Signpost Science: What Research Tells Us About Buck Rubs

White-tailed deer have an elaborate system of communicating in dense cover. Before and during the rut, they use rubs and scrapes to communicate dominance, identity, reproductive condition and other socially important information. Buck rubs serve a special role because they are long lasting. Even in the absence of the maker, rubs carry messages that have physiological and psychological effects on other deer — and hunters.

Why do bucks make rubs? Where do they make them? What messages do rubs convey? What tree species do bucks prefer to rub and why? Why do some bucks rub more than others? How many rubs does a buck make? Will a buck return to its rubs? Do different rubs serve different purposes? The list of questions seems endless.

You are reading: Signpost Science: What Research Tells Us About Buck Rubs

To answer these questions, let’s examine what researchers know, think they know and admittedly don’t know about buck rubs. Hunters who can interpret these signs add considerable self-satisfaction and greater success to their hunts. However, rules concerning rubs in one part of the country might not apply to another.

Defining the Signpost

Bucks naturally scar trees and shrubs while rubbing them to remove antler velvet, but velvet stripping is generally accomplished within 24 hours. Bucks also make rubs while sham fighting. Bucks rub as long as they carry hardened antlers, so most rubs are made for other reasons.

Buck rubs are visual and olfactory (chemical) signals. They are showy and are anointed with various glandular secretions. Bucks might even grunt while making rubs, thereby attracting the attention of other deer. Dominant bucks sometimes make signposts in the presence of other deer, especially before contesting dominance or after emerging as the victor in an aggressive encounter.

Investigations conducted by Thomas Atkeson and Larry Marchinton revealed whitetails possess specialized forehead skin glands that become especially active during autumn. Bucks and does have these glands, but mature, socially high-ranking bucks tend to excrete more from them. Because rubbing is done primarily with the antler base and forehead, each rub carries the maker’s identifying odor.

Rubs’ Social Role

According to noted deer researcher Karl Miller, pheromones found on rubs might include “releaser pheromones, which evoke an immediate behavioral response; priming pheromones, which result in a physiological response; and informer pheromones, which relay information, but generally do not result in a behavioral or physiological response.”

Miller proposes such signposting by dominant bucks plays a vital role in maintaining social harmony in whitetail populations. He suggests primer pheromones deposited by dominant bucks at rubs (and scrapes) help synchronize reproductive cycles, bring adult does into estrus early, and suppress the aggressiveness and sex drive of young bucks.

My own scientific studies support Miller’s hypothesis. For example, when my colleagues and I confined bucks and does together during autumn, mean breeding dates were eight to nine days earlier than normal. Whatever the precise mechanism, these observations suggested bucks had some type of bio-stimulating effect on does (which could have been caused by pheromones) that induced ovulation earlier than normal.

We also verified the social significance of buck rubs with automatic cameras. Mature bucks made most of the rubs, but adult does and young bucks were the primary visitors to authentic and mock rubs.

Studies conducted in Georgia with tame, free-ranging deer have also shown does are readily attracted to buck rubs. While following tame deer, researchers found adult does frequently paused and sniffed fresh buck rubs. The dominant doe, in particular, often licked or nibbled the rub, and sometimes even rubbed her forehead directly on the rub.

Work conducted by David Guynn and his co-workers at the Mount Holly Plantation in South Carolina also supports Miller’s hypothesis. When the plantation’s doe population was reduced and the buck age structure increased, the rut became earlier, shorter and more intense.

Some researchers even speculate the availability of trees for antler rubbing influences deer distribution. In South Dakota, for example, researcher Michael Oehler and his associates hypothesize, “The relatively recent advance of deer into previously unoccupied areas of the Great Plains may be partially related to an increased encroachment of trees in prairie environments, and their importance as signposts for deer.”

Other cervids also use rubs as a means of communication during the rut. Even cow moose mark trees at the peak of the rut when most cows are in estrus. Such behavior by females leads researchers to believe tree-marking communicates the presence of estrous cows to bull moose. Also, rubs made by bulls late in the rut might serve a similar function to urine-soaked rutting pits: attracting females that weren’t bred during peak rut.

Rubbing Pattern Variables

The seasonal rubbing pattern depends primarily on herd density, velvet-shedding dates and buck age structure. However, even without hunting mortality, a shift in deer activity from one habitat type to another might influence the seasonal rubbing pattern.

Mature, dominant bucks that maintain their status by intimidating rival bucks during summer mark their former breeding range soon after removing velvet — before contesting dominance with other bucks.

Yearling bucks are delayed, physiologically and psychologically, in entering rut. Even the most physically fit yearlings are generally delayed a week or two in shedding velvet and don’t achieve the sex hormone “highs” that stimulate mature bucks. Because yearlings and 2½-year-olds normally make few rubs during the pre-rut, abundant rubs during September and early October invariably reveal the presence of a dominant buck at least 3½ years old.

