Understanding a Buck's Personal Signature - the Tarsal Gland
Any deer hunter who has harvested a buck during the rut is familiar with the unmistakable odor emanating from his tarsal glands. While other glands play important roles in whitetail communication, none is more important than the tarsal. In many respects, this gland functions as a deer’s personal signature – its unique identification card.
Over the past two decades, numerous studies at the University of Georgia have greatly advanced our knowledge of whitetail communication. While many questions remain, let’s examine what we know, or at least think we know, about the role of the tarsal gland.
Understanding “THE” Whitetail Gland
Located on the inside of a deer’s hind legs, the tarsal gland consists of a tuft of elongated hairs which often are dark and highly stained, especially on bucks during the breeding season. The skin underneath this tuft has specialized muscles which allow the deer to flare the gland to release a burst of scent. Deer often flare this gland in response to physical trauma or during aggressive interactions with other deer.
Deer often sniff the tarsal glands of other deer, particularly those with which they are unfamiliar. The frequency of tarsal gland sniffing appears to be greater at night, probably because of reduced visibility. By smelling the tarsal scent, deer can not only identify the other deer, but they likely can determine its dominance status, sex, condition, and other socially important information. Aren’t you glad humans are a vision-oriented species!
Most hunters know that bucks urinate onto their tarsal glands during the breeding season during a process known as rub-urination, whereby a buck rubs both tarsal glands together while urinating. It is less widely known that this behavior occurs throughout the year (though less frequently). In fact, bucks and does will urinate onto their tarsal glands about once per day throughout the year. Even day-old fawns have been observed urinating on their tarsal glands. It is believed that does identify their fawns through unique tarsal gland odors. Interestingly, bucks will often smell and lick the tarsal glands of an estrous doe as a prelude to mounting. Clearly, the tarsal plays a critical role in many aspects of whitetail communication, reproduction and survival.
What Causes the “Rutting Odor?”
If you asked hunters what causes the distinctive “Eau de rutting buck”, most would say it’s a substance produced by the gland itself. The truth, however, is far more interesting and complex. Each hair on the tarsal gland is associated with a structure called a sebaceous gland that secretes a fatty material which coats the hairs. The hairs themselves contain scales to provide greater surface area for holding the fatty material. However, it’s not this material itself that gives the gland its strong musky odor. Rather, the smell comes from urine deposited on the tarsal gland during rub-urination.
However, any observant hunter has noticed that the tarsal gland smells nothing like the smell of fresh urine. So where does this stink come from? The warm, moist, nutrient-rich tarsal glands provide a perfect environment for the growth of numerous species of bacteria. As the urine runs over the tarsal hairs, the fatty material on the hairs selects out some of the fat-soluble 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. Retaining the odor requires daily ‘recharging’ of the gland with urine. So, the tarsal gland functions more like a scent wick than an actual scent-producing gland.
Since bucks urinate on their tarsal glands more frequently during the breeding season, it was originally believed that the fat-secreting structures associated with the hairs would become more active during this time as well. Instead, research has confirmed that the activity of these glands does not change during the year, and that there is no difference in activity between males and females. These results indicate that it is not a change in gland activity that causes a change in the smell of the tarsal gland. Instead, the change in smell (and color) comes from a change in the frequency of rub-urination, and perhaps from a change in some components of the deer’s urine.
Research has identified more than 100 unique compounds associated with the tarsal tuft on male deer. Of these, 12 occurred in greater concentrations on dominant animals than on subordinates. Many of these were not observed in fresh urine, which emphasizes the role of bacteria in converting urinary compounds into socially-important odors.
In addition to these compounds, there also are several dozen species of bacteria which commonly inhabit the tarsal gland. Importantly, the species of bacteria often differ among individual deer. It’s these different bacterial populations that ultimately provide each deer with its own unique scent, a process similar to how human underarm odor is produced. It is important to note that the types of bacteria on the tarsal include some potential human pathogens, such as Staphylococcus, Streptococcus and Listeria, among others. So, be sure to wash your hands after handling a deer’s tarsal gland!
Tarsal Glands for Hunting?
Given what we know about this fascinating gland, can a fresh tarsal gland from a buck be a useful hunting tool? Absolutely – especially if used in the appropriate context and at the correct time. By placing a tarsal above or in a scrape site, or using it as a drag, you may signal a challenge to bucks in the area. If one buck thinks another buck is trying to invade his ‘turf’, he may return to the scrape more often, or follow the scent trail of the drag.
Timing of tarsal gland use also is critical. Tarsal scent is generally most effective during the 2 to 3 weeks prior to the peak of the rut when scraping activity is highest. In contrast, it likely would be less effective during the peak of the rut when most bucks are tending does. A buck tending a doe is less likely to investigate the scent of an unknown intruder. In fact, he may actually direct the doe to another area to avoid a confrontation and the possibility of losing his prize!
If you don’t have access to fresh tarsal glands, several companies now sell tarsal glands, or at least tarsal scent collected from rutting bucks. So, armed with this latest Whitetail Science, you may want to consider incorporating the use of tarsal glands (or tarsal scent) into your hunting approach this fall.
Brian Murphy is a wildlife biologist and CEO of the Quality Deer Management Association (www.QDMA.com). He also has been an avid bowhunter for the past 30 years. Dr. Karl V. Miller is a professor of wildlife biology at the University of Georgia and among North America’s leading researchers and authorities on white-tailed deer.