Whitetails 101

Spring has arrived and there is new life in the forest. Abundant rains and warm temperatures have transformed the starkness of winter into a lush green landscape. Almost overnight, the new growth of spring forbs, grasses, and vines provides an abundance of succulent deer forage. It’s a time of plenty for the deer and a chance for them to restore body condition that has declined during the bleak winter months.

The changing seasons and the abundant regrowth has also set the stage for a miracle that will be repeated millions of times over the next few months. Following the frenzy of the rut last fall, does have been carrying this year’s fawn crop. Now, seven months later, it’s time for new life to enter the deer woods.

In response to increasing daylength and the hormonal changes during late pregnancy, a doe’s behavior changes dramatically. Although does are normally tolerant of other deer, particularly during winter, a few days before giving birth she becomes increasingly intolerant of other deer, including her own young from last year. A few days before giving birth, she isolates herself in a small ‘fawning territory’ and drives away all other deer that intrude. At this time of year, it is not uncommon to see yearling bucks and does wandering around alone, or with other yearlings who likewise have been driven away by their mother. For young males, this separation may be permanent, but yearling does likely will rejoin their mothers later in the summer.

An experienced mother typically returns to the same fawning territory that she used in previous years. Research by John Ozoga in Michigan found that mature, dominant does always selected the best fawning sites, and that her daughters from previous years often established fawning territories in adjacent areas. This isolation of the mother and newborn is essential to establishing a maternal bond during the critical imprinting period. Although it appears that a doe will imprint on her fawn after only a few hours, it may take several days for a fawn to become fully imprinted on its mother.

Late-term does appear to be noticeably uncomfortable. About 1 to 2 weeks before birth the udder begins to swell. In our research facility, we have noticed that within a day or two before giving birth does often start pacing and the tail may be held at ‘half-mast’. However, this may be due to the close confinement of other deer and may or may not happen in the wild.

Following a series of contractions, fawns are born feet first with the head tucked between the forelegs. Usually, the doe is lying during the process, but it is not infrequent for a fawn to be ‘dropped’ by a standing doe. The birthing process proceeds quickly. It may take less that 30 minutes from the time the doe lies down until the fawn is born and completely cleaned, although there certainly is a lot of variation among does. A young doe’s first labor is usually more difficult and prolonged than subsequent deliveries. If the doe is carrying twins, the second fawn is born 15 to 30 minutes after the first.

Fawns typically weigh between 5 and 8 pounds. Single fawns generally weigh more than those born as twins, and male fawns almost always outweigh females.

The newborn fawn is covered with amniotic fluid and other membranes, which the doe begins cleaning immediately. Her licking of the fawn can be quite vigorous and her intense maternal attention may even knock the fawn down as it attempts to stand. In a short time, the fawn is clean. Does will consume all traces of these membranes along with the afterbirth. In fact, her cleaning is so thorough that she will often eat bloodstained leaves at the birth site. The primary purpose of this process likely is to help the mother identify the scent of her fawn and to imprint on the fawn. However, this thorough cleaning also helps to minimize odors at the birth site that may be attractive to predators and a host of insects. Consumption of the afterbirth also might help supply the doe with a variety of nutrients during this energy demanding period.

Fawns begin nursing almost immediately. This first nursing bout provides the fawn with a high-protein milk called colostrum. This colostrum is essential to the fawn because it provides the fawn with a variety of antibodies that help it resist disease until it’s own immune system is fully functional.

Fawns are able to stand within about 10 to 20 minutes after birth, but their weak, wobbly legs won’t carry them far. Often the exhausted doe is content to lie still for a few hours after birth and allow the fawns to gather strength and coordination before moving them away from the birth site. Although twins are born at the same site, they are separated after birth and are kept at different bedding sites for their first 3 or more weeks of life.

Very young fawns do not appear to have any natural fear of predators, and may even walk up to humans. If this happens to you, resist the urge to touch or ‘rescue’ the fawn. Rather, just leave it alone - you can be certain that mother is not far away and will be back to care for the fawn as soon as you leave.

THE MAGIC OF DEER ANTLERS

A Year in the Life of the White-tailed Deer | 29 October 2010

School of Forest Resources | University of Georgia

Throughout the summer, while the does are busy raising fawns, bucks are enjoying a life of leisure. Since the end of the rut last winter, bucks have regrouped into bachelor groups and have been rebuilding body condition in anticipation of this fall’s breeding season. At the same time, they’re also growing a new set of antlers – a phenomenon unique among all other mammals. It’s also a phenomenon that has made deer antlers prized as trophies for primitive and modern hunters alike.

The antlers that are grown by male members of the deer family (and female caribou) are true bones. This is different from the unbranched horns of cows, goats and sheep that are composed of keratin, a protein similar to the hooves. While growing, antlers also have a blood and nerve supply. However, the most amazing thing about antlers is that they are grown anew each year, making them the only mammalian appendage capable of being replaced annually.

Biologists have long debated how and why deer developed these appendages. In fact, antlers seem so improbable, that the thought of an animal that grows sharpened bone daggers from its head each year would seem beyond the imagination of even science fiction writers. But here they are, and clearly they are used in competition among males for mates. Antlers are used in scent marking, dominance displays, and in particular for sparring and fighting.

The seasonal cycle of antler growth and shedding is under the influence of testosterone, but myriad other hormones have been implicated in regulating antler growth. Growth of antlers coincides with long daylengths when testosterone levels are at their yearly minimum. At this time of year, bucks are quite docile and very tolerant of one another. Shortening days (actually longer nights) toward the end of summer result in a stimulation of the testes. The resultant rise in testosterone causes the final mineralization and maturation of the antler, and finally the death and shedding of the antler velvet. Interestingly it is this same rise in testosterone that stimulates muscle growth in the buck, and ultimately transforms him into what researcher John Ozoga calls “a hormone-charged weapon, wielding an awesome mass of muscle – a totally unpredictable beast of amazing strength, stamina, and determination”.

In white-tailed deer, antler growth begins sometime during April or May. Unlike horns which grow from the base, antlers grow from the antler tip. Early growth is slow, but accelerates toward early summer when the antler may grow up to a quarter of an inch in length per day. The growing antlers are highly vascularized, and are quite warm to the touch. Because they are rather fragile, bucks are very careful with their growing antlers. Abundant nerves in the antler velvet allow the buck to know the size and shape of the antler. Rarely does a buck bump his antlers into trees or other objects. They seem to have an uncanny ability to weave their way through brush, fences, and other objects without damaging the tender antlers. The nerves in the antler velvet must be quite sensitive to touch, as even tame deer will rarely allow someone to touch his antlers for very long.

The nerves are also very important in determining the shape of the growing antler, and it appears that there is a ‘trophic memory center’ in the brain that will cause a deer to maintain the same general antler confirmation from year to year. If an antler is injured during the growth stage, the antler may heal but be abnormally shaped. Interestingly, in subsequent years, that injury may be ‘remembered’ and the next year’s antler may show some degree of abnormality. However, if the antler is broken after antler growth is completed, subsequent antlers will very likely be normal.

By the end of July or perhaps early August, antler growth is essentially complete. Amazingly, whether it’s a short spike antler or a Boone and Crockett, all antler growth is essentially completed in about 100 days. This rapid growth places a physiological drain on the buck. Antler bone is composed primarily of calcium and phosphorus, and these minerals either must be supplied in the diet or mobilized from the deer’s skeleton. Throughout August until the velvet is shed, all that remains is the final mineralization of the completed antler.

In most parts of Georgia, velvet is shed sometime toward the last week of August through mid-September. Typically younger deer shed velvet later. Similarly, unhealthy or poorly-nourished deer will also shed velvet later.

Velvet shedding occurs quickly in most deer. Mature bucks may completely shed their velvet in 24 hours, and some may complete the process in an hour or two. Often younger bucks take a little longer to completely remove the velvet. Again, unhealthy deer may take longer to shed velvet, and some may retain shreds of velvet on the antler for some period of time. Often deer will eat the velvet as it is shredded off the antler.

