phase the month before the doe comes into estrus that starts the process, and there is the crux of the problem.

Let's suppose that the full moon does trigger a reduction in melatonin level, which in turn triggers the first ovulation cycle of the doe (5 to 7 days after the full moon). In much of North America whitetail does are bred in November. That would mean that it was the full moon in October that triggered the ovulation cycle. Remember, does come into a first "estrus" ovulation until 12 to 23 days after their "silent" ovulation. And we have to add 5 to 7 days for the "melatonin effect" to the 12 to 23 days between the silent ovulation and estrus ovulation.

What that means is: IF a doe experienced a silent ovulation 5 to 7 days after the October full moon, and IF she experienced an estrus ovulation 23 days after her silent ovulation, she COULD come into estrus during the November full moon. But, what if she comes into an estrus ovulation 12 days after her silent ovulation? Then she would come into estrus nine days before the full moon. Now remember that the moon theories suggest the doe will come into estrus from 5 days before to nine days after the full moon. It just doesn't add up.

Priming Pheromones and Rut Synchronization

I've already mentioned that whitetail does experience a silent ovulation prior to having a normal estrus ovulation, which is when they can normally be expected to breed and conceive. And I mentioned that it appears there is no correlation between the phase of the moon and peak breeding. We do know that it is the shortening number of hours of light each day that triggers the rut. But, is there anything besides the sun that helps assure that bucks and does are ready to breed at the same time?

Miller, Marchinton and Knox presented a scientific paper in 1987, in which they suggested that the scents left behind at rubs may serve as priming pheromones, and help bring does into estrus when the does come in contact with the scents. When bucks rub a tree they transfer scents from their sudoriferous (forehead) glands to the tree. The scent from these glands has been correlated with a bucks age and probable social status. In other words, does may be able to tell how old a buck is, and probably whether or not it is a dominant buck or not, by the scent it leaves behind at a rub. But, what matters is that when does smell the scents at a rub it may cause them to come into a silent estrus. Since rubbing usually peaks early in the rut (mid to late September in many areas), and because the does don't all come in contact with the scents at the rubs at the same time, many of them may come into a "silent" ovulation in late September early/October, and come into a normal estrus from late October to late November.

Interestingly, during Marchinton's 1985 study the full moon occurred on October 28 and again on November 27, with peak estrous occurring November 9, showing no correlation with the full moon. This lack of a correlation between moon phase and peak rut was to be expected because of the lateness of the November full moon. I suspect that when the full moon occurs too early or too late the rut will occur when it usually does, during mid-November in the many areas.

Even if the amount of moonlight causes does to come into estrous, Marchinton's research shows that not all does come into estrous during a particular moon phase, or even during the same month. As mentioned earlier, Marchinton found that the estrous cycles of does ranged from 21 to 30 days, with an average of 26 days, but the moon phase changes every 29 1/2 days. Therefore, if a doe came into estrous during the full moon in October, and assuming it wasn't bred, it's second estrous could occur as much as a week before the full moon in November; and two weeks before the full moon in December.

The Moon and Rut Related Activities

My studies, research by Kent Kammermeyer, and research by Grant Woods, suggest there is a correlation between increased daytime deer activity and the moon. These correlation's are related to the position of the moon and the earth; the distance of the moon from the earth; the position and speed of the moon in its elliptical orbit; and combinations of these factors. The position of the moon (not the amount of light) during the full moon phase may cause increased gravitational pull; the distance and acceleration of the moon during the perigee (when it is closest to the earth in it's elliptical orbit) may cause changes in magnetics. The independent or combined effects of these two factors appear to increase daytime deer activity.

Because the elliptical orbit of the moon (the time it takes the moon to revolve around the earth) has a 27 1/2 day cycle, and the light phase of the moon has a 29 1/2 day cycle, the full moon and the perigee can occur on the same day, or as much as two weeks apart. This difference in cycle lengths may be the reason why deer movement is high during the full moon in some years but not in others. I suspect that when the full moon and the perigee occur at about the same time (as in 1997) it may cause increased daytime movement of deer.

No one really knows if and how these lunar factors affect deer activity; which lunar factors influence deer activity and how much; or what happens when the perigee and the full moon occur two weeks apart. The key thing to remember is that daytime deer movement (including breeding activity) appears to be highest during the week of the full moon each month. However, hunting pressure, the rut, food availability and the weather can completely override any affect the moon has on deer. My studies show that during November, when both the hunting season and rut are in progress, there was no noticeable peak in daytime deer activity.

Even though we may not be able to predict when peak breeding occurs, there may be a correlation between lunar factors and daytime deer activity. When normal deer activity, caused by the weather, the rut, or lunar factors, occurs during the day, you would expect that rut related activities such as rubbing, scraping and breeding would also occur during the day. Because Dr. Grant Woods has researched several other deer activities I asked him if this assumption was true. Woods says that when lunar forces cause increased daytime deer activity you can also expect rut activity, including rubbing, scraping and breeding, to occur during the day. Incidentally, I found that the Moon Indicator is fairly accurate at predicting when peak scrape activity will occur.