Unlike domesticated livestock, bison have retained their deep coded wild genetics. Similar to other mammals of North America (elk, deer, and bear), the breeding and birthing seasons of bison are perfectly synched with their evolutionary past and dialed into Mother Nature's brilliant rhythm. From July through September, the Force of Nature bison are in full blown rut and the dynamics of the herd gets rather interesting around the ranch.
For those of you unfamiliar with the term, the mating season of certain mammals is known as the rut. The latin roots of the word literally translates meaning "to roar" and is characterized in bison bulls by increased testosterone production, exaggerated sexual dimorphism, increased aggression, and an obsession with females in heat.
During rut, mature bison bulls often mark themselves with mud, manure, and sometimes urine to make themselves more appealing to females. True to the translation of rut, the bulls fill the air with deep primordial roars that are not heard at any other times of the year. These vocalizations are often met by other males challenging each other for dominance. The result is many ferocious battles in which males use their horns to push each other into submission. With the dramatic increase in caloric expenditure, it is common for breeding bulls to sustain many injuries as well as lose up to 20% of their overall body weight during the rut! The physical demand of the rut ensures that the strongest and most adapted animals get to breed (thus carrying on the best genetics for the herd).
As with many other wild species, the bison rut is designed in Mother Nature's wisdom. With bison, the timing of the rut is established by the length of gestation for a female. Surprising to many, a bison's gestation length is the exact same as a human (40 weeks/280 days)! While the majority of breeding happens in August, this ensures that calves are born in the Spring. The brilliance of this evolutionary rhythm ensures that female bison are able to graze on the most nutrient dense grasses of the year while producing milk for their calves! Healthy grass equals nutrient dense milk!
As land stewards and bison wranglers it is important that we ensure that our animals have peak nutrition and health during the rut. Going into breeding season with nourished bodies dramatically improves the rate of conception and thus ensures more calves are born on the ranch during the Spring.
While we recognize that bison are perfectly able to kick our ass year round (again, they are not domesticated animals), we are especially cautious during the rut. While males are battling for dominance, they lose all sense of proprioception and will run each other into trees, vehicles, each other, and unsuspecting ranchers. Two fighting bulls making accidental contact with a human would be equivalent to getting run over by a freight train... something we try avoiding here at the ranch for obvious reasons.
So, as you enjoy the warmest months of Summer, take some time to appreciate the fact that bison are dialing up the heat and getting busy growing the national herd closer to 1,000,000 animals! It is through the important growth of the herd that we can positively impact more landscapes through planned grazing!