Following shedding of the velvet, the mature antler is essentially dead bone, although there remains some living connection to the deer’s skull which allows for a very limited amount of fluid movement. This helps to maintain a high resistance to impact and prevents the antler from drying out and becoming brittle. In addition, the antler is not composed of solid bone. Except for the antler tips, the antler has a central core of substantia spongiosa (spongy core) surrounded by the substantia compacta (compact sheath). This sheath of compact bone surrounding a spongy core acts to increase the moment of inertia of these antlers compared to antlers of the same weight but composed entirely of compact bone. In other words, ounce for ounce, antlers with a spongy core will have greater strength than solid antlers.

Following the rut, antlers are cast in response to diminishing testosterone levels. Most antler casting occurs in January and February, but well nourished animals may keep their antlers longer. In addition, a prolonged rut may keep bucks in rutting condition longer thereby maintaining elevated testosterone levels, and causing delay in antler casting. In some of our studies of captive deer, we’ve noticed that the larger, dominant deer tend to be the first to cast antlers. Whether this is the case in the wild is unknown, but certainly the health and condition of the buck will be an important factor. A ‘rutted-out’ buck who has spent the last couple of months fighting and chasing does would seem a good candidate to cast antlers early.

WINTER IS ANTLER CASTING TIME

30 October 2010

School of Forest Resources | University of Georgia

Last fall, they were weapons of critical importance in the competition among bucks for breeding privileges. Now, with the rut over, they’re nothing more than useless, dead bones sticking to the buck’s head, waiting to be cast so the antler growth process can start over again. But what causes antlers to be cast? When does it occur? And why do some deer seem to drop early while others carry antlers into late winter or perhaps even early spring?

The first two of these questions are pretty easy, and researchers across the country have provided some clear answers. However, the last question is largely unanswered, although we do have some pretty good guesses.

From the time of Aristotle, and perhaps before, it has been known that the cycle of antler growth, maturation, and casting were somehow tied to the buck’s testes. We now know that a complex mix of hormones influences the antler cycle, but the most important regulator is testosterone, which is produced in the testes. High levels of testosterone in the blood cause the maturation of the antler and it’s maintenance throughout the rut. However, following the rut, testosterone levels begin to fall, and it is this decline in testosterone that ultimately leads to casting of the antler.

Although some writers in the early 1900’s have suggested that bucks may promote casting by thrusting their antlers into the mud or knocking them against trees, it is clear that bucks are quite unaware of the impending event. The falling antler may even startle them.

Often a buck drops both antlers on the same day, sometimes only minutes apart. More rarely, he may carry one antler for a week or longer. Any researcher who works with deer knows that up to a few days prior to casting, the antlers are firmly attached. In fact it may be almost impossible to dislodge an antlers on one day, and then have the antlers ‘pop off’ on their own only a couple of days later.

The process through which antlers are cast actually resembles a type of self-amputation. In response to declining testosterone levels, specialized cells called osteoclasts become activated. These cells specialize in bone resorption, and literally eat-away the bone at the base of the antler. The roughness, or bumpiness, of the base of a cast antler is due to the action of these cells. The base of a freshly cast antler normally is bloodless, although the pedicle from where it detached may become reddened with blood before it scabs over. Almost immediately, a layer of skin starts to grow over the pedicel from the outer edges, and within a week or two the pedicel is completely healed over and waiting for the start of new antler growth.

In most cases, the abscission layer forms at the base of the antler where it joins the pedicle. However, I have noticed several occasions where these abscission layers have formed further down the pedicle, and as a result, part of the pedicle bone, or in some cases part of the cranium itself, were cast with the antler. These unusual occurrences often are due to some type of injury to the head (typically due to fighting) that results in cranial abscesses. However, other injuries that result in rapid loss of condition and rapid declines in testosterone levels may lead to these abnormal casting patterns.

Most antler casting in Georgia occurs in January and February, but some bucks may keep their antlers longer, perhaps as late as late-March. Some of the differences in casting dates likely are due to differences in timing of the breeding season in different parts of the state. However, even within a region there can often be differences in casting time among individuals. It is here that our understanding of factors leading to the timing of antler drop becomes cloudier.

From our studies, we know that individual bucks tend to drop antlers at about the same time each winter – provided conditions don’t change. However, changes in social status or nutritional condition can affect the timing of antler cast. In northern areas of the United States where the period of antler casting is early and relatively short (from mid- December and to late-January), older, larger, and presumably dominant bucks cast antlers earlier than their subordinates. In these areas the rutting period is intense, but short, and bucks leave rutting condition early in ‘anticipation’ of harsh winter weather. Interestingly, some studies in northern states have indicated that the timing of antler casting can be delayed by providing high-quality supplemental forages. Apparently an intense, stressful rut combined with increased food limitations during winter cause a rapid decline in body condition in northern bucks. Testosterone levels drop early, particularly in rut-stressed dominant bucks, resulting in early antler drop.

In Midwestern states, where antler casting extends from January to late-March, whitetailed bucks with large antlers generally retain them longer than bucks with small antlers. Similarly, in Mississippi, researchers have reported that antler casting peaks from February to April and that small-antlered bucks cast antlers earlier than large-antlered ones. Our studies in the University of Georgia Deer Pens indicate a very strong relationship between dominance status and order of antler casting, with subordinate bucks casting antlers before dominant animals. Age of the bucks did not appear to be a factor.

So, why do dominant deer in the South tend to keep their antlers longer, in contrast to Northern deer? Likely the difference is related to differences in the length of the rutting period as well as differences in winter nutrition. In the southern states, it is not uncommon for some does to come into estrus after the peak of the breeding season. Some does may not have conceived during their first estrus cycle and others may just be naturally late breeders. Those female fawns that become reproductively active during their first year also tend to breed later than mature does. Therefore, a few late-breeding does would keep bucks in rutting condition. In addition, winter nutritional stress in many areas of the South is much less severe than in northern states, so bucks can maintain body condition throughout the winter. Both of these factors will allow bucks to maintain elevated testosterone levels, which will in turn delay antler casting.

Hunting for shed antlers can be an enjoyable way to spend a late winter day and can double as a scouting trip for the upcoming turkey season. Every cast antler is a sure indication of a buck that survived the hunting season and likely will be bigger next year. If you plan to hunt for sheds, timing is critical. Perhaps the best time to look is during late-March when nearly all bucks have shed, but spring green-up has not yet hidden the cast antlers.

WHAT’S ALL THIS RUBBING ABOUT?

A Year in the Life of the White-tailed Deer | 31 October 2010

School of Forest Resources | University of Georgia

Rising levels of testosterone circulating in the buck’s blood toward the end of summer have caused the final maturation of the antler and the death of the antler velvet. In only a matter of days, the velvet covered antler is transformed into a polished weapon of competition. These rising testosterone levels (which will continue to rise until levels peak during November) result in a number of physiological and behavioral changes that prepare bucks for the competition for breeding privileges. Whereas bucks during the summer tend to be somewhat docile creatures content to ‘hang out’ with the guys within a fairly small home range, anticipation of the upcoming breeding season literally get ‘in their blood’. Metabolism changes and muscle mass increases, particularly in the neck and shoulders. Sperm production increases. Behaviorally, bucks become more aggressive and increasingly intolerant of each other. Brief sparring matches begin to occur as bucks try out their new headgear, and test the strength and will of their future opponents. Activity of certain scent glands increases and bucks begin to make their presence known to other deer in the area. And, as a result, buck rubs begin showing up in the deer woods – to be followed later by scrapes.

