Rut (mammalian reproduction)

The rut for white-tailed deer (Odocoileus virginianus) usually lasts three weeks in the Northern Hemisphere and may occur most of the year in tropical zones. The rut is the time when white-tail deer, especially bucks, are more active and less cautious than usual. This makes them easier to hunt, as well as more susceptible to being hit by motor vehicles.[5]

Outdoors writer Charles Alsheimer has done research demonstrating the white-tailed deer rut is also controlled by the lunar phase and that the rut peaks seven days after the second full moon during October and November (the rutting moon),[6] while elk begin rutting during the September equinox on 21 September.

A white-tail doe may be in estrus for up to 72 hours and may come into estrus up to seven times if she does not mate. Cows may come into estrus up to four or more times if they do not mate.

The rut can start as early as the end of September and can last all the way through the winter months. Bucks usually begin this process when the velvet is falling off their antlers, and it can last all the way until they start to shed their antlers. The peak of the rut, however, is right in the middle. The average peak day for the white-tail rut in the U.S. is November 13.[7] Around this period of time, the bucks and does are very active, with the rut in full swing. For a hunter sitting in a tree stand at this time of the year, it is not uncommon to see many deer pass through his specific area, due to other deer chasing others.

White-tailed bucks in late rut in the Great Smoky Mountains

There are many behaviors a buck will exhibit during the rut. During pre-rut, bucks will spar with each other. Sparring is low-intensity aggressive behavior, involving mostly pushing and shoving. Bucks of different sizes will do this to each other. After pre-rut is finished, a buck will rub his antlers on a tree (thus making a "rub"), and make scrapes on the ground with his hooves: both of these are ways a buck will mark its territory and proclaim his dominance for other bucks to see. These activities are usually done at night.[8]

The most prominent behavior of all during the heat of the rut is fighting, where bucks show their true dominance to others. In fighting, bucks usually battle against similar-sized deer, and small bucks do not normally challenge mature large ones: more often than not, smaller bucks fear the more mature bucks and leave or avoid the dominant deer's territory. The fights can go on and on, with the winner getting the group of does. Some fights go on until death, and if not, it is not unusual to see one of them get injured.

The energy expenditure of chasing and fighting during the breeding season can result in a buck losing an immense amount of weight, with some research documenting losses of as much as 20% of body weight. On average, a buck before breeding season can weigh up to 180 pounds (82 kg). After he has gone through the stages of the rut, he can lose about 50 pounds (23 kg) of weight, which is quite large, especially for only a few months of time. In the post-rut, a buck will need to replenish his body and catch up on the weight and energy he has lost.

Sources[9] have stated that after the rut, a buck will go to a bedding spot and will remain "motionless" for a large amount of time, even to the extent of about two days, as he is thoroughly exhausted. After he has rested, he will get up and start to feed extensively, trying to catch up on all the nutrients his body requires. Croplands have much high carbohydrate grain in them, and a buck can be found here often, eating and getting nutrients. When the climate is extremely cold, a buck will sometimes resort to swamps and bogs, because of the warmer temperatures these areas hold.

The timing of the elk rut depends on where they live. In the Northern Hemisphere, it occurs between mid-August and mid-October. In the Southern Hemisphere it occurs between mid-February and mid-April.

The rut tends to last somewhere between 20 and 45 days.[10] This varies on latitude, which affects the timing of spring and autumn and which can give elk a longer calving season and a longer rut.[11] During the rut, elk frequently use areas around fresh water, and tend to bed in heavy timber five to six hours per day.[12]^: 579 A cow elk will remain in estrus for 12 to 15 hours, if they are not bred during this time frame they will normally have another estrus cycle 18 to 28 days later.[11]

Elk use several different vocalizations during the rut. Some are made only by a certain sex or age class, and each is used for a different reason. The first of which being the cohesion call which is made by both sexes of elk, and is used to locate one another.[13]^: 225 An alarm squeal is made by both sexes of elk when they are on alert, during the rut these are used frequently by young bulls (male elks) being run off by the herd bull.[13]^: 228 Satellite bulls frequently spar with one another during the rut, and in turn make sparring squeaks.[13]^: 228

A bugle is a vocalization made exclusively by bulls. The typical bugle consists of three acoustic parts, a low frequency "on-glide" that sounds guttural in tone, which then ascends into the highest frequency part of the call termed the "whistle", and the last portion of the call, the "off-glide" that returns to a low-frequency tone.[14] The function behind this acoustic structure of the bugle is directly correlated to the male's physiology and how different frequencies travel through varied environments.[15][16] In terms of physiology, the larger an animal gets the lower frequency of sound it is able to produce.[17] This is because with an increase in size comes an increase in vocal fold length, and longer vocal folds confer an increased ability to produce lower frequency sounds.[17] Because of this relationship, a bugle can be directed toward other bulls or toward cows to demonstrate the size and thus fitness of the bull vocalizing. A bull will direct his bugle toward his cows while gathering them or while chasing an estrus cow. A herd bull will direct his bugle toward another bull to express his dominance over the herd, while a satellite bull may use his bugle to challenge the herd bull.[13]^: 229 The reason for the high-frequency portion of the bugle is due to the propagative efficiency of differing frequencies through varying environments. Studies have shown that as a bull's harem increases in diameter, meaning the cows become more dispersed, he tends to vocalize more frequently than if they were within closer proximity.[18] The higher-pitched section of the call propagates through the environment better, which is why the bull uses it to congregate a harem that is becoming more spatially dispersed and thus harder to defend.[18] Acoustic analyses comparing bull elk bugles with cow elk cohesion calls show a notable degree of acoustic similarity, indicating that both vocalizations may perform a congregating function, which is why the bugle is often used by the bull to condense his harem.[18]

