By Bob Humphrey
Scent is the principal means of communication for whitetails. They have at least seven glands or glandular areas that secrete different odorous compounds, all of which convey a remarkable amount and variety of information. They also have a nose rife with sensitive scent receptors that together represent a scent-detection system far superior to our own. We’re still just scratching the surface, but we are beginning to gain a better understanding of the type of information being communicated.
You’ve Got Mail
It would be a stretch to suggest deer intentionally use scent to convey specific messages, such as, “I’m ready to breed, or to fight, depending on who comes along next,” although that’s probably pretty close to the message that gets sent. They do take deliberate action to transmit scent messages, but they don’t really comprehend why. It’s just programmed into their DNA.
We’ll use the example of a buck tending a scrape. Whether it’s a dominant buck making a scrape, or a subordinate buck, or even a doe merely visiting the scrape, they all follow something of a routine. The first action is usually to sniff the branch. In computer terms, the deer are checking their inboxes to see who has left messages. If you watch carefully, you might even see them lick their nose, which enhances olfaction. Next, they may do one or a combination of things.
Just in front of the eye is an opening to the pre-orbital gland. Deer often delicately work twig ends into these pores, depositing scent from this gland. On numerous occasions, I’ve observed deer do this not just on licking branches, but seemingly on random twigs as well.
Clearly, more research is needed here to see if these other branches have any significance. Are they really random, or do deer use the same non-licking branches? If so, what message is being conveyed? Regardless, the message to hunters is that you need to be careful about leaving human scent on any vegetation in the areas you hunt.
On a deer’s forehead are large numbers of “tubular apocrine sudoriferous” (scent) glands. Research shows that, during the rut, glandular activity here is moderate in females but very high in males, consistent with the annual testosterone cycle. Furthermore, activity is highest in dominant males and lowest in fawns. Therefore, it isn’t surprising that forehead rubbing by males increases during the rut. And as you well know, licking branches aren’t the only things they rub.
I’m old enough to recall a time when conventional wisdom said that bucks rub trees to rid themselves of velvet, period. Thanks to research, and several million hours of anecdotal observation by hunters, we now know rubs also serve as visual and olfactory signposts, and that the forehead is a “scent organ” bucks use to anoint these rubs during the rut. We still don’t know exactly what information is being passed on, but we can speculate that bucks may be communicating identity, health and dominance/breeding status.
Furthermore, local deer have probably learned these are good places to catch up on the local gossip. Scrapes and rubs are essentially the message boards and chat rooms of the whitetail world. It’s no wonder, then, that they can be productive places to hunt.
While the interdigital gland may be the most underrated, internal glands that secrete compounds into the urine may well be the most important for scent communication, at least during the rut. Consider how much information a medical lab can discern from a simple urine test. Now, consider again how sophisticated and keen a deer’s sense of smell is. With a single whiff, they could be conducting their own urine test.
Let’s go back to our scrape, where we observe that, in addition to working the licking branch with pre-orbital and forehead glands, a buck also rub-urinates. The rubbing component involves the tarsal glands; located on the inner hocks, they release a waxy material consisting of sloughed skin cells and volatile fatty acids. As with the forehead, glandular activity increases during the rut, and the coarse hairs covering these glands become darkly stained. While rubbing the hocks together, a buck also urinates on his hind legs, combining urine and glandular secretions to create a pheromone-laced solution. He’s communicating that he is ready, willing and quite able to breed.
It takes two to tango, and on the other side of the dance floor is our doe. When she is ready to breed, internal glands release pheromones into her urine. She may not even need to urinate to release them, but when she does, her “perfume” becomes a siren song for every buck within smelling distance. Most of you have observed what happens when a buck catches a whiff of this seductive tonic.
The good news: Scientists have identified and isolated the odor molecules that signal a doe’s readiness to breed. The bad news: They’re so volatile that they evaporate within minutes of exposure to the air. In order to advertise her reproductive state, a doe must continue to produce these pheromones, which she will do for several days. If not bred during her first estrus cycle, she will recycle roughly 28 days later.
Because the volatiles in urine evaporate so rapidly, urine-based deer lures probably don’t work as well as we might like. That doesn’t mean you should give up on them, though. They do work sometimes under the right circumstances, so they must still be conveying some type of positive message. It may merely be a suggestion that other deer have been in the area recently, or it could be something far more complex. At this point, we just don’t know. Maybe we never will.