Originally, hunters and biologist alike proposed that rubs were made primarily by bucks cleaning the dried velvet from their antlers. Others have suggested that rubs are made by bucks while mock fighting with a small tree, or that rubbing served to strengthen the neck muscles in preparation for later fights with other bucks. Although all of these may play a role in antler rubbing, we now know that buck rubs serve a much more important role. Studies over the past two decades at a variety of universities, including The University of Georgia and Clemson University, have clearly demonstrated that bucks make rubs as visual and olfactory signposts that transmit some type of information to other bucks and does in the area. Anyone who has watched a buck make a rub certainly has noticed that, in many cases, his actions are very deliberate. A buck generally rubs the base of his antlers, and his forehead skin, against the tree. During the process, he often stops to inspect his progress either by smelling or licking the rubbed area.

A number of years ago, Dr. Larry Marchinton and his graduate students were able to demonstrate that some type of scent was being deposited on these rubs. He used trained dogs to identify these scents and found that the dogs could detect a scent on a rub for up to 3 days after the rub was made. A few years later, one of Larry’s students, Dr. Tom Atkeson, found that the forehead skin between the antlers contained an abundance of scent producing skin glands called apocrine glands. These glands typically are inactive during the summer months, but in response to rising testosterone levels, they become increasingly active in the fall. Tom also found that the most active glands were found in mature dominant bucks. The glands were somewhat less active in younger subordinate animals. Interestingly, forehead gland activity also tends to increase slightly in does during the fall.

More recently, one of my former graduate students, Dr. Jon Gassett, conducted a chemical analysis of the volatile chemicals associated with the forehead region and identified 57 different compounds. Interestingly there appeared to be marked differences in the chemical composition of secretions among different animals. Because of these differences, it is interesting to speculate that bucks may be able to identify which rubs are made by different deer. This suggestion is supported by the observation that following a sparring match between two bucks, the ‘loser’ or subordinate animal will frequently lick the forehead region of the dominant animal.

Early research suggested that most antler rubs were made during the pre-rut in September and that rubbing activity decreased as the peak of the rut approached. However, these studies frequently were conducted in areas where the deer were hunted – which means that the number of bucks in the population was decreasing through the study. More recently, Larry and I directed a study of the rubbing activity of bucks on an unhunted area in Clarke County, Georgia. In that study, the number of new rubs that were made each week remained relatively constant from early September through the peak of the rut until early December (Fig. 1). Significant scraping activity didn’t start to occur until at least a month later.

The number of rubs on any piece of property is influenced by a number of factors. In our studies, we have recorded rub densities that range from less than 500 rubs/mi2 to over 3,000 rubs/mi2. Obviously, one would expect that deer density (or at least buck density) will have a major influence on the number of rubs made on an area. However, while our studies have indicated that density has an impact, it is not a direct relationship. Rather, we have found that the number of rubs is more directly correlated with the density of older bucks (2.5+ year old) in the population. Researcher John Ozoga found similar results in his studies in Michigan. John’s studies revealed that younger bucks make fewer that half as many rubs as did mature bucks, and that they tended to start rubbing much later in the fall. Therefore, because young bucks make few rubs in September or early October, an abundance of rubs during this pre-rut period will generally reveal the presence of an older buck in an area.

Our studies have also indicated that the number of rubs on an area may shift from year to year, depending on food availability. In the north Georgia Mountains, we recorded more rubs in years of good acorn production than in poor mast years, even though buck density did not change appreciably between years.

So, how many rubs will a buck make during the breeding season? That’s a very difficult question to get an answer to, but we can make some quick calculations based on our estimates of rub density and buck density over a number of areas. From our studies, it appears that, on average, a buck may make anywhere from about 400 to over 800 rubs in a breeding season. If we acknowledge that yearling bucks make approximately 50 percent as many rubs as older bucks, our data suggests that on some area, older bucks may be making more than 1200 rubs during the roughly 90 day rubbing period. That translated to about 15 rubs per day!

So, what is the purpose of all of these rubs? We’ll never know for certain because we can’t get inside a deer’s head, but clearly there is some important information being passed among deer. Rubs certainly let other bucks know who is in the area. In addition, because dominant bucks tend to make many more rubs than subordinates, it is likely that dominant bucks mark their normal range with rubs that serve as signposts to advertise their presence and to announce their dominance.

Observations by Dr. Grant Woods while conducting his doctoral research at Clemson University suggest that certain types of rubs may serve special purposes. These ‘traditional rubs’ as he called them, were larger diameter trees that were rubbed in successive years. Grant only found these types of rubs on areas having an older age structure among the bucks. In an attempt to understand the role these traditional rubs play in deer communication, he used automatic cameras with infrared sensors to record any deer that approached these traditional rubs. Although he recorded some instances of investigation of these rubs by does, Grant found that numerous bucks interacted with these traditional rubs, either by smelling the rubbed area or by rubbing on the exposed area themselves. What role these traditional rubs play is still somewhat speculative, but clearly they are important in communication of presence or status among bucks. Certainly we have a lot more to learn about why bucks make antler rubs. But for the deer hunter, antler rubs make one thing very clear – there is a buck in the area! But perhaps more importantly, the knowledge that mature bucks make more rubs, particularly early in the season, means that pre-season scouting can be critical for deer hunters seeking to harvest a mature animal.

Figure Caption:

Temporal distribution of buck rubs and scrapes along with known conceptions dates in a research forest in Clarke County, Georgia.

A COAT OF MANY FUNCTIONS

A Year in the Life of the White-tailed Deer | 1 November 2010

School of Forest Resources | University of Georgia

Spring is in the air, and it’s time to put those heavy winter jackets and camouflage coveralls away and pull out the shorts and t-shirts. Out in the woods, deer likewise are changing their attire from the dark-colored heavy winter coat to a lighter, reddish summer coat.

While you’ve been out scouting or hunting during turkey season, you’ve probably noticed that the deer you saw were looking kind-of ragged and unkempt. They no longer have that sleek, well-groomed look. Instead, the coat looks patchy and often there are areas of hair standing up in all directions, just like my two sons when they get up in the morning. The coat that they’ve been carrying for the past 7 months or so is starting to show the signs of wear.

Molting typically begins on the head and progresses down the neck to the chest and the sides. The haunches and hind legs are the last to shed the winter coat. The entire process occurs fairly rapidly over the span of just a few weeks, although the condition of the deer can affect the timing and the rate of molting. Deer in good condition will tend to molt earlier and faster than those in poor condition. Apparently the shedding hair itches, and deer spend a lot of time grooming themselves, or each other, which partly accounts for the patches of hair sticking up.

The whitetail’s summer coat is much different than the coat it replaces. The summer coat has no underfur and only thin, short guard hairs. These hairs are straight, solid, and about an inch long. The bottom portion of the hair closest to the skin tends to be gray, although the majority of the hair is reddish. In his book The Deer of North America, Leonard Rue reported that there are about 5,000 or more hairs on each inch of a deer’s summer coat, which translates to over 6 million hairs on an adult deer! Deer have very few sweat glands, so they are unable to keep cool by evaporative cooling as we do. Instead, these short thin solid hairs on the summer coat allow air movement and enable deer to keep cool through simple air convection.

Whitetails keep their summer coat for about 4-5 months before they shed again into their winter coats. While the summer coat provides protection from the sun and helps keep the deer cool, the function of the winter coat is to insulate against the cold. Therefore, the winter coat is much different than the summer coat. The guard hairs are a little more than twice as long, thicker, and tend to be ‘kinkier’ than the sleek summer guard hairs. They are also hollow, and this trapped air provides excellent insulation. Surprisingly, there are only about half as many guard hairs on the winter coat than the summer coat – about 2500 to the square inch, but they are twice as thick. The winter coat is gray or dark brown with reddish-brown tips, although some black-tipped hairs are scattered throughout. The darker color absorbs more solar energy, and may help reduce energy expenditure during winter.

Although the coarse, hollow guard hairs of the winter coat provide good insulation, it is the finer, wooly underfur that provides the greatest insulative value. These shorter, finer, twisting hairs trap layers of warm air close to the skin. Although finer, these underhairs are much more numerous than the guard hairs. There may be five times as many. However, it seems to me that deer in more northern regions have much denser amounts of underfur than deer in the South, as you would expect. The long guard hairs coupled with the thick underfur provide such good protection against the cold that snow can accumulate on a deer’s back without melting.

