Rolling Thunder-The Bison Rut in Hayden Valley

For some it would be the grizzly bear, for others perhaps the wolf or the elk, but if I had to choose an animal to symbolize Yellowstone and the American West, it would be the mighty bison.  I’m a bit partial to these magnificent creatures who will always hold a special place in my heart.  Majestic and powerful, bison have been revered by Native Americans for centuries. As I look around my home decorated with sculptures, paintings and photos of bison, I am the first to admit that I too am under their spell. Not surprisingly, bison are one of my favorite animals to photograph and each year I look forward to seeing the herds gather together in Yellowstone during the summer months.

Watching the bison in Hayden Valley, I imagine what it must have been like hundreds of years ago when the great herds stretched out as far as the eye can see.  As recently as 1800, bison roamed North America from coast to coast, with population numbers reaching  more than 50 million. Numbers dwindled rapidly during the extermination of the great herds by buffalo hunters and by 1889 only 542 bison remained.  Thanks to the efforts of conservationists working diligently to save them, the bison population now holds steady at approximately 150,000 on both public and private lands, including a healthy population of over 3,500 living in Yellowstone.  Within Yellowstone, the bison herd is divided into two distinct sub-herds. The Northern Herd is comprised of approximately 2300 animals and ranges from the north entrance at Mammoth Hot Springs through Blacktail Plateau into Lamar Valley. The Central Herd, comprised of 1400 animals, ranges from the Madison River Valley into Hayden Valley and the Upper and Lower Geyser Basins.


The grandeur of the bison herds migrating through Hayden Valley makes me think of what it might have been like when millions of their kind roamed North America. It saddens me that we will never see them as they once were before they were so savagely slaughtered, but to experience their strength and majesty in this little oasis of Yellowstone always leaves me in awe. (Sandy Sisti)

A bull bison stands watch over the herd gathered in Yellowstone’s Hayden Valley.


Each year, as spring turns to summer, I wait patiently for the Central Herd to return to Yellowstone’s Hayden Valley. Bull bison, who live in small bachelor herds or remain solitary for most of the year, begin to gather in the valley in May. Here the bulls will remain until the cow/calf herds join them later in the season. These maternal herds travel from calving grounds outside the park to summer in Hayden Valley.  Their journey starts in late May as these family groups navigate along the Madison River, through the Mary Mountain Trail to their final destination along the Yellowstone River.


Young bison calves are reddish brown in color. At about two months of age, the calf begins to develop a shoulder hump and horns and also begins to turn dark brown. At four months, calves are entirely brown and more closely resemble their mother.This young calf reunites with his mother after crossing the Madison River in Yellowstone National Park.  "Nose to Nose" was published as the cover image for the Fall 2012 Defenders Magazine, the voice of Defenders of Wildlife. This image was also the featured photo for May in the 2012 Buffalo Field Campaign "Wild Bison" Calendar. In addition, "Nose to Nose" was named as one of fifty contest finalists in World Wildlife Fund's 2011 "Life Grows On" Photo Contest. (Sandy Sisti)

A bison cow and calf greet each other after crossing the Madison River en route to their summer range in Hayden Valley.


Cows and calves arrive in late June, just in time to feast on the greening grasses and sedge covering the valley floor.  For a while, all seems peaceful as bison calves tussle together in play groups while adults doze in the midday sun.  The mood changes rapidly and by mid-July, the deep, rumbling sounds of bull bison in rut can be heard throughout the valley.


Bellowing and pawing the earth, this large bison bull prepares himself for battle during the summer rut.  During this time of year, the largest of the bulls go head to head to determine who will sire next year's calves. (Sandy Sisti)

A bull bison bellows towards his rival as the summer rut begins.


Watching these one ton bulls paw at the earth, dust-up in wallows and battle for the right to breed during the rut is an incredible sight. Like other ungulates, bull bison rarely fight, but when they do it is such an amazing display of power that you can almost feel the earth shake. Battles start when a challenger approaches a dominant bull who warns away his rival by swinging his horns, bellowing and pawing the ground.  If these tactics don’t deter the challenger, the two then clash head to head. When fighting, the goal of each bull is to hold his opponent’s head between his horns. Failure to hold the horns in position can lead to goring of the opposing bull’s neck.