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Although some studies suggest rubbing activity peaks before the breeding season, other studies indicate rubbing activity remains relatively constant from mid-September to mid-December. Rubbing intensity generally decreases sharply after the rut, but bucks continue making rubs as long as they carry antlers. Dominant bucks might rub tree stems after casting their antlers, but these rubs are subtle and difficult to locate.

Rub Distribution

Marchinton and Terry Kile were among the first to investigate the distribution of rubs and scrapes. In Georgia, they concluded rubs and scrapes were not randomly distributed. Although rubs and scrapes were sometimes made close together, statistical analysis revealed they tended to be clumped independently of each other. Rubs were concentrated in areas with many small saplings, whereas scrapes usually occurred where the understory was relatively open.

David Nielson and his co-workers confirmed much of the Georgia findings with their work on an Ohio tree farm. The Ohio investigation revealed the clumping nature of buck rubs might be related more to location and size of preferred tree and shrub species than to other factors. Under plantation conditions, bucks commonly struck several small trees in a row, or neighboring row, in a single rubbing episode, which led to rub clumping. Also, non-preferred trees such as hawthorn were sometimes rubbed if they were adjacent to preferred species. But bucks seldom rubbed hawthorns when growing with other hawthorns in a block.

During my work at Michigan’s famed Cusino deer research enclosure, where deer were supplementally fed and in superb physical condition, I documented bucks normally carried their antlers well past the breeding season. During winter, bucks heavily rubbed trees near favored bedding sites and along heavily used trails from bedding to feeding sites.

Buck-Rub Densities

In northern Georgia, Miller and his co-workers found bucks rubbed 47 of 58 tree species present. Preferred species for rubbing included alders, cherries, Virginia pine, Eastern juniper, white pine, striped maple and common witch hazel. Bucks avoided species with low branches or warty bark. Miller and his crew recorded rub densities from 474 to 1,502 rubs per square mile. Rub density was closely related to the number of bucks older than 2½ years in the population.

In the latter study, rub density and distribution changed from year to year, depending on acorn abundance. Acorns served as an important food source for deer in the area. Researchers recorded more rubs during years of good acorn production, when rubs were also more concentrated in oak habitat. Because rubbing activity varied according to food abundance and buck age, researchers concluded rub counts would not be a useful index to buck abundance.

Miller and Marchinton reported even higher rub densities (3,686 rubs per square mile) in a second study conducted in northern Georgia where deer densities approached 100 deer per square mile of deer range. They attributed this high rubbing rate to the presence of more than three mature bucks per square mile.

Usually, rub densities are higher in habitats with abundant food sources. Prime rub locations included wooded cover near corn or alfalfa fields, oak habitat when acorns are abundant, areas adjacent to forest openings where deer find lush herbaceous growth, and locations near artificial feeders or areas near any type of concentrated food source. Hence, rub concentrations might shift in accordance with changes in the distribution of preferred foods.

Bucks also concentrate rubs at trail junctions and along old roadbeds. In mountainous terrain, rubs might be concentrated along travel corridors, such as deer trails, ridgetops, stream junctions and old logging roads.

Species Preferences

A mature buck in rut, deprived of favorable tree stems for rubbing, will rub just about any type and size of tree — even fence posts and utility poles. However, scientific literature indicates bucks prefer to rub small-diameter, smooth-barked trees and shrubs. Preferred species differ by region, depending on what’s available.

In southern Georgia, Marchinton and Gerald Moore found bucks rubbed Eastern red cedar, winged sumac, sourwood, sassafras, short-leaf pine and long-leaf pine most often. Bucks selected stems from ½-inch to 4 inches in diameter, with the average about 1 inch in diameter.

In northern Georgia, where deer density was high, Miller and Marchinton reported bucks rubbed 32 species of trees and shrubs. Bucks preferred sumac, hazel alder, loblolly pine and Eastern red cedar. Bucks avoided privet, sweetgum and white oak. Most bucks rubbed in hardwood forests, clear-cuts and edges. Few rubbed in pine/softwood habitats.

Subsequent work by Kile and Marchinton showed bucks prefer to rub trees and shrubs with smooth bark and no lower limbs. They also found aromatic tree species, such as black cherry and sweet gum, were rubbed more frequently than expected. As a result, they suggested the aromatic qualities of a rubbed tree increase the rub’s effectiveness as a visual and olfactory signpost.

In South Dakota, Oehler and his co-workers also found bucks selected aromatic species for signposting and avoided species with thorns. They observed bucks rubbed eight species, including juneberry and chokeberry. Bucks avoided green ash, fleshy hawthorn, box elder and wild plum. Although trees averaged only about ¾-inch in diameter, bucks selected larger trees, averaging about 1 inch in diameter.