The ability to produce such a high-frequency vocalization by such a large animal is unusual.[19] As explained above, this is because larger body mass positively correlates with longer vocal folds and thus lower frequency emission. Larger body size also corresponds with a decreased ability to emit high frequency vocalizations.[19] Bull elk overcome this by a unique anatomical mechanism that produces sound using a different pathway than the vibrations of the vocal folds.[20] Bull elk constrict their supra laryngeal vocal tract, specifically in the nasal cavity in order to create a smaller opening for exhaled air to pass through.[20] As air moves through this opening it causes the tissues to vibrate and produce the high frequency sound waves which comprise the "whistle" portion of the bugle.[21] This anatomical development for bioacoustics in elk was discovered upon sonographic analysis of bugle vocalizations which revealed a biphonetic (two simultaneous frequencies) display.[20] One frequency was high (the result of the supra laryngeal constriction), and the other was low (the result of normal vocal fold oscillations).[20]

Yelping also known as "grunting" is usually only made by herd bulls when they are excited. They are made more often while interacting with cows than with other bulls. "Yelping commonly was accompanied by contractions of the penile region with simultaneous emission of short spurts of urine."[13]^: 230

The rut has six phases: the pre-rut, the first breeding phase, the first rest phase, the second breeding phase, the second rest phase, and the third breeding phase.[11]

• The pre-rut takes place from mid-August through the beginning of September. During the pre-rut bulls begin bugling and gathering their herds. Bulls will bugle to attract cows as well as to express dominance over other bulls. A "herd" bull is the dominant bull in a herd. Younger, smaller bulls are known as satellite bulls, as they tend to cling to the edges of a herd trying to pick up any cows willing to leave the herd. Larger satellite bulls will challenge the herd bull to try and take control of the herd. These challenges include a good deal of bugling as well as fighting.[11]
• The first breeding phase of the rut takes place between the beginning and the middle of September. This is when the three year and older cows come into estrus. During this time herd bulls bugle to keep their cows close by, they also answer the bugles of satellite bulls to let them know they are still dominant. A herd bull will also bugle while approaching a cow in estrus so the cows become familiar with his bugles.[11]
• The first rest phase of the rut occurs between the middle and the end of September. At this time the older cows are predominantly out of estrus and the younger cows have not yet come into estrus. During the rest period, satellite bulls will try to join the herd while the herd bull is resting.
• The second breeding phase of the rut takes place three to four weeks after the first breeding phase. This is due to younger cows coming into estrus, as well as older cows that were not bred on their first estrus cycle coming back into estrus. Herd bulls are less aggressive towards satellite bulls at this phase in the rut due to exhaustion.[11] The second phase of the rut may have the most bugling activity due to the combination of the testosterone levels of the younger bulls rising, and the herd bull still trying to maintain control of the herd.
• The second rest phase of the rut occurs around the middle of October. By this time the original herd bull usually does not have control of the herd, due to a great decline in physical condition. Terry Bowyer states, "Elk were observed feeding in the following percentages of observations: master bulls 24%; bachelor bulls 53%; yearling males 62%; cows 64%; and calves 62%" (Bowyer uses the terms "master bulls" and "bachelor bulls" which have the same meaning as "herd bulls" and "satellite bulls").[12]^: 577 Herd bulls do not have time to feed during the rut due to constantly fighting other bulls as well as chasing and breeding cows.[11]
• Occasionally a third breeding phase will occur. This will usually take place around the end of October or early November. This is a result of yearling cows coming into estrus for the first time or two-year-old cows coming into a second estrus cycle. Since most of the herd bulls have left the herd by this time of year, the breeding is usually done by the younger satellite bulls. After this phase the rut is over, most bulls will leave the cows and form bachelor herds to spend the winter with; however young bulls will usually remain with the cows throughout the winter.[11]

The fallow deer (Dama dama) is an ungulate which employs an unusual strategy for mating during the rut. This strategy is the creation of a lek, a display area presented to the females where the males gather and allow the females to choose a mate based upon their traits alone while reducing predation risk, disturbance to copulation, parasite transmission and the cost of looking for a mate.[22][4] When females come to the lek they leave soon after mating but the males will tend to stay in the lek to court other females until the end of the rutting season.[23] However, male fallow deer which are unsuccessful in mating will leave the lek sooner than other males and they will adopt other strategies to compensate for their lack of mating success in the lek. Furthermore, the duration spent in the lek is positively correlated with the behavioral traits of male display frequency and aggression, male hierarchical position and secondary sex characteristics such as antler size.[24] Overall, lekking species such as the fallow deer have a short intense rutting season where the males face intrasexual competition, territory defense and management of females within their territory.[25]