The Bison of Yellowstone ~ Yellowstone Forever Field Seminar Series, Part 2

It is 7:00 AM and the “Bison of Yellowstone” course is due to begin in a couple of hours.  There are a few of us mingling around the bunkhouse, enjoying our morning cup of joe.  As I look down the pathway to the cabins, I cannot believe what I am seeing.

I call over the students as I open the bunkhouse door.  A gorgeous bull bison, sporting a full beard, pompadour, and swaying pantaloons, is meandering down the walkway, heading for the bunkhouse.  His timing couldn’t be better!  He walks across the front porch and down the side of the building to the foot of the stairs at the back porch.  His behavior electrifies us as he grunts and snorts, then proceeds to urinate.  We believe he is agitated with us, as he trots off to the corner of the ranger residence next door.  He exhibits the same behavior there, then drops down, rolling in his urine.  As we look across Rose Creek, which runs through the ranch, another magnificent bull and the cow he is tending are watching, and this show is all part of the bull dominance so often displayed this time of year.  Welcome to the rut!

Beginning mid-July and continuing into the early days of September, the bison rut is on in Yellowstone.  Bulls do most of their communicating during this time of year, their breeding season.  Often during the rut the bulls could be heard from our cabins, snorts and bellows sounding more like a pride of lions.  It was eerie and exhilarating.

I watched from the bunkhouse as this bull was trying to tend “his” cow.
Here was his response to me when I opened the door to snap this photo. His bellow was hysterical.

During the rut bull bison focus their attention on the cows, trying to determine when they enter estrus, the time when they are receptive to breeding and can be impregnated.  A cow’s urine is full of information on when she is nearing ovulation.  The bull has a vomeronasal organ in the roof of his mouth than can analyze female urine and determine if she is receptive.  Sticking his nose into the cow’s urine,  he raises his head with upper lip curled, tongue reacting as if he is tasting a fine wine.  This action, called the flehmen response, is common in most ungulates.  We observed this behavior during our time in the field, after which the bull chased the female, a sure sign he felt she was ready.

So what does all this bull posturing mean during the rut?  Here are some of the questions that I had answered:

Q:  What does that raised tail mean?

A:  It could mean one of two things – charge or discharge.  When a bull or even a cow is agitated, they lift their tail into what looks like a question mark.  A raised tail is often seen on the bulls during the rut, as their testosterone levels keep them agitated much of the time.  As for the discharge, do I really need to explain that?

Two bulls…hmmm, wonder what that raised tail means? And what about that curled lip?

Q:  What’s all that rolling around in the dusty wallows about?

A:  All bulls wallow several times per day during the summer, probably ridding themselves of insects and perhaps reducing their body temperature.  No one knows for certain why a bull urinates into a wallow before rolling in it during the rut.  Perhaps he is showing his male dominance to other bulls, or is he trying to impress the gals?

Q:  How does a bull choose a female?

A:  Sorry guys, but the girl has the final say on who sires her calf.  The bull expends a lot of energy trying to “tend” a cow when he knows she is nearing estrus, but the cow is looking for a high-ranking bull, one who has been tested through a few winters, battles, predators, etc.  If she doesn’t think the guy lavishing her with attention is going to be a fit partner, she will take to running, prompting other bulls to chase her.  Who she ends up with may not be who she came to the party with.

Q:  Are bulls monogamous?

A:  Seriously, not even close.  Bulls are quite the cad, trying to impregnate as many cows as they can during the rut, in order to extend their lineage.  And if that wasn’t bad enough, they can’t be said to be good fathers either. After the rut bulls can be found alone, enjoying the warm sun, eating and ruminating, resting and preparing for the winter.  But I still love you guys!

A good-looking couple enjoying the sunshine in Hayden Valley

Q:  Now to the touchy subject of bison sex.  I don’t want to sound like a voyeur, but how does all that work?

A:  Don’t blink or you might miss it!  Bison sex takes a whole 4-5 seconds, with the bull putting his front legs over the flank of the female.  At the time of ejaculation, the force of his abdominal contraction is so strong that the bull is literally lifted off the ground, placing all 2,000 pounds of him on the cow’s back.  It’s no wonder that a cow can be seen limping for days afterwards.  It begs the question, can you blame a girl for not being that interested in sex?

Our bison class came upon this scene as we were heading to Hayden Valley to observe bison behavior. Two bulls were fighting for dominance, fur flying, stopping traffic.

Q:  How often during the rut do bulls fight, as in head-to-head combat, like we so often hear about?

A:  Surprisingly, bulls try not to fight with other bulls if possible.  They lose, on average, 200 pounds during the rut as they turn their attention to tending cows and having sex instead of eating.  Winter rapidly approaches after the rut, and they need as much energy as possible, stored as body fat, to help get them through the cold, harsh days.  Time spent fighting means time taken away from breeding and valuable energy expended.  Bulls try to modify another bull’s behavior instead, getting them to submit.  This is where all the posturing; e.g. grunts, bellows, rolling in wallows, stamping of hooves and shaking of pantaloons comes in.  The winners of this posturing don’t spare their rivals, rather themselves.  Some ecologists believe that it is typically the older bulls who are more likely to engage in battle to win the girl, as they have less to lose.   “An old bull is a bold bull”.

Because we have so much more to learn about these majestic creatures, doesn’t it make sense to preserve some wild spaces for studying them and other wildlife?

~  The Ends ~

If you are interested in learning more about the educational programs offered by Yellowstone Forever, go to www.yellowstone.org and check them out.  You won’t be disappointed.

Disclaimer:  The views expressed here are my own and do not necessarily represent the views of Yellowstone Forever.  

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