Deer can further increase the insulative value of their fur by ‘puffing out’ their hair. Each hair shaft is attached to a tiny bundle of muscles called arrector pili muscles. In response to cold, the muscles contract causing the hair to stand on end – exactly what happens when humans get ‘goose bumps’. This erection of the hairs results in a thicker layer of insulation and helps deer maintain their body temperature even in extreme cold. As anyone who as ‘fallen in’ while duck hunting can attest, a wet coat doesn’t have much insulating ability. To help keep dry, deer manufacture their own water repellent. Associated with each hair follicle is a small gland called a sebaceous gland that secretes an oily or greasy material called sebum. This oil then coats the hair to keep it from becoming brittle and also help shed water. Interestingly, these are the same type of glands that underlie the tarsal gland and help hold the scent deposited there during ruburination. However, the sebaceous glands in the tarsal region are much larger than those in other regions of the body.

According to George Bubenik, a Canadian deer researcher, nursing does often keep their summer coats longer than bucks and mothers that have already weaned their fawns. He suggests two reasons for this. Lactating does maintain higher levels of a hormone called prolactin, and it is declining levels of this hormone, coupled with other hormones that are influenced by changing photoperiod, that cause the deer to molt. In addition, lactation is energetically very demanding on a doe, and so is molting, so it is difficult to do both at once. According to Bubenik, an adult buck may grow 3 to 4 pounds of hair with each molt. Growing that much hair in a short period certainly places some additional demands on a deer’s metabolism.

Although thermoregulation is the primary function of a deer’s pelage, it plays other significant roles as well. Deer use their pelage for social communication (like the warning alarm of the white tail), as well as camouflage. Varying shades of brown along with patches of white hair on the belly and neck help break up the outline of a deer. The white under the belly also counteracts the shadow cast by the body and helps to prevent a predator from seeing a 3-dimentional animal, particularly in a forested area. Similarly, the white and dark markings on the legs mimic the suncast and shade on a shrub or sapling.

Oddities in hair coloration also occur. Piebald deer are the result of a recessive genetic characteristic and often have varying amounts of white marking that may range from extra white on the legs to an almost pure white coat. These deer also typically have other deformities such as short legs, a curved spine, and a Roman nose. Pure albinos are much more rare. These deer lack the ability to produce the pigments that color the hair, and will always have pink eyes and a pink nose. Rarest of all is a melanistic, or pure black, deer. Perhaps you’ve seen pictures of the black buck that was killed in Pennsylvania last fall. Although extremely rare, these black deer are reported every few years. However, probably the most interesting part about these black deer is not their color, but the fact that they often have a short, stiff mane of hair running from the back of the head to the shoulders.

HOW WELL DO DEER HEAR?

A Year in the Life of the White-tailed Deer | 2 November 2010

School of Forest Resources | University of Georgia

So, just how good are a deer’s ears? Can they hear your muffled cough at 200 yards? Can they hear those deer whistles that you put on your truck?

Trying to understand how well a deer hears (or sees, or smells) is an extremely daunting task. We can’t just ask them “Did you hear that”?, so instead we have to rely either on behavioral observations or some type of advanced technology. Thankfully, in the past few years, there have been a couple of research studies conducted that can give us a good idea of how a deer hears.

However, before we get to these studies, let’s think about the structure of the deer’s ears. The large external ears (or pinnae) of the deer work somewhat like a satellite dish. They help to amplify the sound (just like cupping your hands behind your ears), but because they can move independently of each other they also help the deer evaluate what is happening in all directions. We’ve all noticed how deer continually shift the direction of the ears, and simply by watching the ears a hunter can get a good idea of what the deer is thinking. When traveling together, deer often keep track of each other by listening. So, if you see a lone deer, watch its ears! If it frequently cups one or both ears to the rear, you have a good bet that there is another deer following.

Similarly, if a deer is looking directly at you, don’t be too concerned if its ears are moving in different directions. However, if it has both ears cupped toward you – you’ve been spotted and he’s trying to get all of the information he can. By comparing the signals that each ear receives the deer can accurately locate the source of a sound.

All hunters have stories that point to the acuity of a deer’s hearing ability: “I just lightly bumped my bow on the stand and that guy just bolted!” or “I couldn’t believe how smart that buck was! He heard me click off the safety at 75 yards!” But let’s put this in perspective. Deer live in the woods 24 hours a day, 7 days a week. It’s their home. They know what sounds are normal there, and what sounds are not. They’ve heard those sounds all their life. So the crashings of a grey squirrel through the leaves or the rustle of a brown thrasher in a hedgerow are barely noticed. But the unnatural cadence of a human’s walk or a ting of metal-on-metal is instantly identified as foreign and raises suspicion. It’s just like in your home or office. Certain noises are ‘normal’, but something different or unusual is instantly identified as abnormal.

But still the question remains - is a deer’s hearing better than ours? With the large external ears you might expect this to be the case. However, two recently released studies cast some doubt.

A couple of years ago, David Osborn and Larry Marchinton here at the University of Georgia discovered an unpublished study by Mr. Arthur Stattelman who researched the hearing capability of deer confined to a sound-proof room. They compiled the data from this research and reported some interesting results. They described the study as follows: “The deer was conditioned to seek and accept food whenever it heard a sound. A machine called an audiometer was used to create a wide range of sounds varying in intensity (loudness as measured in Decibels) and frequency (tone as measured in Hertz). The intensity at each frequency was increased until it produced a positive response from the deer. When repeated over time this procedure provided some understanding of what sound the deer was able to hear. The results of the experiment are presented (in the accompanying graph) and are compared to some common sounds and the minimum hearing capability of humans and the domestic cat. Deer and humans apparently can detect sounds of low-to-moderate frequency at approximately the same intensity. A cat can hear much fainter sounds than either the deer tested or humans across a wide range of frequencies. Deer probably detect high frequency sounds slightly better than humans. These findings may shock many hunters who have formed opinions about the hearing ability of deer based on personal experiences”.

Dr. Kenneth Risenhoover at Texas A&M University, who used some sophisticated technologies to generate audiograms for 5 adult deer, recently substantiated this research. His results were very similar to those from the Georgia study: “Evoked potentials (responses) were detected and recorded at intensity levels of up to 85 dB in a frequency range of 0.5 to 12 Khz. Evoked potentials from the 5 deer tested indicated that the range of greatest hearing sensitivity was between 1 and 8 Khz, with a marked peak centered at 4 Khz.”

This research all seems to indicate that a deer’s hearing is really not that more acute than ours. They are not like the $6 Million-Dollar Man (or was it the Bionic Woman?) who could hear the bad guys whispering at a quarter-mile. Instead, a deer knows you’re in the woods simply because you are making some noises that aren’t supposed to be there!

Oh, and about those deer whistles for your truck - Based on the research at Texas A&M and at the University of Georgia, it seems very unlikely that deer whistles would be effective at reducing deer-vehicle accidents because the high frequencies produced appear to be out of the hearing range of deer. And besides, why wouldn’t they just be able to hear your truck even without a whistle?

THE ROLE OF THE SCRAPE

A Year in the Life of the White-tailed Deer | 3 November 2010

School of Forest Resources | University of Georgia

While antler rubs are pretty simple signposts that involve only scent from the forehead glands, a scrape involves several scent sources and probably has multiple functions in deer communication and reproductive behavior.

Despite years of research by wildlife biologists, there is a tremendous amount that we don’t know about scrapes. However, in recent years we have made some important steps toward understanding who makes and visits scrapes, when they are made, and what types of information is transferred at scrape sites.

