The Annual Bighorn Reunion

Noise and power and the right to breed

I’m fortunate to live where I can take a short drive and observe and photograph bighorn sheep in their noisy rut, a mating ritual worth hearing and watching. The few weeks in November of energetic battling and well-timed breeding are the best chance I have to see adult males and females interact since the sexes typically live isolated from one another until the breeding instinct draws them to their annual reunion.

Though young male and female bighorns start their lives together in groups led by females, when a male is two to four years old, he leaves his mother’s group in search of older males. He will wander alone until joining a bachelor group, like the one pictured below, that lives apart from female-led groups. 

Females, on the other hand, remain in their mother’s group and adopt certain roles, according to one naturalist who studies bighorns. Some females are babysitters that watch the young while mothers go to feed. Others act as guards scanning for predators. One will become her group’s leader.

Those female-led groups and bachelor groups descend in late fall from the higher elevations and mingle in Yellowstone’s valleys. The male on the right in the photo below had approached the female, trying to sniff and sense if she was ready to breed. While females can breed when two to three years old, a male will not usually win the right to breed until he is six or seven, full grown, and packing a thirty-pound pair of horns.

The battle for breeding rights begins when two males—that may have lived in the same bachelor group—face off. They snort, rear up on hind legs, and charge at twenty miles per hour. They butt heads and clash horns with a whack that can be heard a mile away. The noisy contest can last several hours before a winner prevails.

One researcher estimates that the collision between two battling bighorns has a force ten times greater than a collision between two football players. While many helmet-wearing football players suffer concussions, bighorns don’t for several reasons. First, a bighorn’s brain is protected by two layers of bone separated by struts and cavities that act as shock absorbers. In addition, those horns are made of bone surrounded by a sheath of keratin, a material similar to our fingernails. That sheath yields a little during a collision and reduces the force of impact. Finally, during the battle, a natural process slows the return of blood from a battler’s head to the rest of the body. That additional blood volume swells the brain’s arteries and veins and creates a “bubble wrap effect” that helps keep the brain from banging around during butting.

Once battling subsides, breeding begins. Females mate with a sequence of partners; even a male who didn’t prevail at head butting may mate with a female once a dominant male moves off.

When the rut ends, the exhausted bachelors and pregnant females go their separate ways and live apart from one another until mating brings them together again. I’ll attend the next reunion too.

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I write and photograph to protect wildlife and preserve 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.

All photos by Rick Lamplugh.