Buck Rubs: Bright Beacons Of Scent Communication and Visual Signals
As fall unfolds and the breeding season approaches for White-tailed Deer, testosterone increases in bucks, triggering the drying and shedding of velvet from their antlers. Bucks rub their antlers against shrubs and trees in order to remove the dried velvet, a process which is normally completed within 24 hours. Generally small-trunked, smooth-barked trees and shrubs ½ to 4 inches in diameter and without lower branches are preferred (Staghorn Sumac is often chosen, as depicted). Research shows on healthy habitat, rub densities can vary from a few hundred to nearly 4,000 rubs per square mile.
Rubs are far more than just a velvet-removal site, however. They serve as billboards posted for deer of both genders. Through specialized forehead skin glands, a buck deposits pheromones that convey social status, suppress the sex drives of younger bucks and stimulate does. Aggressive rubbing as well as increased testosterone strengthen neck and shoulder muscles, equipping them for battle with another buck should it vie for the same doe.
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White-tailed Deer Breeding Season Winding Down
The breeding season of White-tailed Deer extends from late October to mid-December. Fresh buck rubs, where bucks literally rub the velvet off of their antlers as well as communicate with other deer via their scent, can be found throughout this period of time.
Mature bucks make two distinct types of visual and olfactory signposts —early-season and breeding rubs. The early-season scraping of antlers builds up neck and shoulder muscles, designates a buck’s territory (both visually and by scent deposited from forehead glands) and releases aggression caused by rising testosterone levels. Later in the season, once the rut begins, bucks move out of their home ranges into doe territory, where they make breeding rubs. These rubs announce the bucks’ presence to does, and are thought to hormonally suppress small bucks to the point where their testosterone levels stay so low that they do not attempt to mate.
When a deer or moose strips bark off a tree to eat it, the de-barked area is torn only at one end — the deer grabs one end of the strip of bark and tears it off of the tree. The rubbing of an antler leaves ragged bits of bark at both the top and bottom of the rub. Staghorn Sumac, as pictured, is a favorite rubbing substrate.
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The Silent Communication of White-tailed Bucks
Rising levels of testosterone circulating in a buck’s blood toward the end of summer results in the maturation of antlers and the drying up of the velvet that was providing nutrients to them. It used to be thought that bucks engaged in rubbing their antlers against saplings at this time of year in order to remove the velvet, but research has shown there is much more behind this behavior. Rubs are visual and olfactory sign posts that transmit important information to other bucks and does in the area prior to and during rut, such as individual buck identification, breeding readiness, age and hierarchy.
The positioning of the antlers against a tree is not random — a buck generally rubs the base of his antlers and his forehead skin against the tree. The skin between antlers contains a multitude of scent-producing skin glands called apocrine glands (humans have them and utilize them during emotional sweating). These glands typically are inactive during the summer months, but in response to rising testosterone levels, they become increasingly active in the fall. The most active glands are found in mature dominant bucks.
Thanks to recent studies we know that more rubs are made in years of good acorn production than in poor mast years. Young bucks appear to make fewer rubs than mature bucks, and they tend to start rubbing much later in the fall (so rubs you find now were most likely made by mature bucks). Research suggests that older bucks may be making more than 1200 rubs during the roughly 90-day rubbing period, which comes to about 15 rubs per day.
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