November 01, 2017Even we humans can relate to, and differentiate, the intents involved in affectionate facial grooming versus that of a nasty, swift kick. And although whitetails are not overly vocal, they will sometimes emit subtle bleats, mews, grunts, snorts and wheezing sounds to accompany and enhance the effectiveness of a given bit of body sign-language.
With a forest-dwelling animal like the whitetail, however, glandular secretions and scent-marking, referred to as chemical signals, tend to play an even more important role in communication than do visual signals and vocalizations, since the latter serve only immediate, short-range purposes. Nonetheless, despite the powerful role that odors play in the lives of whitetails, even the most astute observer will have great difficulty discerning the chemical signals deer exchange when they interact.
When compared to animals, it has been said, we humans have no nose. We humans can't detect odors as well as deer, nor can we think like deer. But, we are beginning to understand more fully the mechanisms, functions, and significance of odor communication among whitetails. Findings from Georgia-based research, in particular, indicate that the whitetail's world literally fumes with complex odor signals that play a very special, year-round role in the animals' social lives.
As far as we know, the communicative odors produced by deer may include secretions from certain skin glands, urine, vaginal secretions and, probably, saliva. Feces also serve as a means of odor communication in some mammals, and probably do in whitetails too, but this has not been documented.
Researchers have identified seven types of skin glands in white-tailed deer that likely play some role in scent communication: The forehead, preorbital and nasal glands located on the head, the tarsal, metatarsal and interdigital glands on the legs, and the preputial gland on the buck's penis sheath.
Researchers have identified seven types of skin glands in white-tailed deer that likely play some role in scent communication. These include the forehead, preorbital and nasal glands located on the head, the tarsal, metatarsal and interdigital glands on the legs, and the preputial gland on the buck's penis sheath.
To solve some of the communication problems associated with living in dense cover, white-tailed deer have evolved an elaborate system of scent communication by establishing "signposts," which they use effectively during the autumn period. These signposts are more popularly referred to as "buck rubs," made when bucks rub trees with their antlers, and pawed areas in the soil, referred to as "scrapes," which include urine deposits as well as scent-marking of overhead tree branches. These signs are primarily made by mature, dominant bucks throughout their range, before and during the autumn breeding period, presumably to communicate their dominance, individual identity, and other information of social importance.
Signposts arc both visual and olfactory signals in that they are showy in nature and are scent marked with various secretions. In some cases, bucks might even emit auditory signals while making signposts, thereby attracting the attention of other deer. Dominant bucks also sometimes make signposts in the presence of other deer, especially right after emerging as the victor in an aggressive encounter.
Unlike other forms of communication, signposts virtually serve as an extension of the animal itself, remaining functional for extended periods of time even in the maker's absence. Thus, signposts convey long-lasting messages that likely have both physiological and psychological impact upon other (generally subordinate) deer in the area.
According to Karl Miller, "Chemical signals that relay information among animals are called pheromones. This term was originally coined to describe chemical sex attractants in insects, but has since been expanded to include any chemical produced by one individual that transfers information to another member of the same species; some researchers reserve 'pheromones' for insects and use 'chemical signals' when referring to mammals.
"Whatever the terminology," notes Miller, "these signals include releaser pheromones, which evoke an immediate behavioral response; priming pheromones which result in a physiological response; and informer pheromones, which relate information but generally do not result in behavioral or physiological responses."
Miller proposes that signposting by dominant bucks plays a vital role in maintaining social harmony in white-tailed deer populations. He suggests that primer pheromones -- those which produce a physiological response -- deposited by dominant bucks at rubs and scrapes help synchronize reproductive cycles, bring adult does into estrus early, and suppress the aggressiveness and sex drives of young bucks. These are conditions which help maintain, and improve, the health and vitality of the population.
Studies conducted at the Cusino Wildlife Research Station in Michigan's Upper Peninsula lend support to the idea that the presence of mature whitetail bucks has a definite effect on the reproductive physiology of does. Despite the relatively narrow breeding window that prevails at the northern Michigan latitude, confining bucks and does together during autumn resulted in advancing mean breeding dates by eight to nine days. The exact mechanisms involved here were unknown, but observations suggested that the close and unnatural confinement of bucks with does had some type of biostimulating effect and could have been due to pheromones produced by males, which induced ovulation earlier than normal.
In whitetails, the adult sexes live apart much of the year, meaning that they may not associate for sufficient periods to allow priming pheromones from the male to alter the physiology of the female. Therefore, Miller suggests: "If continued exposure to chemical signals is required for biostimulation of female whitetails, as it is for domestic animals, rubs and scrapes probably serve this purpose."
Currently, most deer population management strategies in this country emphasize controlling total deer numbers relative to the perceived food and cover resources available. Little management concern is expressed maintaining populations of favorable sex and age composition -- deer populations that exist in social harmony. Exceptionally heavy harvesting of antlered deer, regardless of age, is generally encouraged by today's game management policy, sometimes contributing to grossly unbalanced adult sex ratios and leaving the physiologically and behaviorally immature yearling bucks to function as herd sires at an abnormally young age.
My research indicates that well-nourished yearling bucks can fulfill the role of herd sires, at least on northern range, by impregnating does on schedule with no decrease in the number of fetuses conceived. However, yearling bucks in my studies demonstrated a distinct lack of ritualized courtship behavior -- exhibiting instead what I'd call a "seek-and-chase" courtship because yearling bucks are delayed in sexual development and do minimal signposting, they likely lack the biostimulating effects demonstrated by mature bucks and necessary to synchronize estrus among does -- at least in southerly environments where photoperiod effects are not nearly so overpowering and whitetails have a long breeding season.
Most certainly, the inept courtship behavior employed by yearling bucks, and the lack of a firm dominance hierarchy in the absence of nature bucks, minimizes the chance for female mate selection. In the long run, this could reduce genetic fitness within populations wherever yearling bucks, solely, function as herd sires.
Only recently have wildlife biologists questioned how hunting-induced mortality (or lack thereof) influences deer social behavior. In turn, researchers are striving to better understand how such behaviors as signposting impact deer biology. In the process, they've learned that, while nutrition is of paramount importance in producing healthy productive whitetails, sociobiological factors also play an intricate role.
As a result, some biologists, especially those involved in promoting quality deer management, are now calling for revolutionary
changes in traditional deer-management practices by placing increased emphasis on the restructuring and maintenance of deer populations that have optimal social structure, in addition to being nutritionally balanced.