Target Species: White-tailed Deer (Odocoileus virginianus)
Shortening days and cooling temperatures trigger a change in North America’s most familiar native mammal, the white-tailed deer. Bucks that are normally mild-mannered and tolerant of one another turn violent and aggressive. They stalk the brush fueled by lust and rage, their antlers hardened and sharp, and rising from their skull like a crown of blades. Battle ready, they have come to compete in an ancient breeding ritual – the culmination of a year spent eating, growing, and preparing – the rut. And they will fight, sometimes to the death, to carry on their bloodline.
Shedding of velvet is the first indication that the rut is approaching. The fuzzy tissue that has nourished the growing antlers for the previous 6 to 7 months begins to dry and the underlying bone hardens. The process must cause the bucks to itch something fierce, as they furiously thrash their antlers against any available vegetation to speed up the process. As the velvet is stripped from bone, it hangs from the antlers in a bloody mess until it is completely removed. Adorned in their impressive new armaments, the bucks spar. The matches are friendly, for the moment, and no real effort is made to harm one another. The camaraderie is soon to come to an end, however.
In the weeks after their velvet has been shed, bucks who spent the spring and summer lounging and feeding together begin to grow intolerant of one another’s presence, and isolate themselves in the brush. Around the same time, the does are becoming reproductively receptive, and communicate their impending estrus through pheromones in their urine. They advertise their fertility by moving through the brush and leaving their chemical signature on the landscape.
The white-tailed deer is the widest ranging ungulate in the western hemisphere. They can be found from central Canada to Peru. As one might imagine, having such an expansive range means that there is considerable variation in the species throughout its distribution. Those at the northern extent of their range are the largest bodied. Following Bergmann’s rule, they become gradually smaller moving south. Antler size, however, is highly variable and more closely linked to local genetics and available nutrition than driven by thermoregulatory requirements.
The deer of the South Texas brush country are world famous for their impressive headgear. The larger than average antlers of a mature buck have been attributed to a number of factors, including the protein rich bounty of prickly pear, mesquite beans, and other foods found here. South Texas is also known for its heavily managed deer ranches, where selective harvest enhances genetics and supplemental feed bolsters nutrition.
During our Thanksgiving break this year, Carolina and I opted to visit south Texas in lieu of risking exposing ourselves and my parents to COVID by spending the holiday with family. We were able to enjoy a socially distant vacation on the beach and in the thornscrub. In the heart of the brush country we found an area with wild, free-ranging deer that found refuge in a large nature preserve where there was no hunting pressure and the animals were accustomed to human presence. This allowed us to observe the rut up close, and witness and photograph behaviors that would be nearly impossible to experience otherwise. I spent one evening and one glorious morning here, and walked away with images and memories of a lifetime.
As the rut nears, the necks of mature bucks begin to swell. Fueled by testosterone, they pack on muscle in preparation of the combat soon to come. The bucks also become bolder. As they move about their territories in search of receptive does, they become more active during the day, and are thus easier to observe and less prone to flight. They truly have one thing on their mind.
As the bucks move through their home range, they leave an abundance of sign. They will frequently visit antler height branches and take small twigs in their mouth. It may appear as if they’re feeding, but they’re not actually eating the twigs. Instead they lick them, and rub them against special glands on their face known as pre-orbitals that leave pheromones for other deer to detect.
Commonly known as “licking branches”, it is believed that they are used to communicate important information in the white-tailed deer community, including the status of a buck among the herd. Bucks visiting the licking branch can quickly ascertain what other bucks are in the area, and therefore evaluate threats to their ability to defend and breed a doe. Does too will use the licking branch, likely to determine which bucks may be nearby, and advertise when they are approaching estrus, that brief window when they are fertile.
As the testosterone fuels bucks with lust and rage, they seek outlets for their increasingly violent tendencies, and begin to thrash about vegetation including low hanging branches and tree trunks. Beyond serving as an outlet for their anger, these rubs, like the licking branches, serve an important purpose during the rut. The height of a rub and the destruction it caused can communicate the size and strength of a buck to would be competitors. It is also believed that bucks secrete additional pheromones as they rub, and that the act of seeing a mature buck thrash the hell out of a tree or small shrub serves as an intimidating warning to younger bucks that might witness it. After depositing his scent on a licking tree or creating a rub, a buck will typically dig a “scrape” by hoofing at the dirt and urinating over the metatarsal gland on his hindleg, further leaving his mark across the landscape.
As the does near estrus, the bucks really begin to take notice. Chemicals in a doe’s urine contain information as to her current stage in the reproductive cycle. It is the goal of every buck to breed as many does as he can during the rut, so this information becomes important when determining which lovely lady he should pursue. An experienced buck will focus on those does that are very near estrus so that he can minimize the time needed to guard and breed her before he seeks out another partner.
Bucks determine which does are approaching estrus through a process known as lip curling, or flehming. The strange crinkly-nosed face that they make during this process is known as the flehmen response. When a buck detects the scent of a doe’s urine, he will curl his upper lip back and pass the pheromone laden aroma through the vomeronasal organ in the roof of his mouth.
