|A lone wolf surveys a bison herd at Yellowstone National Park|
|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.|
|Wolf briefly faces bison before . . .|
|. . . retreating.|
|Wolf approaching two bison bulls.|
|Wolf passing in front of bull.|
|Wolf passing to the side of two large bull bison.|
|Wolf digging next to two bison bulls.|
|Wolf surveying the bison herd again.|
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.|
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
Animal Behavior Desk Reference: A Dictionary of Animal Behavior, Ecology, and Evolution, Second Edition by Edward M. Barrows, CRC Press, 2000.