Scraping typically begins with a buck approaching a branch hanging just above his head. The buck often mouths the branch and rakes it with his antlers. Judging from the buck’s behavior, marking the overhanging branch appears pleasurable, and he sometimes seems almost oblivious to his surroundings. Clearly, the buck is leaving some type of scent on this overhanging branch, although the exact source is still ambiguous. Likely the forehead gland is involved in marking the limb, but other potential scent sources include the preorbital gland, the nasal gland, and even saliva. After the overhead limb is marked, the buck paws away the leaves directly below the limb, likely leaving scent from the interdigital gland in the pawed area. The area cleared of leaves varies, but typically a 3- foot diameter circle is common. The buck then steps forward and urinates over the tarsal glands while rubbing them together, allowing urine to flow into the pawed area. This urine leaves a persistent strong odor and may stain the soil dark even after it has dried.

Many hunters may not be aware that this full scrape sequence actually is a composite of three separate behaviors that may, in fact, occur independent of the other two. Several years ago we conducted some year-round observations in our research facility and found that the overhanging branches at some of these scrape sites are used throughout the year by bucks of all age classes. We speculated that these overhanging branches serve as a kind of ‘calling card’ to let other bucks know who is in the area. Bucks tend to live somewhat solitary lives, except during the spring and summer when they form bachelor groups. But even then, group membership tends to be somewhat fluid, so having a chemical signpost where bucks can communicate their presence could obviously be important. Since then, our observations of year-round use of these overhanging branches has been confirmed by other researchers. Interestingly, many of these licking-branches become scrape sites during the rut.

Similarly, rub-urination commonly occurs outside of the scrape. While most common and noticeable in bucks during the rut, all deer commonly urinate over their tarsal glands throughout the year. Does ruburinate, on average, about once per day, typically when they rise from a nocturnal bed. Even day-old fawns urinate over their tarsal glands. The scent that develops on the tarsal gland from this ruburination likely carries information on the deer’s identity as well as social and reproductive status. (We’ll discuss this more in next month’s column).

When combined at a scrape site, the three behaviors appear to provide a host of information to any deer visiting the scrape. The overhanging branch provides a clue to who visited the scrape, pawing the ground may signal an aggressive intent and also provide more information in the identity of the scrape maker, and ruburination into the scrape further reveals who made the scrape along with his dominance status.

Although some scrapes may be made as early as September, numerous studies have repeatedly shown that the peak in scraping activity occurs two to three weeks before the peak of the breeding activity. For example, in a study directed by Larry Marchinton and myself on an unhunted area in Clarke County, Georgia, scraping activity increased dramatically during mid- to late October (Fig. 1). The peak of conceptions (the peak of the rut) occurred during the first week of November. In that study, our surveys indicated that the density of scrapes was in excess of 300 scrapes per square mile, with the majority of those scrapes made during a 4-week period! Some scrapes in the study were pawed repeatedly for up to 3 consecutive weeks, and many that were not had fresh tracks in them for up to 2 weeks.

The high number of scrapes that we observed in this study certainly was reflective of the unhunted deer population on our site and the presence of a number of older bucks. Several other research studies have also indicated that most scrapes are made by bucks 2.5 years old or older. A study conducted by John Ozoga in Michigan found that yearling bucks made only about 15% as many scrapes as older bucks, and that scraping activity by these yearling bucks typically occurred later in the breeding season.

However, there is some evidence that even mature bucks will vary greatly in the amount of scraping that they do. Age is important, but a buck’s testosterone levels, social position, experience, and behavioral maturity also interact to promote scraping behavior. Some bucks just tend to be avid scrape-makers, whereas others are not. And, according to John Ozoga, competition appears to be important – where there are several mature, rutexperienced bucks working the same breeding range, scraping will be enhanced.

What’s this mean for the deer hunter? First, the presence of scrapes early in the rut certainly is a good sign that there may be a mature buck in the area. Second, a dramatic increase in the number of scrapes provides a strong clue that the peak of rutting activity will occur in the next 2 to 3 weeks (Which means that continual scouting during the hunting season is critical!). And, third, if you are not seeing a lot of scrapes on your hunting area, you might want to consider if you are overharvesting your bucks.

Just because older bucks make the majority of scrapes does not mean that younger bucks will not scrape or at least visit scrape sites. In a 2-year study, 2 of my graduate students (Karen Alexy and Jon Gassett) placed motion-sensitive video cameras over scrape sites to monitor who made the scrapes, who visited them, and when they were visited. The results were fascinating! Like other studies, scrapes were made and visited most frequently in the weeks just before the peak of breeding activity. When the peak of the rut hit, scrape visitation dropped to almost zero. More interestingly, Karen and Jon’s study revealed that scrapes were investigated and marked by a number of different bucks, including yearlings, during the weeks before the rut. Does also visited the scrapes before the rut peak, but not during it.

Because scrapes were visited by a number of different bucks, one might be tempted to think that scrape sites would be excellent places to hunt. However, Karen and Jon’s study also revealed that the vast majority of scrape visits (almost 90%) occurred at night. So, unless you’re hunting past legal shooting hours, you’re going to miss most activity at scrape sites.

So, what’s the purpose of the scrape? Although only the deer themselves and their Creator know the answer to this question, our studies are giving us some insight into the types of information being communicated. Certainly they play an important role in the chain of events that lead up to the peak of the rut. Bucks relay information about their presence and dominance status to each other, as well as their availability to does in the area. In other words, the scrape tends to serve as an extension of the animal itself. Does may use scrapes to help identify and select the best mate, but we also believe that the scents left at scrape sites may play a role in priming the does reproductive cycle and synchronizing estrus among does in the area. This synchronization of estrus is important as it leads to a synchronization of the fawn drop 7 months later, which will help to enhance fawn survival by minimizing the risk of predation.

Figure Caption:

Temporal distribution of buck rubs and scrapes along with known conceptions dates at The University of Georgia’s Whitehall Experimental Forest in Clarke County, Georgia.

MAKIN’ TRACKS

A Year in the Life of the White-tailed Deer | 6 November 2010

School of Forest Resources | University of Georgia

What would be more appropriate for this final article in the “Year in the Life of the White-tailed Deer” series than an article on deer tracks? Tracks certainly are the most important evidence, and sometimes the only evidence, that a deer has been in the area.However, the presence of the track reveals one obvious fact – the track maker has left the immediate area. In other words, tracks can only give us information on past deer activity in the area, but this historical information can be very useful in predicting future movements.

Tracks can provide much more information than simply that a deer has been there. An experienced woodsman can glean other details, such as when the track was made, the size of the deer that made it, and sometimes the sex of the track maker. But before we go into reading tracks, we need to discuss the hooves that make those tracks.

Deer are members of the order Artiodactyla, or the even-toed ungulates. Other members of this order include sheep, goats, cows, and pronghorns. The relatively small size of a deer’s hooves provides minimal contact with the ground, thereby reducing friction and allowing greater speed. The concentrated points of contact also allow for rapid changes in direction.

Hooves are basically modified fingernails, so in essence, a deer is walking on the tips of its toes, much like a ballerina. A deer’s foot actually extends from the joint associated with the tarsal gland to the tips of the hooves. The outer surface of a hoof is made of a highly keratinized material and is quite hard. The sole, in contrast, has a softer, spongy surface that provides good ground contact. The two parts, or toes, of a deer’s foot correspond structurally to our middle and ring fingers, while the dewclaws behind the hooves correspond to our index finger and pinky.

Although you may not notice it at first glance, there are some important differences between the hooves on the front legs and those on the rear. Because they bear more weight, and take more impact when running, the front hooves tend to be slightly larger than the rear, especially in bucks. Front hooves of an average adult buck will be about 3 inches long and 1 ½ to 2 inches wide. In addition, the dew claws on the front legs are much closer to the hooves than those on the rear, which makes it quite easy to tell a rear foot from a front foot.

The deer’s hoof has another interesting adaptation that helps enhance their running and leaping ability. Attached to the hoof is a specialized ligament, called a springing ligament. When the hoof is supporting the deer’s weight, this ligament is stretched tight. As the hoof leaves the ground, the ligament rebounds and the hoof snaps backward providing extra spring to the gait and increasing both the speed and the thrust of the deer’s stride.