As August approaches, bison bulls begin to spar for the affection of females in the herd.  The largest bulls battle first and begin "tending" females, leaving smaller bulls to breed later in the season with females who have yet to be claimed. (Sandy Sisti)

A dominant bull bison chases a rival from the cow he is tending.

Two bull bison battle for dominance in the thick fog of Yellowstone National Park. (Sandy Sisti)

Two bulls battle for dominance in Yellowstone’s Hayden Valley.

During August, the deep, rumbling sounds of the bison rut can be heard throughout Hayden Valley as these one-ton giants gather for this annual ritual. These two bulls go head to head to determine who will sire next season's calves. The best this young calf can do is to get out of their way so as to avoid injury. This image is the featured image for August in the 2013 Yellowstone Association Calendar. This image was published in the December/January 2012 issue of National Wildlife Magazine. This image was also published in Buffalo Field Campaign's 2011 Wild Bison Calendar. This image was named one of ten contest finalists in the 2010 Defenders of Wildlife Photo Contest. In addition, this image took the first place prize in the 2008 Wyoming Wildlife Magazine Photo Contest "Color Wildlife" category. (Sandy Sisti)

A bison calf runs for cover as two massive bulls collide.


Most battles end up with the defeated bull withdrawing in retreat, but bulls sometimes die from the injuries they sustain during these violent clashes.  In fact, so many bulls perish from the ravages of the rut, that they have become an important late summer food source for grizzly bears and other scavengers within the confines of the Park.


 (Sandy Sisti)

Bulls are sometimes mortally wounded during battle.


When the fighting has ended, the victorious bull returns to the cow he has been “tending”.  The bull remains with the cow until she is ready to breed and once bred, he moves on to another cow. As mid-August approaches, battle-weary bulls begin to leave the breeding herds and return to their solitary ways.  This gives smaller, less dominant bulls a chance to breed with the remaining cows.  The rut continues into September, but after a while, it starts to quiet down- leaving me waiting for next year when these one ton giants will once again do battle in the wilds of Yellowstone.


A lone bison bull stands silently along the banks of the Yellowstone River during the summer rut. This large bull has most likely bred  and is leaving the herd to once again lead his solitary existence. (Sandy Sisti)

After breeding, bull bison once again return to their solitary existence.






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  • Nancy Kendrick

    Wonderful bison images……….as usual!! Love your write-up too! We haven’t been to the park since fall 2011, and really need to get back! Your photos always make me want to jump in the car and get there now! Thanks!

    • sandysisti

      Thank you so much, Nancy! It really is great to spend time with the bison. It sounds like it’s time for you to plan a trip to Yellowstone soon so you can see them. Best regards!

  • David Douglas

    Greatly enjoyed your blog. You need to do more of them for us Yellowstone dreamers. I have a two week trip to the park planned for January, my first winter visit. The first week will be with Max Waugh. Stay safe in the fires.

    • sandysisti

      Thanks so much, David! I made a deal with myself to try to write a blog each month, but writing is like pulling teeth to me so I don’t think I’ll be keeping up my end of the bargain! Hope you have a great trip to YNP with Max. He’s such a nice guy. Steve and I usually go to YNP in January so maybe we’ll run into you there. Best regards!

  • docerr

    wow, just read this and your blog. You write just fine! Sorry its tough for you. I live in the Great Smoky’s. I loved your article about the Dunraven sow! I just read a book, bear in the backseat, by a retired ranger here in the smoky’s, one of the stories is about a black bear named Brutus that was relocated away 10 times and even into Virginia, in total he had traveled over 1500 miles trying to get back home and many times made it. So maybe the Dunraven sow was up North and made it back or has ventured to unknown lands. loved the bison article and pics

    • sandysisti

      Thanks so much. I would like to think the Dunraven sow was still with us, but I’m doubtful.