Understanding Deer Glands
The whitetail deer lives in a world dominated by scent. They use their keen sense of smell to find food, find love, avoid danger, and to find one another. Their olfactory senses are, without a doubt, the most key component to a deer’s survival. Yet, perhaps the most fascinating aspect of their olfactory system is how they emit, interpret and communicate with each other via scent, specifically their external glands. Whitetails communicate primarily through chemical emissions and deposits via their external glands. In attempt to better understand the whitetail; I feel every hunter should possess knowledge of the following deer glands: tarsal, interdigital, forehead, preorbital and salivary.
When most whitetail hunters think of the external glands on deer, they think of the tarsal gland and for good reason. The tarsal gland is the single most important gland whitetails use to communicate with one another. Located midway down the inside of the deer’s legs, this gland retains a surplus of information. Both bucks and does use their tarsal glands as a means to display their sex, age and dominance. The gland itself emits very little odor as the hairs on the outside of the gland are pressed tightly together, allowing little odor to permeate the air. Tarsal glands do produce pheromones. However, it is not until a deer urinates on their tarsal gland (also known as “rub-urination”), or becomes frightened or aggressive is the dominant scent released. Rub-urination is most common, and almost used exclusively by bucks during the rut because of their increased levels of testosterone. There is a simple rule to follow when examining the tarsal glands on a buck: the darker the gland, the more dominant the buck. Reason being, dominant bucks are completely maxed out on testosterone and rub-urinate more than subordinate bucks, essentially telling all other bucks who is boss. Conversely, should a less dominant buck cross paths with a more dominant buck, he will actually lick his tarsal gland to reduce how strong of an odor is emitted to reduce their dominance and avoid a confrontation.
The tarsal gland also serves as the primary communication device on the whitetail’s body. When a deer encounters an unfamiliar deer, the first thing it does is smell the other’s tarsal gland. Think of it as the whitetail’s version of shaking hands. When one deer smells another’s tarsal gland, they learn all they need to know about that specific deer. Sex, age, rank in social order as well as breeding status during the rut can all be learned from the whitetails tarsal gland. It is for this reason alone that most hunters have the most success using tarsal gland scent as an attractant scent during the hunting season. Deer are curious creatures and when they encounter an unknown odor, they want to investigate, especially when it smells of the tarsal gland. During the deer hunting season, a hunter rubbed a tarsal gland gel on some trees and other vegetation and put a trail camera out to monitor the results. Within two days, 5 different bucks, including a 130” 10 pointer all came to investigate.
The interdigital gland is the second most important gland to the whitetail deer. Unfortunately, many hunters are unaware of its purpose let alone its existence because of where the gland is located. The interdigital gland is located between the deer’s two center toes, or hooves, and is the scent deer use to “track” one another. Think of the classic rut scene you may have experienced this past fall; a mature doe jogs by your treestand, immediately followed by a buck on the exact same trail as the doe, his nose just inches off the ground. Most hunters know that the buck is trailing her scent, but how? It is wrongly believed that he is simply following her scent, possibly her estrous level. It is true that he could be trailing the doe based on her estrous level and scent, but it’s more likely he’s following the scent left by the waxy substance that seeps out of the interdigital gland. This scent is left wherever the deer walks. Deer instinctively recognize the importance of this gland, as they can often be found cleaning the bottom of their feet after walking through mud or clay, enabling more scent to ooze from the gland, thus leaving a better scent trail. This helps deer find one another more quickly and efficiently because they are able to pick up the exact trail of the deer they are looking for. If whitetails had to locate one another simply by emitted body odor, they would waste a lot more energy and burn a lot more calories in the process. The interdigital gland also doubles as a warning scent for some deer. When deer are alarmed and frightened yet can’t identify the source of danger, they stomp their foot repeatedly in attempt to get the source of danger to present itself. In doing so, the deer is depositing more scent on the ground to warn other deer of danger in the future. If there was danger in the area, it is wise of the whitetail to educate other members of the herd to possibility of existing danger in the area. While deer pay close attention to this warning scent, I have witnessed several deer sniff the ground where a deer had stomped just hours before, only to resume feeding casually. If deer ran every time they smelled this alarming scent, there would be deer running through the woods constantly.