Hooves are constantly growing throughout the life of the deer, and the rate of growth appears to be adapted to a normal rate of wear. This means that in areas of soft or sandy soils hooves can become overgrown and may appear long and pointed. However, in rocky, mountainous terrain where abrasion is greater, hooves will tend to be shorter and blunt. Several years ago we conducted a little study at the University of Georgia Deer Pens to determine the rate of growth of deer hooves. We found that, on average, a deer’s hooves grow at a rate of about 2 ½ inches per year, or roughly about 5 millimeters per month. As you might expect, the hooves of younger deer grow faster than those of adults, and hoof growth rate is greater during summer than winter.

Hunters have long debated whether a deer’s sex can be determined from its tracks. The presence of impressions from the dew claws has often been interpreted as a sign that the track maker was a buck. However, there are a number of factors that affect whether or not dew claw impressions will be left, including the dryness and texture of the soil, whether the track came from a front or back hoof, and whether the deer was walking or running. Because of these factors, dew claw presence in the track is not a reliable indicator of sex.

We do know from a number of studies that there are some differences in hoof sizes between adult male and adult female deer, but whether these differences are sufficient to reliably determine a deer’s sex is debatable. Over 50 years ago a biologist and sportsman named Weston argued that “No man, not even the most astute woodsman, can positively and consistently identify the sex of a white-tailed deer by its track alone”. Several years later a group of researchers in California conducted a study of the characteristics of black-tailed deer hooves. Although their results indicated that there were significant differences in both hoof length and hoof width between the sexes of yearling and adult deer, they cautioned that there was considerable overlap in these measurements. This means that in most cases it would not be possible to accurately determine the sex from tracks in the wild.

At the University of Georgia, a student named Pete Swiderek repeated this study by looking at white-tailed deer hooves. He found that, except for the tracks of larger bucks, the sex of a deer couldn’t be determined by measurements of its tracks.

Thus, these studies have demonstrated what many hunters have known all along… a really big track was likely made by a buck, but it’s impossible to tell the sex of an average size track based on size. But there are some other clues besides size. A mature buck’s hooves tend to be more rounded at the tip than a does, particularly the front hoof. However, terrain and soil conditions can influence this as well.

If you’re lucky enough to be hunting or scouting while there is some snow on the ground, there are a number of clues that will help you determine the sex of the track-maker. I spent many-a-day as a youngster growing up in Yankee-land just following deer tracks in the winter to determine what the deer were doing, and these tracks taught me a lot! In particular, I frequently learned about their use of escape cover when the track-maker caught me studying his tracks. But I also learned some aids in identifying the sex of the deer I was following. For example, looking at the size of the tracks of other deer associated with the track-maker is certainly a good clue – small accompanying tracks suggest a doe with her fawns.

Urination patterns also may differ. Both sexes often stop and urinate in one spot, but at times bucks may just urinate as they walk, so a urine trail in the snow is a pretty good clue. Similarly, two tracks close together with urine splashed around them would signal that the deer rub-urinated, a behavior more commonly associated with bucks.

Bucks tend to be lazier than does when walking, particularly during or after the rut. Often, a buck may leave drag marks in a light snow from his front feet, whereas a doe typically won’t.

Despite these clues, however, there is only one way to be absolutely certain about the sex and size of the deer that made a particular track, and that is to find the track while the deer is still in it!

THROUGH THE EYES OF A DEER

A Year in the Life of the White-tailed Deer | 7 November 2010

School of Forest Resources | University of Georgia

You’ve just topped over a little rise, and there he stands – less than 100 yards away. Looking straight at you! You freeze, but you know you’ve been spotted. You know that at any instant he’s going to bolt. But amazingly, after a short while he drops his head and resumes his search for acorns! “Certainly he saw me”, you think, “I see him clear as day. Why didn’t he recognize me as a human? Is he just stupid?”

I imagine that any deer hunter who has spent any time in the woods can relate very similar experiences. Why does it seem that a deer can look directly at something, and still not ‘see’ it? The answer lies in how a deer’s eyes are constructed. A deer’s view of the world is very different than how we see it. Our eyes, and those of a deer, are adapted for very different purposes, and understanding these differences can not only make you a better hunter, but a safer hunter as well.

As prey animals, deer must constantly be on the lookout around them. Their eyes are set on the sides of the head, and protrude slightly from the skull. Although they cannot see directly behind themselves, this eye placement gives a deer a field of vision of about 310 degrees, which would explain how a deer can see a bowhunter draw back even with a quartering-away shot.

Every hunter certainly has noticed that a deer’s eyes are larger than ours in comparison to our relative body sizes. This larger eye allows the pupil opening to be much larger than ours, particularly in low light conditions. A larger pupil opening greatly enhances the light gathering ability of the deer’s eye. In fact, due to the larger pupil opening, a deer’s eye may allow 10 times (or more) light to enter the eye than ours. In addition, like other animals that are adapted for nocturnal behavior such as cats, dogs, and even whippoorwills, deer have a reflective membrane located at the back of the eye. This membrane, called the tapetum lucidum, is what causes the eyeshine of deer caught in an automobile headlight (or spotlight). Light entering the eye passes over the receptive layer of rods and cones in the deer’s retina, and then is reflected back over this receptive layer a second time. Therefore, if a deer’s eye has 10 times the light-gathering ability as we do, and the light passes over the rods and cones twice, it is easy to understand why deer can run through the woods on the darkest nights without crashing into trees.

There are other differences between our eyes and those of a deer. In the human eye, the lens focuses the image on a small circular area of the retina called the fovea. Harpness of vision, and sensitivity to color, depend on the number of cones in this area, whereas sensitivity to movement is more dependant on the concentration of rods. In the human fovea, the number of cones in the fovea may exceed 150,000 per square millimeter, giving us excellent visual acuity. A deer’s retina contains fewer cones in proportion to the number of rods, which likely explains why they have such excellent ability to detect movement.

In a number of ungulates such as cattle and horses, the lens focuses the image on a horizontal band across the retina instead of on a small circular area. This area has a high density of receptors and allows the animal to focus on a horizontal band, instead of a single point like humans. As you might expect, this ability to focus on a wide horizontal band also would enhance the ability to detect movement. Deer likely are similar to these other ungulates. In fact, if you take a close look at a deer’s eye during daylight, you’ll notice that the pupil opening is reduced to a side-ways oval, rather than a small circle like in the human eye.

The differing proportion of rods and cones, along with the different focusing mechanism of the lens also results in differences in visual acuity. But attempting to determine just how well a deer can see is a difficult undertaking – they can’t read a doctor’s eye chart very well! However, I have seen the reports of one experiment suggesting that humans have a visual resolution about twelve times better than that of deer.

Unlike deer, humans and other primates are unique in that they have a yellow pigment in their lenses that screens out short-wavelength light to protect our retinas from damaging ultraviolet light. Without this pigment, deer should be more sensitive to shortwavelength light, particularly under low light conditions.

So far, we’ve shown that humans tend to have keener eyesight than deer during the day, but deer are better at discerning movement and have better night vision. But, can deer see colors? This question has been debated among hunters for centuries. We know that deer have cones in their retinas, but possessing cones does not necessarily mean that they can see color.

A few years ago, we conducted a study at the University of Georgia, in collaboration with the University of California, Santa Barbara to conclusively determine if deer had the ability to see in color. Before I describe the study and the results, we first need to review some basic facts about how color vision is produced.

Cones contain different types of materials called photopigments, and it is these materials that produce the ability to see color. Rods only contain one photopigment, which means they can only produce black and white vision. On the cones, color vision is produced if there is more than one type of photopigment. We have three types of photopigments, each with sensitivities to different wavelengths of light. One has peak sensitivity at the wavelength we call blue, one at green, and the third at red. These are the three primary colors from which we derive all other colors. Although we know that deer have cones in their retina, what we did not know is what types of photopigments are contained on the cones.

