Most hunters agree that a whitetail’s most-important sense is that of smell. Deer rely on their noses to locate food, detect predators, and communicate with other deer. Simply through the sense of smell, deer can recognize other deer, determine sex, dominance, and reproductive status. Because humans perceive the world primarily through visual means, it is difficult for us to fathom the importance of odors to whitetails.
One of the best ways to get an idea of how deer communicate with scents is to examine their different glandular areas. To date, seven glands or glandular areas have been identified on whitetails. Let’s examine them and what we know, or think we know, about each.
The interdigital glands are located between the digits (toes) on all four feet. Each gland is a small sparsely-haired sac containing a yellowish, cheesy material. The material often has a foul, rancid odor. Some of this scent is left in a deer’s track each time it takes a step. Several years ago, researchers at the University of Georgia (UGA) identified several compounds associated with this gland.
Interestingly, these compounds have different volatilities (evaporate at different rates) causing the odor of the track to change over time. This may be how a deer (or a predator) can determine the age of the track and direction the deer is headed. More recently, UGA researchers identified 46 compounds from the interdigital gland. Five of these occurred in much greater concentrations in dominant bucks than in subordinate bucks. What this means is unknown, but it is possible that pawing at scrape sites leaves a scent specific to dominant bucks.
The metatarsal glands are located on the outside of the deer’s hind legs. Each gland consists of an oval ring of whitish hairs surrounding a black callous area. The area beneath the hairs has large numbers of enlarged glands. While the function of this gland in whitetails remains unclear, in mule and black-tailed deer it produces an alarm pheromone (scent) that can alert other deer. It is possible this gland once served this purpose in whitetails, but is slowly losing its functionality. This has already occurred in some subspecies of whitetails, such as those in South and Central America, which completely lack this gland.
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The most-important glands to whitetails, the tarsal glands, are located on the inside of their hind legs. These glands consist of a tuft of elongated hairs beneath which is an area of enlarged glands that secrete a fatty substance, called a lipid, which adheres to the long hairs. All hunters who have harvested a buck know about the strong smell often associated with this gland. However, few realize that this smell does not come from the gland itself but rather from urine deposited on the gland. All deer— bucks, does and even fawns—urinate onto this gland in a behavior called rub-urination. Even fawns less than a month old urinate onto this gland at least once a day. Most of the time the excess urine is licked off the gland.
However, during the breeding season, bucks, especially mature bucks, urinate onto the tarsal much more frequently. They also stop licking off the excess urine. This frequent rub-urination, along with chemical and bacterial changes, is what stains the gland and gives the buck its rutting odor—thought to be unique to each buck like body odor is in humans. A deer’s unique tarsal odor is likely how one deer recognizes another. It also is used to determine their sex, dominance status and reproductive condition. Does likely identify their fawns through the tarsal odors.
Because the tarsal is so important in deer communication, it can also be used to the hunter’s advantage. By placing a tarsal from a mature buck into the scrape of another buck, you may signal a challenge to the buck. If he thinks someone is trying to invade his “turf,” he may return to the scrape more often. Using a tarsal while rattling also has its obvious advantages, as does making a drag from a tarsal gland.
The preorbital glands are small pockets located in front of the deer’s eyes. At most times, the pockets are closed. However, in certain situations, deer will flare open this gland. Rutting bucks may open this gland when signaling their aggressive intents to other bucks, while does often open this gland when tending their fawns.
Researchers remain uncertain whether this gland actually produces a scent. The opening of the gland may just be a visual display. Many hunters believe the preorbital is used to mark the overhanging branch at a scrape site. This may be true, but a buck typically marks an overhanging branch with his whole head— forehead, antlers, nose, mouth and preorbital area. Therefore, it is more likely he is leaving scent on the branch from several areas rather than just the preorbital gland.
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Nasal glands are two almond-shaped glands that empty into the nostril by a short duct. We don’t know if this gland produces a scent or just lubricates the nose. It is possibly used to mark overhanging branches in addition to other glandular regions of the head.
The entire area between the antlers and the eyes is another very important gland to whitetails. The skin in this area contains large numbers of apocrine, or sweat glands. These glands become more active during the rutting season in all deer, but especially so in dominant, mature bucks. It appears this gland is the source of scent left on antler rubs, and possibly on overhanging branches at scrapes. If you watch a buck making a rub, you’ll notice that he uses the bases of his antlers and his forehead region. He will often pause and sniff or lick the rub, apparently checking the scent he is depositing. Interestingly, we have observed does rubbing their foreheads on antler rubs made by bucks. The importance of this behavior is unknown.
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UGA researchers recently discovered another previously unknown glandular area on whitetails—the preputial glands. These glands are associated with long hairs that extrude from the buck’s penile sheath. While its purpose remains unclear, the glands could be important in helping bucks obtain their characteristic rutting odor.
So far seven different glands or glandular areas have been identified in whitetails. How many more will be found? Who knows, but it is likely there will be more. While much remains to be learned, armed with the latest whitetail science we will keep chipping away in hopes of solving the complex and fascinating world of whitetail scent communication.