Breeding During the Whitetail Rut
The pre-rut is the time before deer mate with one another. During this time, deer exhibit a dramatic change in behavior. Early on, does and bucks can be seen grazing together; this is the only time of year they are seen side by side. As the pre-rut progresses, deer also become aggressive towards each other. For example, mother does will drive their young away and seek isolation, while bucks will challenge any other buck they encounter. This aggressiveness causes the deer to become careless of their surroundings, which makes this an ideal time for hunting.
The breeding season begins in early autumn, and lasts until the beginning of December depending on region. The shortened fall days raise the hormone levels in deer, which drastically alters their demeanor. There's a buck's testosterone, and a doe's estrogen.
During the pre-rut, estrogen prepares the doe's internal organs for birthing. It also causes emotional changes in her such as aggressiveness, intolerance, and isolation. This need for isolation causes the doe to disperse her fawns. She no longer allows the fawns to drink from her; often pushing them away and seeking seclusion.
The doe will not tolerate her male fawns; driving them out of the deer herd. This prevents any inbreeding between the mother and son. Female fawns will also wander, although they never stray from their home range. This makes it easier for a buck to find a doe. However, not much else changes in the doe's life during the pre-rut.
On the other hand, bucks undergo much greater changes. These changes begin with the shedding of the velvet. Testosterone is the hormone responsible for antler growth. As the level of testosterone increases, the antlers mature and stop growing. This rise in testosterone also causes the antlers to harden. After the antlers mature, the velvet which covers them dies and becomes dry. The dried velvet irritates the buck, who will try to rub the velvet off on trees and other protruding objects; this process is called rub-off.
Rub-off also helps bucks estimate the size of their antlers, since they can't see them. Often times, a buck will be seen rubbing his velvet as well as his forehead. This is often done in order to leave behind a scent from a deer gland on the forehead. Researchers are unsure of the purpose of this scent. However, they are sure that rub-off serves a reason other than removing the velvet, since if left alone, the velvet will eventually come off by itself.
As testosterone levels increase, tensions begin to rise among buck herds. The male deer begin to separate themselves from the social herds they formed over the spring and summer. The bigger and older bucks may wander outside their home range in order to find a mate. They have reached their peak weight, and the increase in testosterone has caused other changes, such as an enlarged neck and enlarged sex organs. This is the time when the massive and majestic buck of hunting lore can be most easily found.
Eager to test their new antlers, bucks will engage in sparring. Sparring is a sport which helps establish and confirm the dominance hierarchy of the bucks in the area. It also helps bucks gauge how large their antlers are. Sparring begins with one buck approaching another with his head lowered. If the other buck accepts the challenge, he too will lower his head and the two bucks will lock antlers. They will then push each other until one buck overpowers the other. The losing buck may lick the winner's forehead and face in order to remember the winner's scent. The loser now remembers this buck to be dominant over him.
Sparring is most often done between bucks of different herds, since the hierarchy of herds is usually formed during the summer. It should be noted that sparring is not fighting; sparring is a gentle sport between two, sometimes three, bucks. Often times, older, larger bucks will offer one antler to younger bucks for them to spar with. Sparring matches performed early in the pre-rut are thought to strengthen social bonds among bucks. However, as autumn continues, sparring becomes more frequent and aggressive.
The hierarchy formed among bucks helps establish the breeding rights. It is the dominant bucks that get to mate the most. Most of the time, the dominant bucks are the larger, older bucks, and the ones with the strongest genes; they are typically the most aggressive also. This is nature's way of insuring that the new generation of deer acquires the best genes for survival.
The interesting thing about dominance is that it does not follow a linear structure. Imagine you spot three bucks. It is possible to have a situation where buck #1 is dominant over buck #2, buck #2 is dominant over buck #3, but buck #3 is dominant over buck #1. However, it is usually the case that there is one buck who is dominant over all the other bucks in an area.
During the pre-rut, bucks will also engage in an activity called signposting. Signposting is used to signal other does that the buck is in heat, and to warn rival bucks to stay away. Bucks use their glands to deposit scents which carry this information. There are two types of signposting: deer scrapes and buck rubs. These two are almost always found near each other, and are usually found on trails which deer often travel. Older bucks will scrape and rub earlier and more often than younger bucks.
Scrapes are most often found under tree branches. Bucks lick these tree branches and rub them with their forehead in order to deposit scents from the deer's forehead gland, their pre-orbital gland, and their saliva. The buck will then scrape the ground beneath the branch, leaving a pawed area about 3 to 4 feet wide. While making the scrape, scent will be deposited from the interdigital glands. The buck then rub-urinates in the scrape. The scent from rub-urinating is very strong, often strong enough for a human to smell.
Deer scrapes are often found on higher ground; this helps disperse the scent across a wider area. One buck will leave many scrapes in one area, but he will not deposit them across a large range. The scrapes of a buck are usually done within a quarter-mile radius of each other. If a doe wishes to respond to this calling card, she will urinate near the scrape. This tells the buck that there is a doe in the area that is ready to mate.