In our study, we used a highly sensitive apparatus to record the electrical impulses from the photopigments in the deer’s eye. If we found two or more photopigments, deer certainly should have the ability to see color. Our results indicated that a deer’s eye has two types of photopigments. One of the photopigments was very similar to our blue pigment, while the other peaked in sensitivity in the wavelength that we call yellow. Without going in to too much detail, our study indicated the following:

1) Deer have the ability to discern among some colors, and their color vision likely is somewhat similar to a human with red-green colorblindness. In other words they likely would have a hard time distinguishing between reds and greens, but could distinguish these colors from those in the blue range.

2) Deer appear to be more sensitive to light in the shorter wavelengths – in other words they likely can see blues better than we can, so leave the blue jeans at home! In addition, many detergents have brighteners in them that would be quite sensitive to a deer’s eyes. So, be sure to wash your hunting clothes in a detergent that does not contain these brighteners.

3) Deer cannot see colors out into the red range as far as we can. Dark red would appear black to them. More importantly, deer are not able to see blaze orange with the vividness that we do – a deer’s sensitivity at this wavelength is less than half of a human’s sensitivity. Deer would have a much harder time distinguishing it from the colors of the forest. So there’s no excuse not to wear blaze orange when deer hunting! They just don’t see it the same way you do. Be safe, not sorry!

WHAT TIMES THE RUT?

A Year in the Life of the White-tailed Deer | 8 November 2010

School of Forest Resources | University of Georgia

By the time you read this, the peak of the rut should be pretty much history for most of the state. However, if you should happen to be hunting in the extreme southwestern corner of the state, you can still look forward to a rut peaking sometime in mid-December.

In last month’s issue of GON, Daryl Kirby presented an excellent article on the timing of the rut. Accompanying the article was a map indicating the timing of the peak of the rut in various regions. This map provided some invaluable information to help hunters plan their trips afield depending on where they hunt.

The map also provided some of the clues for a biological riddle that has intrigued biologists and hunters alike for decades. An astute deer enthusiast certainly would have noticed that the peak of the rut across the state can vary by as much as 2 months, and most of this variation is due to the rut occurring progressively later in an east-to-west direction. This trend continues beyond the state borders, with an earlier rut in coastal South Carolina, and a progressively later rut through Alabama, Mississippi and into Louisiana. Interestingly, the rut gets earlier again in east Texas and then progressively later across the Lone Star state.

The riddle here is ‘Why should the rut vary across the state and the Southeast?’ and related to that is the question of ‘What then is the mechanism that triggers the rut?’

If you pose these questions to 10 different biologists, you’re likely to receive 10 different opinions, because we really don’t know the answers. There have been numerous theories proposed which suggest a variety of influences such as a genetic cue depending on the stocking source of the deer, the lunar cue dependent on the timing of the full moon, and the herd age structure and sex ratio. Let’s take a look at these theories based on some scientific data (but liberally sprinkled with my opinion!).

One thing that we know for certain is that in the temperate regions of North America, the breeding chronology of whitetails is primarily under the influence of changing photoperiod. Deer, like a variety of other animals, are short-day breeders. This means that their breeding season occurs at a time when the length of the day is decreasing. Inside the deer’s brain is a gland called the pineal gland that secretes a hormone called melatonin. However, this gland only secretes melatonin under the influence of darkness. So, as nights grow longer, the portion of the day during which melatonin is secreted increases. So, it is in this way that deer can keep a ‘chemical clock’ that tracks the changing seasons. As the duration of melatonin secretion increases, it allows a series of other physiological changes to occur. Testosterone levels in the buck start to increase resulting in maturation of the antlers, shedding of velvet, increased aggression, increased sperm production, and increased interest in the does. Similar things occur in the does, with increased ovarian activity resulting in changing levels of estrogen and progesterone, which ultimately culminate with estrus and ovulation.

In the northern portions of the whitetail’s range, timing of reproduction is critical. Fawns born too early as a result of early breeding would be at risk of a spring storm, or maternal does may not have had sufficient time to restore body condition in the spring to provide sufficient care. Similarly, late born fawns may not have sufficient time to grow and develop sufficient fat stores to allow them to survive their first winter. In addition, photoperiod changes much more rapidly in more northerly latitudes, allowing the melatonin clock to time reproduction more precisely.

In southern ranges, the timing of reproduction is less critical, and fawns born early or late likely would have a greater chance of survival than those born ‘up North’. Photoperiod also changes more slowly in southern latitudes. Therefore, because seasonal climate changes are not as severe, fawns born in central Georgia in late May or early June tend to have about the same survival rates as fawns born in July in portions of Alabama, or even August in Mississippi.

So, although photoperiod is the overriding factor that ensures that breeding in the South occurs in the fall or winter, the somewhat forgiving climate in the southern states allows the timing of the rut to differ among different deer herds. But the questions remain: Why do different deer herds have different rutting periods across the south? and What triggers the rut in the different areas?

Probably the most commonly proposed explanation for the differing breeding dates across the South is that deer herds were restocked in the mid-1900’s with deer of varying origin, and the current breeding dates reflect the origins of these herds. In other words, there appears to be a genetic tie that dictates breeding chronology based on where the deer originally came from.

However, in my opinion, the stocking source theory doesn’t explain all of the trends that we see, and certainly is not well supported by the data. For example, the origins of the deer herds in many Piedmont counties (and other parts of the state as well) were primarily some of the coastal islands including Blackbeard, Ossabaw, and Jekyll. On these islands, most breeding occurs in late September or early October. However, the peak breeding in the counties receiving many of these deer usually falls around early or mid-November. As another example, much of Alabama was restocked with deer originating from Clarke and surrounding counties in the southwestern portion of the state. However, the timing of breeding across Alabama can be highly variable. These and other examples suggest that it is highly unlikely that there is a genetically-tied cue that triggers when the rut will occur. We’ve been able to further substantiate this in our research facility where we have been able to successfully change the timing of when does naturally come in heat, something that couldn’t be done if the timing was based on genetics.

The timing of the full moon in September or October also has been suggested as the triggering mechanism for the rut. Again, this clearly does not fit the data available because moon phase is the same all across the South, and the timing of the rut is very different. In a recent study, we looked at the breeding dates of >2,500 does from 7 states across the United States, and found absolutely no relationship between breeding dates and moon phase.

In a number of studies across the Southeast, the herd sex ratio and buck age structure has been implicated as a major influence on the timing of the rut. Very heavy male harvests with limited doe harvests leads to young male age structure and sex ratio skewed toward females. In areas where a significant portion of the buck harvest occurs early, sex ratios may be even more skewed at the time of the rut. These herd conditions can affect the rut in two possible ways. First, the fewer the bucks to go around, the greater the chances that a female will not conceive during her first estrous cycle. If that happens, she must wait through another complete cycle (about 26-28 days) before coming into estrus again.

In addition, we’ve found that simply the presence of mature males can have an effect on the timing of estrus in females. In a study that we conducted at the Smithsonian Institution, we found that simply the scent of urine from males can have a stimulating effect on the reproductive physiology of females.

Nevertheless, although age structure and sex ratio can have an effect on the timing of the rut on local areas, it still does little to explain why rutting seasons vary broadly across the Southeast.

Thus far, none of the mechanisms that have been proposed (as discussed above) seem to provide a plausible explanation of why rutting times differ. Which leads me to my opinion – deer herds differ in the timing of breeding simply because they can! Let me explain what I mean. We know that changing photoperiod is the primary triggering mechanism responsible for timing the breeding season. However, there may be some small differences in how different deer herds time their reproduction based on photoperiod. Or, stated differently, deer herds differ in how their ‘reproductive alarm clock’ is set. Some may go off in response to photoperiod length typical of October, whereas others may require more hours of darkness (i.e. longer melatonin secretion) before the alarm goes off. However, the timing of the alarm is not set by genetic cues, but rather this timing can be physiologically ingrained in the herd, and passed on from mother to daughter. Studies have demonstrated that there are melatonin receptors in the developing fetus that respond to melatonin levels in the mother. Therefore, it is possible that the melatonin cue may be set in a female while still a fetus. Thus a daughter would be expected to breed at roughly the same time as her mother. In this manner, the timing of reproduction could be passed from mother through successive generations.