Merlin Benner and Terry Bowyer observed somewhat different results in Maine. These researchers found abundant rubs along forested edges of open fields. Bucks rubbed 12 species of trees and shrubs, including willows, staghorn sumac and trembling aspen, while avoiding chokeberry, black cherry, paper birch and sugar maple.

Interestingly, bucks in Maine and Georgia rubbed sumacs. However, Georgia whitetails preferred to rub cherry trees, but Maine deer avoided them. Likewise, bucks frequently rubbed sweetgum in central Georgia, but avoided it in northern Georgia.

My Upper Michigan studies closely match the Maine studies. The most attractive buck rubs in Michigan were located along forest opening edges, where deer can detect them from a distance. Bucks might rub just about any 2-inch diameter tree at these sites. However, given a choice, bucks selected smooth-barked trembling aspen most often. Aspen is easily debarked and the light-colored inner wood exhibits long-lasting brilliance when rubbed. Although aspen produces a bright signpost, it is not aromatic.

Licking Sticks and Traditional Rubs

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Leonard Rue III and Grant Woods observed certain rubs might serve special purposes. Rue identified what he calls “licking sticks,” which are short, small-diameter, broken-off shrubs. Woods investigated “traditional rubs,” which are large-diameter trees rubbed in successive years.

Most licking sticks I’ve encountered have been broken-off shrubs about ¾-inch in diameter and from 2 to 3 feet tall. They’re usually located in open areas. Bucks apparently vigorously rub slender stems until they snap off. Rue reported several different bucks might visit, rub and lick the same stem. Licking sticks are used for one season.

In South Carolina, Woods found bucks rubbed some large trees year after year. He observed older bucks, in particular, selected certain larger trees to rub, and re-rubbed the same tree frequently. Bucks preferred making traditional rubs on highly aromatic sassafras trees larger than 3½ inches in diameter.

Woods hypothesized, “The aromatic qualities of sassafras must enhance its function as a source of olfactory communication by alerting deer in the area that a communication signpost is present. Once deer are alerted by the visual and aromatic qualities of a rubbed sassafras that a signpost is present, they can then approach the rub and receive or deliver an olfactory communication signal.”

Obviously, a traditional rub pole has certain attractive characteristics. Their aromatic property might be one of them. However, the most frequently used traditional rub I found in the Cusino enclosure was a utility pole that reeked of wood preservative and tar.

Rub Reuse

Some rubs are re-rubbed during the same season, and sometimes year after year, as in the case of traditional rubs. However, most rubs are not re-rubbed. Instead, bucks are more inclined to rub a nearby stem when they return to a site.

In the study by Kile and Marchinton, for example, bucks rubbed 193 different trees, but there was no evidence any tree was rubbed more than once during the one-year study. Even so, these researchers reported the proportion of high-visibility rubs increased from September until rubbing ceased in January. In other words, bucks put more effort into their rubbing as the season progressed.

The above results differ from those reported by Anton DeVos for bucks in Ontario. DeVos observed nine of 30 white spruce trees in a conifer plantation were rubbed during consecutive years. However, Scotch pine and white pine in the same plantation were not re-rubbed.

Studies using artificially positioned stems produced more puzzling results. In September 1993, I cut 25 2-inch diameter aspen saplings outside the Cusino enclosure. I then cut the tops off and trimmed all branches, leaving poles about 8 feet long. I stuck them in the ground along forest openings in the enclosure, and within five weeks, all were re-rubbed multiple times.

Similar results were found during follow-up studies using four different species — aspen, black cherry, balsam and sugar maple. Aspen showed the highest rubbing rate (100%) and the highest re-rubbing rate (96%). However, even sugar maple, the least desirable species for rubbing, was occasionally re-rubbed the same year.

Conclusion

Buck rubs are signposts. They are visibly attractive and carry the maker’s glandular secretions. Most are made by mature bucks as a show of dominance. Mature bucks are also inclined to rub earlier in the season, rub larger-diameter trees and re-rub trees more often than young bucks.

But what is more important, a showy or aromatic rub? Study findings are contradictory. Some researchers conclude deer select tree species that are aromatic for rubbing, while others indicate trees providing a highly visible signpost are more important.

Certainly, the purpose of any rub is to draw the attention of other deer. Species selected for rubbing might vary across the country, depending on vegetation density, type and location relative to deer activity.

Given the opportunity, bucks tend to select tree species that are smooth, easily de-barked, devoid of lower limbs and 1 to 4 inches in diameter. If the rubbed stem produces an attractive aroma, that’s a plus.

I’m convinced, however, that the most attractive stems for rubbing occur along opening edges, where they can be seen from considerable distances. In such cases, a highly visible blaze is most important — whether the species is aromatic makes little difference. However, aromatic tree species might be more important for rubbing in dense cover.

— John Ozoga has been D&DH’s top research contributor for more than 20 years. He is a retired deer research biologist.

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