The Bison Breeding Ritual

Beautiful Moments Driven by Instinct

Using our car as a blind, Mary and I watched this male and female play their parts in the ancient bison breeding ritual—what many call the rut. We were amazed at the amount of energy that instinct drove both to expend. We were also excited; we had driven into Yellowstone’s Lamar Valley, past Soda Butte Cone, hoping to observe this ritual.

As we watched, we talked about what we saw and heard. First, of course, was the striking difference in size between the male and the female. The male has a much larger head and therefore a larger hump, that crane of muscle and bone needed to swing that massive head. Then there’s the male’s thick and seemingly styled top fur cascading between his larger eyes.

The female sometimes gently butted him in the ribs. He repeatedly grunted, even without her butting. Each grunt was accompanied by an impressive muscular contraction of his mid-body. She often grazed; he rarely did. She kept trying to go toward a nearby herd. He kept blocking her, keeping her isolated and protecting his chance to breed.

While males are able to breed when two or three years old, they usually don’t win the right to breed until six or so. Females, on the other hoof, can and do breed when two or three years old. From mid-July through August groups of soon-to-be ready females stream into the Lamar Valley. As the valley floor grows crowded with females, some with calves born just months ago, males mosey in by ones and twos. 

Once males and females are in the valley, the breeding ritual commences. To win the right to mate, a male—whatever his age—must prove his dominance. This male, arising in a cloud of dust from a wallow, intends to convey to other males his strength and energy. 

Males have other relatively safe ways to show dominance. They can grunt, bellow, and roar to deter other suitors and claim females. They may decide who is tops by moving alongside each other in a “parallel walk” or launching into a head-to-head shoving match.

But if posturing, walking, and shoving don’t deter a competitor, it’s time to rumble. Two contestants will dodge and feint, butt heads, and shove each other with their powerful legs. An experienced battler may slam a contender in the side with his massive head and sharp horns. At some point, one of the fighters calls it quits. Both loser and winner can sustain injuries that may be one reason male bison don’t live as long as females.

While we didn’t see this male battle another male, we were lucky to see this heartwarming and peaceful moment as the male and female stood, side by side, calmly sharing a drink.

A different male and female revealed yet another aspect of the rut. This big male had picked up the scent that indicates this female may soon be ready to mate. But her months-old calf was still at her side. We watched the male repeatedly try to come between mother and calf. But the calf, driven by instinct, kept running back to its mother’s side. Quite the workout for everyone. 

However much a male desires a particular female, the final decision to breed is hers. As she nears breeding time, she may elude a persistent suitor and run through the herd to attract other males. She may approach a larger, more dominant male (like the one pictured above) and permit him to breed with her. In this way, females enable some of the biggest, strongest, and most alert males to pass on their good genes and improve the herd one calf at a time. Natural selection in action.

Once genes have passed and the rut concludes, each male will depart to spend winter alone or with a few other males. If weakened by an injury or by not grazing during the rut, a male may succumb to winter or wolves. The pregnant female will merge back into her small matriarchal-led group. On meager forage she will sustain herself and a developing fetus through the ravages of winter. Then after nine to nine-and-a-half months, the calf will arrive—the marvelous result of this incredible ancient breeding ritual driven by instinct.

Thanks for being part of Love the Wild! I write, speak, and photograph to protect wildlife and wild lands. My bestselling In the Temple of Wolves; its sequel, Deep into Yellowstone; and its prequel, The Wilds of Aging are available signed. My books are also available on Amazon unsigned or as eBook or audiobook.

Photo Credits: Photos by Rick Lamplugh