While the interdigital gland is responsible for bucks tracking does during the rut, fawns may actually benefit the most from this gland. After a fawn is born, it will spend the next 10-14 days alone in hiding, as the mother avoids leaving scent around her new born which may attract predators. When the mother goes back to find her fawn, she returns to the general area, but the doe is unaware of the exact location of her fawn since the fawn is likely to have gotten up and changed hiding spots. By following the unique scent trail left exclusively by her fawn and its interdigital gland, the doe is able to track and find her fawn.
The forehead glands are likely the most understood of all the external glands. Hunters are able to see and interpret the actions and results of this gland in respect to its purpose. Used almost solely during the rut, the forehead glands are predominantly used by bucks when rubbing trees and saplings. First, using his antlers, the buck rubs off the outer layer of bark on a tree. He will then rub his forehead on the same area depositing his scent. Bucks prefer to rub trees with aromatic bark, such as white or red cedars, several species of pine or sassafras. This is likely because the odor of the bark intensifies the odor left by the forehead glands or lengthens the life of the deposited forehead gland scent. Nevertheless, rubs are one of the primary sources of communication in the whitetail world. While it is the bucks who deposit this scent, the information within the scent is interpreted by both bucks and does. Bucks obviously deposit this scent as a means of establishing dominance and setting up territorial boundaries. Does, on the other hand, smell and sometimes lick the rubs where the scent has been deposited in attempt to find a dominant mate when she comes into heat. Similar to the color of tarsal glands, the same rule applies to the forehead glands. The darker the forehead on a buck, the more dominant the buck; dominant bucks are the creator of the majority of the rubs you see in the woods. As dominant bucks make more and more rubs, the forehead glands become more active, thus the secretions from this gland stain and darken the hairs on the bucks forehead. This is helpful information when trying to determine the age of a buck. Suppose you capture a picture of a buck on your trail camera that sports an impressive rack, however, his forehead glands are not stained dark. That is likely an immature deer with superior genetics and it may be wise to let that buck grow one more year. If its got a dark head of hair, it's a mature buck, so let him have it.
Preorbital and Salivary Glands
The preorbital glands, also known as the tear ducts are positioned on the front rim of the eyes. Many whitetail enthusiasts believe that this gland serves no real purpose to the deer, but some strongly feel otherwise. While the preorbital gland serves little purpose in the form of scent emission, it serves as more of a pleasure sensory to deer. While bucks rub their forehead gland on an overhanging licking branch while making or working a scrape, they also rub their preorbital glands. Bucks that do this seem relaxed and calm, similar to when humans get their back scratched. Again, it’s simply creates a pleasurable feeling for deer. It is possible, however, that deer do not use this gland very often because of its location to the eye and they fear the risk of injury.
While the purpose of the preorbital gland is subject for debate, the salivary glands serve a distinct purpose to whitetails. Whitetail saliva has a distinct ammonia based odor that the deer use for scent marking, similar to the forehead gland. When bucks utilize an overhanging branch at scrape, they bite the tip off the branch. They don’t bit the tip of the branch to eat it, rather because the roughened tip holds more saliva and thus more scent. That buck is essentially marking that scrape and the surrounding territory as his.
Whitetails use their external glands for a multitude of reasons; however, each one has its time and place. Whether it is to establish dominance, signal breeding status, or simple pleasure, deer rely heavily on their glands to communicate with one another. To observe and understand the purpose and use of all the glands in action, simply visualize a buck making and working over a scrape. First, as he paws out the ground, the scent from his interdigital gland is directly deposited on the ground. Next, he is likely to rub-urinate on his tarsal glands, or into the scrape itself. Then he will bite the tip off the overhanging branch, depositing his salivary scent on the licking branch. He will leave his forehead scent on the overhanging branch, and finally rub his preorbital gland on the branch simply for pleasure. In just one common whitetail action, taking less than 5 minutes, the buck employed the 5 major external glands while providing a surplus of information to other deer.
The whitetail deer is a fascinating, complex animal that many hunters, biologists and dedicated researches may never fully understand. However, I feel that breaking down the animal anatomically and physiologically gives a better appreciation of the whitetail. While learning the importance and usage of external glands on the whitetail may seem dull to some, I believe it gives valuable insight which will help us become a better overall hunter, but more importantly better understand the whitetail deer as a whole.