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.
While the mating season, or rut, for moose peaks between late September and early October, mating behavior can already be observed. It is widely known that male, or bull, moose often paw a pit in the ground, urinate in it and then stomp in it in order to splash their underside, slap the urine with their antlers to disperse it, and lay down in the pit and wallow in their urine, soaking their undersides and neck. Their pungent urine serves as an aphrodisiac for female, or cow, moose, which are attracted to the pheromones it contains. A cow will enter a wallow, aggressively displacing the bull at times and even drink his urine.
However, it’s not just bull moose urine that attracts the opposite sex. The urine of a cow in heat (defined as the two days of their estrous cycle when they will allow a bull to mount them) is equally as attractive to bulls. At this time of their reproductive cycle cows frequently will urinate in the water and along the shoreline of lakes and ponds (look closely at photo).
As the moose rutting season comes to a close, signs of their breeding behavior are fewer and not as fresh. The pictured moose wallow, or rutting pit, was most likely created by a bull moose as a means of spreading his pheromones to receptive cows (although cow moose have been known to make them). After scraping the ground, the bull then urinates in the depression and stamps in it to splash the urine on his antlers (“antler perfuming”) and/or lies down in it, soaking the under side of his body, including the dewlap, or bell, that dangles beneath his neck. Every soaked surface serves to advertise his presence to cows in the area. Often the sound that the bull makes splashing the urine attracts cows, who run toward the bull and, by head bobbing and attempting to drink the urine (the sipping sound is attractive to both cows and bulls), encourage him to urinate more. (Thanks to Alfred Balch for photo op.)
During their breeding season, or rut, bull moose display a number of behaviors that are not commonly seen any other time of year, and many of these behaviors leave obvious signs, including broken branches, scraped bark, wallows and tracks. Bulls roam their home ranges, thrashing their antlers back and forth against shrubbery and saplings while leaving their scent. The sound of their antlers beating against vegetation is thought to signal the bull’s dominance to other males, as well as serve to attract females. The pictured broken balsam fir sapling and its frayed bark are evidence of this behavior.