It is typical for a flehming buck to cock his head back forty-five degrees or so. Perhaps this maximized the efficiency of the organ’s ability to analyze the pheromones. It’s not uncommon to see a buck move his head up and down and from side to side at this time, as if trying to find the sweet spot for extracting doe pheromones from the air above her spoor. The response may last several seconds.
If all goes well with the Flehmen response, a buck will be able to determine which does are nearly ready to breed. If he detects the pheromones of “the one”, he will seek her out. The plan is to find her and tend her until she comes into estrus, during which time he intends to copulate with her as many times as possible to ensure conception.
A particularly receptive doe may entice a buck by initiating a game of cat and mouse, where she runs seductively to and fro in an attempt to illicit a chase response. More often than not, however, it is the buck that will pursue the doe, advancing toward her with his head lowered communicating his clear intention to mate. Does that are not yet receptive or unimpressed with their suitor will spurn his advances. A buck guarding a doe will make several of these “buck runs” until he receives indication from the doe that she is ready to breed.
In a perfect world, there would be plenty of does for all, and every buck would have equal opportunities to pass on their genes. That’s not the way things work, however, and competition for breeding rights is fierce. It is in a doe’s best interest to be choosy when it comes to a suitor so that she may ensure that her offspring have the best genetic blueprint for survival and success in life. It is also in the buck’s nature to try and breed as many does as he can, maximizing the continuation of his bloodline. When the stakes are this high, conflict is bound to arise.
I was incredibly fortunate to witness this firsthand in the South Texas brush. I spotted two bucks squaring off at the edge of a mesquite thicket. A young buck with an impressive set of antlers and an older buck with a smaller rack but noticeably larger body size were standing face to face. Both were posturing with their ears pinned back, communicating that neither intended to back down. I could feel the tension in the air and I readied my camera in preparation for what might ensue. Then, all of a sudden, the young buck rose onto his hind legs, dropped his head forward baring his antlers, and lunged forward at his opponent.
CRACK!! The bucks locked antlers with a clash that echoed through the brush. In an instant, both bucks disappeared into the thicket. I feared that this battle would occur in the dense vegetation, and dismayed that I would not bear witness to it. But then, in an instant, I saw the back of the young buck come flying through a brush pile, sending sticks splintering and flying in every direction, his antlers entwined with the old buck.
The old buck than wrenched his swollen neck muscles earthward, and slammed the young buck to the ground, pinning him there. In that moment I was convinced I was watching the young buck’s life come to an untimely end. The old buck was quite literally trying to gore him to death, thrusting repeatedly at his neck and withers. These contests may be intended to settle disputes of dominance and the right to breed, but for the bucks involved it is a matter of life and death.
But the young buck still had some fight left in him. With an incredible display of strength, he righted himself, sending dust and bits of grass flying through the air as he dug in his hooves and lunged forward once more in hopes of turning the tide of the battle. For a moment the two warriors jockeyed for position.
Strength and experience were on the old buck’s side, and he used his bulk and considerable power to push the young buck back. Eyes wide with fury, the young buck refused to quit and continued to push back against his opponent. It was incredible to witness the toughness and determination of these incredible animals. These were not the docile, familiar creatures that so many see when they look at the whitetail. These were warriors in the truest sense of the word.
Again the old buck wrenched his neck downward, this time bringing the young buck to submission. Knowing his defeat was imminent, the young buck now had to find a way to escape the fray with his life. Carefully and deliberately, the young buck broke free and beat a hasty retreat through the brush. The old buck momentarily gave chase, but satisfied with his victory he soon broke off his pursuit.
The young buck learned a valuable lesson that day, one that he will carry with him through future ruts. He clearly had all the makings for a future champion. One day he will be a true king of the brush country, and his days of losing fights will be behind him. I hope I have the opportunity to see and photograph him again.
It’s not just the big bucks that are driven to breed during the rut. The drive to procreate is strong, and younger and smaller bucks are not spared the lust. Their path to procreation may be more difficult, but the dominant bucks can’t be everywhere at once, and when they are busy guarding a doe or fending off incoming suitors, these “satellite” bucks are often able to sneak in and mate with some of the does in their territory.
Of course, what was presented here is just a small snippet of all that occurs during the rut. It is an event that lasts for a month or more, with a peak activity period of around 10 days, usually in November to the north and December further south. On average, a female is only in estrus for 24 hours or so, providing a limited window where fertilization can occur. Those does that are not bred during the first cycle will come into estrus a few weeks later. This, combined with a few does that come into heat early, prolongs the rut, but anyway you slice it, it is but a small, albeit supremely important portion of a deer’s annual cycle.
I still have a hard time believing my luck those days among the whitetails of the brush country. To witness a wealth of fascinating behaviors in such a short window of time was truly one of the most incredible experiences of my life. The white-tailed deer is perhaps the most famous, revered, and sought after animal in North America. It is so popular, common, and widespread that it oftentimes fades into the background for naturalists and wildlife photographers. But I can attest that those who put in the time and effort to try and learn their ways and experience their world will be greatly rewarded. From the hardwood forests of the east to the riparian woodlands of the west and the thornscrub of South Texas, may the white-tail deer continue to dig scrapes, lock antlers, continue their bloodlines, and capture the hearts of millions for many years to come.