Buck rubs are marks left on trees as the buck uses his antlers to strip away the bark. He also rubs his forehead against these trees to leave a deer scent. The white, bark-less portion of the tree also serves as a visual sign to other deer. A buck prefers to rub on aromatic trees, such as pine, cedar, and cherry; the natural odor of these trees helps disperse the scent of the buck. Older bucks have thorns, or little bumps, at the base of their antlers, which help to strip the bark away.
Deer enter puberty depending on their weight; once a fawn reaches 75 pounds, it will usually enter puberty. Some yearlings and fawns take part in the breeding season. If the fawn has been leading a healthy lifestyle during the spring and summer, it will have a good chance of entering puberty during the pre-rut. However, male fawns are seldom given a fair chance to breed because the older bucks will scare them away from does, or, older does may be reluctant to breed with them. In contrast, if a female fawn does breed, they will usually bear only one child.
The Deer Rut
The actions and aggressions of the pre-rut occur in order to satisfy the deer's desires during the deer rut. The rut is the period when bucks actually breed does. This breeding phase usually lasts about a month; in most parts of the country, the rut occurs in November, although this varies depending on geographic location.
However, does are only able to breed during a certain time, called estrus. The estrus cycle lasts between 2 to 4 days, and it is the time during which a doe's body is able to mate. A hunter can sense the rut approaching because he will see more buck movement; especially during daylight hours.
A buck chooses his mate by first checking his signposts to see if any doe has responded. A doe responds to a signpost by urinating near it. If the buck smells the urine of the doe, he will attempt to find her. By smelling a doe's urine, a buck is able to tell if she is close to estrus or not. Bucks will usually ignore does who are not close to estrus.
Bucks are often able to find receptive does because they seldom stray from their range. Instead, they stay within this range, as if pacing. Once a buck finds her, he will make short dashes at the doe, accompanied by short grunts and wheezes. Other subdominant bucks may join in the chase, but it is always the dominant buck that is in the lead. Researchers believe this behavior triggers the doe estrus cycle of the doe. A doe is usually calm and receptive to any buck that approaches her, although she may sometimes get the best mate by running away from the younger bucks.
Eventually, the doe allows the dominant buck to approach her. The two will seek to isolate themselves from the other deer. She urinates; the buck analyzes the doe urine using his sense of vomolfaction.
If the buck's analysis reveals that the doe is close to estrus, he will once again proceed to follow her, this time in a more subdued manner than before, with his head low and neck outstretched. The buck will follow her like this for an extended amount of time, often for as long as a day, maybe longer. Many bucks become impatient and eventually leave the doe. This is another way to insure that the strongest bucks are the ones to mate, since younger bucks are the most impatient.
A short while before estrus, the doe will allow the buck to approach her; this is called "tending." The buck will watch for other rival bucks while he “tends” the doe; waiting on her to come into estrus. If he spots other bucks in the area, he will chase them off. The buck only chases them for a short distance, since he is cautious not to leave the doe for too long. A buck will even drive away the fawns of the doe.
Sometimes, a buck will be faced with a buck that does not back down from his threats. In this case, a fight usually ensues. Both bucks will face each other before repeatedly clashing their antlers. This continues until one buck surrenders. The victor is the one that will breed the doe. These fights are usually short lived but can result in severe injury to both bucks involved. Sometimes, death can be the end result of a fight when antlers become locked. Other times, although a buck may win a fight, he may be too tired to continue. In this case, an onlooker may move in and mate with the doe. Still, buck fights are rare, since the dominance hierarchy is already established.
As a doe approaches estrus, she urinates frequently. When she does enter estrus, the buck will mount her and begin the breeding process. With the buck resting his chin on her back, the doe supports most of the buck's weight. The doe and buck mate several times while she is in estrus. When her scent no longer appeals to the buck, he will move on and search for a new mate.
As autumn winds down and snow begins to fall, the hormone levels in deer decrease. Deer then return to their normal routines. Bucks begin reforming their social group (although, these are often times not the same group they had during the spring and summer), and does carry the seeds which will bloom into fawns come spring.
The deer rut usually leaves the dominant bucks tired and depleted of fat reserves. They look smaller than they did just a few short months ago. A buck may lose about 30% percent of his body weight during the rut while chasing does as well as the competition. Therefore, bucks must spend the time after the rut replenishing their body for the brutal winter that lies ahead. Sometimes, the dominant buck in an area will die because it can't replenish itself before the harsh winter sets in.
During the post-rut, does are in much better shape than the bucks. However they too will spend this time eating and growing their fat reserves for the winter. They must also eat more to provide nutrients for the fawn growing inside them.
Some does are unsuccessful in breeding during the first month of the rut. Those that aren’t will come into estrus again about a month later. These does may find a younger buck to breed with, perhaps one that did not have a chance to breed during the first breeding phase. Many fawns come into puberty at this time, and as a result, are able to breed.