Pronghorn, unique to North America, are often mistakenly called antelope due to their similar appearance and ecological role. They are the only surviving member of the Antilocapridae family. Their yearly breeding season, known as the “rut,” is essential for species continuation.
Understanding the Rutting Period
The pronghorn rut typically begins in late summer and extends into early fall. In many areas, bucks start preparing for the rut in mid-August. The peak breeding activity usually occurs in September. This active phase can last for several weeks, sometimes extending into October.
Timing varies across their extensive range. In northern regions, breeding might occur from mid-September to October, while southern populations may experience the rut earlier, from July to October. The rut is a period of intense activity, with dominant bucks actively defending their harems.
Pronghorn Rutting Behaviors
During the rut, male pronghorn, known as bucks, display behaviors to establish dominance and attract females. Bucks will guard harems of three to five does, actively protecting them from other males. Females may temporarily join different groups, assessing males before mating, and sometimes mate with multiple males.
Territorial displays are common. Bucks mark their domain using scent glands beneath their ears and on their jaws, rubbing them on grass and shrubs. They also create scrapes on the ground, urinating and defecating to mark territory.
When confronted by intruders, dominant bucks may vocalize with a snort-wheeze, engage in staring contests, or head thrashing. If intimidation fails, males will engage in physical combat, locking horns and pushing against each other in intense but typically short battles. These confrontations can sometimes result in injuries.
What Triggers the Rut
The primary trigger for the pronghorn rut is photoperiod, which is the change in the amount of daylight within a 24-hour period. As summer transitions to fall, the decreasing day length signals to the pronghorn that it is time for the breeding season. This environmental cue initiates physiological changes within the animals.
Sensory nerves in the pronghorn’s eyes detect the shortening daylight hours. These signals are then transmitted to the brain, which in turn influences the production of specific hormones. In males, this leads to an increase in testosterone, which drives their aggressive and territorial behaviors. Similarly, in females, hormonal shifts, including estrogen, prepare them for breeding. While photoperiod is the main regulator, other environmental factors like temperature may also play a role, but the consistency of the photoperiod ensures the rut occurs at a predictable time each year.