July 01, 2017The whitetail's keen sense of smell serves in finding food, detecting predators, social communication, reproductive behavior, and probably a good many other things we humans don't fully understand.
Deer employ their super sense of smell year-round in conjunction with glandular secretions and body odors -- referred to as chemical signals -- as their primary mode of communication. Communicative odors produced by whitetail bucks probably include secretions from skin glands, urine, and saliva. Feces also serve as a means of odor communication in some animals and might in whitetails, too, but this has not been documented.
Whitetails have seven types of skin glands 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, found on the legs, and the preputial gland on the buck's penis sheath.
Unlike visual signs and vocalizations, which serve only immediate, short-range purposes, chemical signals can be deposited on objects in the environment. They can also identify the maker, permit scent-matching of scent marks with individuals, and produce long-lasting messages that continue to work in the maker's absence.
Springtime scent-marking at scrapes is a good indication that some of the local bucks survived the previous hunting season and winter period. Kenny Darwin photo
During the breeding season, bucks produce highly visible signposts, in the form of antler rubs and ground scrapes. These are violent aggressive action: Bucks use their antlers to rub the bark from trees, to thrash brush, and to break overhead limbs while depositing scent, and they paw the ground like irate bulls.
Bucks also judiciously scent-mark overhead branches when carrying velvet covered antlers. However, most such marking is so subtle that it's easily overlooked.
More than 30 years ago, I learned that bucks could easily be induced to scent-mark overhead branches and scrape where I wanted. All that was necessary was to provide an overhead branch in the right place. Placing cameras at such sites, year round, proved to be quite revealing.
In 1988, I hung 100 limbs at likely scrape sites throughout Upper Michigan's square-mile Cusino deer enclosure and used them to study deer marking behavior. Interestingly, 60 percent of the limbs were scent-marked by deer before scraping started in early October.
When marking branches, most of which are about head-high, a buck "mouths" the branch tips, rubs them with his forehead, preorbital area, nose, antlers, and chin, while pausing periodically to sniff and lick the branches. It's as if the entire process involved some highly sophisticated signal code -- like a baseball coach signaling his batter.
Close inspection will reveal frequently rubbed twigs acquire an oily or greased appearance, and deer hairs can often be found adhered to the tips of frayed branches.
In Northern Michigan, where many whitetails vacate their summering grounds and migrate long distances to wintering areas, bucks intensively scent-mark overhead branches on their traditional summer range as soon as they return in spring. Sometimes they even complete the full scrape sequence by pawing the ground and urinating at the site.
In my Cusino enclosure studies, I used automatic cameras set at limbs I purposely positioned for study. I found that bucks scent-marked small home ranges -- generally less than 200 acres in size -- during May and June, the period of maximum antler growth. In late July, however, when antler growth was nearly completed and the antler cores began to mineralize, some of the bucks wandered into adjacent doe-occupied ranges where they also scent-marked overhead branches.
Ninety-four of my 100 test limbs were scent-marked by bucks; 60 percent were marked before active scraping started. But I detected no serious limb-tip mutilation until October, at which time bucks began to paw the ground beneath scent-marked limb tips. In all, 83 percent of the branches bucks scent-marked during summer developed into scrapes in autumn.
So, the intensity, manner, and distribution of scent-marking by bucks changed as the summer progressed. Even the secretions, messages, and audience might have changed one month to the next.
I believe that scent-marking in spring helps bucks reclaim their familiar summering grounds, much of which has been devoid of deer during the winter months. It also probably intimidates pregnant does, causing them to seek other areas for fawn-rearing.
Whitetail bucks seem to have the capacity to emit a wide array of chemical signals, which presumably convey equally diverse messages, in order to satisfy their social needs. When combined with different methods of presenting the odors, the chemical languages of whitetails must be immense.
Despite what you might read in the popular literature and contrary to claims, scientists still don't know precisely what chemicals bucks use in their scent-marking.
Until we more fully understand their social behavior, we will have difficulty determining how whitetails "talk" to each other via chemical language, which substances are used, and precisely what messages are conveyed.
Whatever its cause and function, springtime scent-marking at scrapes is a good indication that some of the local bucks survived the previous hunting season and winter period. Use of automatic cameras at these sites will help to identify the markers and readers -- and I'll wager you capture far more images of bucks than does.