Tuesday, January 15, 2013

One Wolf in a Bison Herd - Yellowstone Reflections

A lone wolf surveys a bison herd at Yellowstone National Park
The fourth and last wolf we saw in our summer week at Yellowstone National Park was wandering in a bison herd. We first saw the wolf cross the East Entrance Road from the shoreline of Mary Bay on Yellowstone Lake and then immediately trot into a herd of bison on the other side of the road. The bulls, cows and young bison did not stampede when the wolf walked among them. They kept grazing and resting, belching and rolling in the dirt. The wolf slowly trotted through the herd of about 40 bison, occasionally stopping or changing direction, and constantly looking around.

As the wolf approaches, a bison cow stands up and lifts her tail.

At one point, when the wolf approached a small group of reclining bison, a cow stood up and stared at the predator. The wolf changed direction, but then angled back to get closer all the while never looking directly at the alert cow. The cow slowly stomped towards the wolf with her tail held erect in a stiff arc. The wolf responded by looking away towards the distant edge of the herd and then it started to dig.

Bison heads towards wolf still holding her tail erect.
Wolf starts digging as bison approaches.
The digging seemed impromptu and distracted. When I asked the Lion Hunter why the wolf suddenly switched to digging, he said "displacement behavior" which I guessed to mean the wolf was pretending to hunt for small ground prey as a way to appear nonthreatening to the advancing thousand-pound herbivore. When the cow was close, the wolf stopped digging and looked directly at her for a few seconds, then casually trotted away to observe bison in another sector of the herd.

Wolf briefly faces bison before . . . 
. . . retreating.
At one point, the wolf passed within a few feet of the heavy horns of a large bull. The bull never showed any aggressive behavior, no charges, no aggressive tossing of its head or pawing of the ground. Another large bull reclining nearby didn't even get up or turn its head as the wolf passed. Again, the wolf appeared to avoid looking directly at the bulls until it was past them, and it repeated the digging behavior.

Wolf approaching two bison bulls.
Wolf passing in front of bull.
Wolf passing to the side of two large bull bison.
Recently I looked up the phrase "displacement behavior" and learned it means: "A seemingly irrelevant display of behavior given in conflict situations where it has no direct functional significance" (Wittenberger). It is often used to describe unusual behavior such as excessive grooming or pacing of pets or captive animals under stress, but it is also used to describe behavior of wild animals such as a bird stopping combative advances on a rival male to peck at a blade of grass. Displacement behavior may occur when an animal is uncertain about choosing between two conflicting responses such as aggression and fear.

Wolf digging next to two bison bulls.
Wolf surveying the bison herd again.
Finally, the wolf meandered behind a low rise and we did not see it again. By their actions, it appeared that the bison were not concerned about a solo wolf. And the wolf was intent on observing many individuals in the herd but not arousing any defensive behavior.

Later, I read that wolves often follow a regular route that provides them with good viewing opportunities of the herds and habitats frequented by prey within the pack's territory (McNamee). By this constant checking, they may be assessing whether individual prey have changed condition in a way that makes them more vulnerable to predation. If a wolf notes an injured or inattentive individual, it may bring back the pack to test the individual. This single wolf wandering and observing in the bison herd seemed to be exhibiting this type of "shopping" behavior.

The 31 wolves reintroduced to Yellowstone in 1995 and 1996 were captured from an area in Alberta,  Canada that did not have bison. In 15 years, some of the packs have made bison part of their prey base. Bison are primarily taken by wolves in Yellowstone in the winter when the wolves drive them into deep snow (Smith and Ferguson).

A mature bull bison at greater than 1800 pounds has few predators to fear in the summer.
The bison herd at Mary's Bay may not have been threatened at all on that summer day and the solo wolf may have been practicing its prey search behavior on the bison herd or not. There's only so much a casually observing human can interpret but it makes for a fun day outside.

This is part of a series of posts on wildlife observed in Yellowstone National Park in September 2012. To see more posts, select "Yellowstone" in the Sightings box in the right column. Please note that we were not close to the bison - these photos were taken with telephoto lenses and cropped. Bison can be dangerous and unpredictable and people should only observe them at a distance.

McNamee, Thomas, The Return of the Wolf to Yellowstone, Henry Holt and Company, 1998.

Smith, Douglas W. and Gary Ferguson, Decade of the Wolf: Returning the Wild to Yellowstone, Lyons Press, 2005.

Wittenberger, J. E., Animal Social Behavior, 1981 in


  1. Very cool. Some thoughts you may know already... There could be more going on there than just displacement behavior. The lack of eye contact is one tell - looking you in the eye is something a predator does to anticipate how you'll react. Where you'll run. Purposefully not making eye contact can be a sign of submission, but also a ruse - the "no really - I'm not sneaking up on you" ploy. And then there's the digging. When I was in the Okavango, and we'd come into elephant herds, the eles would similarly square up to us. But then the guides would get out of the trucks and purposefully not make eye contact while grabbing and tearing at leaves and branches on trees. Very quickly the eles would relax with a "oh - you're just a browser like us" response. And soon after that the curiosity would kick in and the young ones would wander over to try and figure us out. It was pretty amazing.

  2. I try the "I'm just another browser hanging out in the grassland, pay no attention to me" approach with the deer on the Dipper Ranch but it doesn't really work with them. Sometimes it works with the cows. I never thought about pulling up some grass stems though. Maybe that is why the cattle come over when I am chopping up thistles.


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