Though the sexual behavior of powerful men has been much in the news lately, an equally riveting drama of the sexes has been playing out in our own little forest. The White-tailed Deer rut (breeding season) is winding down, and considering the buck behaviors I’ve witnessed, I can imagine many of the does breathing a sigh of relief.
I’m a firm believer that even our weirdest human behaviors have a biological basis, and by learning about the behaviors of other animals we can see we’re not so different. However, the complex antics of the rut have been finely tuned by natural selection to one end only – the birth of healthy fawns the following spring.
So how do White-tails handle relations between the sexes? Most of the year by avoiding each other; this typical winter group of does and their offspring includes only young bucks with their families.
By next spring these young bucks will be chased off by their mother’s flailing hooves, a seemingly harsh behavior that protects the herd from inbreeding. For the rest of the summer and early fall the bucks will lay low; wandering widely and usually in small “bachelor” groups while they grow their antlers.
Does with young fawns will stay on their territory, along with their female offspring from the previous season. Deer society is a matriarchy; only does truly hold territory for the purpose of birthing and raising fawns. An older “matriarch” doe leads her family group most of the year, and may chase off bucks and unrelated does that intrude.
See this link for a very funny article about gender differences in Mule deer, which applies to White-tails as well. http://fwp.mt.gov/mtoutdoors/HTML/articles/2005/muledeer.htm
By early fall the convivial, laid-back bucks of summer are feeling more aggressive. Waning day length stimulates an ever-increasing production of testosterone, and mature bucks undergo an amazing change in physique. Antlers reach full growth and velvet is shed; hormones swell neck and chest muscles to an impressive bulk. Newly buff bucks, particularly dominant ones, seek out small trees to shove and rub with their foreheads. Often trees and shrubs with a strong fragrance are chosen, to enhance the odors from a buck’s forehead glands.
To understand deer society, imagine the tweet you send is made of scent instead of words. This olfactory news is composed of oodles of chemical compounds secreted in urine and from glands, enabling deer to share intimate details about themselves. During the rut, dominant bucks use scent marking to project their identity, status, health, and hormonal state for both does and other bucks to read. A single buck can make hundreds of rubs in one rut season; this really has an impact on our little forest, where young trees are already scarce. Rubbing is followed by “scraping”; bucks massage their forehead glands on a low hanging branch, then paw and antler rake a bare area below and urinate on it. Researchers believe these chemical message boards have a dual purpose – the same information may serve to intimidate younger bucks, while intriguing near-estrus does!
As does come into the estrous part of their cycle, their urine contains chemicals that inform bucks of their hormonal status. Scenting for does that will be receptive soon, bucks begin stalking and chasing the does that are “in heat”. This is the time that hunters really want to be out in the woods, since preoccupied bucks are much less wary.
Much of the info I read to research this post came from hunting websites, which would lead one to believe that the rut is mostly about the behaviors of big bucks. However dramatic the rubbing, scraping, sparring, stalking and chasing – all these activities are geared to one end only. They allow the fittest bucks to be as close as possible to estrous does during their brief 24 hour receptive period. The actual breeding activity of the rut lasts only a couple weeks; this concentrated frenzy ensures that fawns will be born at just the right time in spring.
Even so, dominant bucks can’t possibly do all the breeding. A buck and doe usually spend about 48 hours together before mating is completed. Most does in a an area come into estrus within days of each other, so smaller and younger bucks will find opportunities too. In fact, researchers have found multiple paternity in about 22% of twin White-tail fawns, proving that does may breed with more than one buck.
A doe’s urine contains chemicals that inform bucks of their hormonal status. With a buck stalking her, an estrous doe’s behavior is often somewhere between “come closer” and “leave me alone”. But there’s nothing coquettish about it – her hormonal state alone dictates when she is ready to breed, and she chooses which buck(s) she’ll breed with. Until then she will run at a buck’s close approach, and of course the buck follows, desperate not to lose her. High speed chases are a dramatic and visible feature of the rut; while I’m working in the forest it’s unnerving when a pair of oblivious, stressed-out deer suddenly races by!
Even older doe fawns may have a breeding cycle their first winter, if they’re well nourished. Though we’d consider this teen pregnancy, it allows deer populations to increase quickly after depletion by starvation or predators. The link explains why it’s an indicator of good health for a deer herd (though not a good sign for the health of our forest!) https://www.qdma.com/doe-fawns-breed-good-sign/
Another view of the large buck in the opening pic; he’s always looking in the same direction for a very good reason…
… his eye was on this young doe nearby, who was not running away, so maybe things were going well.
And of course the end result of all this is a lot more deer – add two for every doe that breeds this winter. It’s a very young herd overall, with many yearlings and two year olds, so we can expect rapid increases in the next few years. Our little nature preserve in the middle of the city is becoming an experiment in the effects of a booming deer population, with no end in sight!