Unlike northern herds, environmental conditions are less likely to weed out those individuals that breed at a different time. The possibility of winter mortality is not a significant factor in the Southeast, and therefore does not limit breeding to one specific optimal time. So, deer in Alabama may breed in December or January simply because there is no overriding factor such as winter weather that forces them to breed earlier. And, once this reproductive timing becomes ingrained in the deer herd, there may be little reason to change. Fawns born earlier or later that the ‘normal’ fawning season may be at increased risk for predation or other mortality, so the timing persists.

Whatever the reason for the different rutting periods across the Southeast, there likely is little that we can do to change them. Proper deer herd management may have some minor impacts on the timing and intensity of the rut. But perhaps the best thing we can do is to enjoy the diverse breeding seasons and be thankful that there are still a lot of mysteries about this creature that we don’t yet understand.

A WHITETAIL'S SIGNATURE - THE TARSAL GLAND

4 November 2010

Warnell School of Forest Resources | University of Georgia

When human beings meet, we recognize each other on sight by identifying facial features, or perhaps by voice patterns. Not so with deer! Although deer likely learn to identify some others on sight, deer rely primarily on the sense of smell for personal recognition.

A variety of glands may be involved in recognition of other deer by scent, but clearly the tarsal gland is the most important. Any deer hunter who has harvested a buck during the rut is very familiar with the strong scent that is often associated with this gland. However, few hunters are fully aware of the role that this gland plays in deer communication. Deer often sniff the glands of other deer, particularly deer they are unfamiliar with. The frequency of tarsal gland sniffing appears to be greater at night than during the day, probably because of reduced visibility. By smelling the tarsal scent, deer can not only tell who the other deer is, but they likely can also learn something about the other deer’s dominance status, sex, condition, and other socially important information.

Over the past decade, we have conducted a number of studies at the University of Georgia in an attempt to decipher the role of this gland in deer communication. Although we’ve made some tremendous strides in our understanding, we still haven’t pieced together the entire puzzle. But what do we know at this point?

The tarsal gland consists of a tuft of elongated hairs on the inside of the deer’s hind leg. Each of these hairs is associated with an enlarged secretory structure called a sebaceous gland. These sebaceous glands secrete a fatty material, called a lipid, that completely coats the hairs. The hairs themselves have specially modified scales to provide greater surface area for holding the fatty material. However, based on our research, it is not this material that gives the gland its strong musky odor. Rather, the smell comes from urine that is deposited on the tarsal gland during a behavior called rub-urination. Retaining the odor requires daily ‘recharging’ of the gland with urine.

In one of our studies, we investigated the activity of these secretory glands associated with the tarsal gland. We thought that since bucks urinate on to the tarsal gland more frequently during the breeding season than at other times, the fat-secreting structures would become more active as well. Instead, we were surprised to discover that the activity of these glands did not change during the year, and that there was no difference in the activity between males and females. These results indicate that it is not a change in the activity of the gland itself that causes a change in the smell of the tarsal gland. Instead, the change is smell (and color) comes from a change in the frequency in rub-urination, and perhaps from a change in some of the components of the deer’s urine.

Although all hunters know that bucks urinate onto their tarsal glands during the breeding season, it is less widely known that this behavior occurs throughout the year (although less frequently). In fact, bucks and does will urinate onto the tarsal gland about once per day throughout the year. Even day-old fawns have been observed urinating on their tarsal glands. Does apparently identify their fawns through the odors given off the the fawns’ tarsal glands. Interestingly, bucks will often smell and lick the tarsal glands of an estrous doe as a prelude to mounting.

The skin underneath the tarsal tuft also has well-developed arrector pili muscles, which allow the deer to flare the tarsal gland to release a burst of scent. Deer often flare this gland in response to physical or social trauma – a painful injury or perhaps harassment from other deer.

Any observant hunter certainly has noticed that the tarsal gland smells nothing like the smell of fresh urine. So where does this stink come from? Well, the picture gets a little more complex here. The warm, moist, nutrient-rich tarsal glands provide a perfect environment for the growth of a number of species of bacteria. As the urine runs over the tarsal hairs, the fatty material on the hairs selects out some of the fat-soluable compounds from the urine and holds them on the hair. The bacteria on the gland then change these materials to produce the gland’s characteristic smell.

Recently, two of my graduate students, Jon Gassett and Karen Alexy, conducted a study of the types of bacteria on the tarsal gland. Their results revealed that there were dozens of different species of bacteria commonly inhabiting the tarsal gland, and that the types of bacteria present often differed among different animals. It’s these different populations of bacteria that ultimately provide each deer with its own unique scent. Therefore, the mechanism by which the tarsal scent is produced is somewhat similar to how human underarm odor is produced, although we don’t urinate in our underarms!

(As a side note, the types of bacteria on the tarsal included some well-known species that are potential human pathogens, such as Staph, Strep, Listeria, among others. So, be sure to wash your hands after handling a deer’s tarsal gland!)

In a recent study, we identified 103 volatile compounds emanating from the tarsal tuft of male deer. Of these, 12 occurred in greater concentrations on dominant animals than on subordinates. Many of the compounds that we found on the tarsal gland were not observed in fresh urine, which further verifies that bacteria are important in the conversion of urinary compounds into socially-important odors.

Can a fresh tarsal from a buck be useful in a hunting situation? Certainly, but be careful how you use it. By placing a tarsal in a scrape site, or using it as a drag, you may signal a challenge to another buck. If he thinks someone is trying to invade his ‘turf’, he may return to the scrape more often, or follow the scent trail of the drag. However, timing of use is critical. Use of a tarsal scent likely would be most effective during the 2 to 3 weeks preceding the peak of the rut when scraping activity is at a peak. In contrast, it may be less effective during the peak of the rut when most bucks will be tending does. A buck tending a doe will be less likely to investigate the scent of a possible unknown intruder. He may actually try to direct the doe to another area to avoid a confrontation and the possibility of losing his prize!

THE FACTS ABOUT CWD & DEER URINE

15 July 2015

The spread of Chronic Wasting Disease is a matter we take very seriously. Tink’s has been following recent events concerning CWD and have been for many years. We have ongoing communications with the facilities where our urine comes from, various wildlife agencies, and top experts on this subject matter. We care about protecting whitetail deer and want to do our part to prevent the spread of CWD.

We monitor our urine suppliers and their facilities to insure they are in continuous CWD monitoring programs approved by the National CWD Herd Certification Program under USDA-APHIS. No CWD has ever been found in any of our facilities.

The Science…

The risk of CWD being spread from our urine based hunting scent products is virtually zero.

The speculations you may have seen inferring risk of urine based scents spreading CWD are not well founded.

In all of our searching and communication with experts, only two published studies we know of suggest any possibility of a link between urine and CWD transmission. Both studies involved experimental and artificial/extreme protocols that are clearly not present during normal use of a urine based hunting scent.

For example, in one of the studies, urine from clinically sick CWD positive deer was concentrated (10 fold) and injected directly into the brains of mice that were genetically altered to be susceptible to CWD. In this study 1 out of 9 mice became infected. Obviously hunters are not going around injecting deer urine into deer brains with a hypodermic needle.

Based on the experimental conditions, results and other consideration, Nicholas J. Haley, DVM PhD, who happens to be the lead author on both of those studies, has advocated against banning the use urine based products because the risk is so low.

It is simply in the best interest of any urine collection facility to have healthy deer. This along with the virtual zero risk, you can be extremely confident that you are not spreading CWD by using urine based scents.

We care greatly about the deer and about the tradition of hunting. If we thought our hunting scent products could spread CWD, we would not offer them.