Modeling
Bison Jump Dynamics at Bonfire Shelter
Modeling
Bison Jump Dynamics at Bonfire Shelter
If correctly interpreted as a jump site, Bonfire Shelter represents both the oldest and most southern bison jump site presently known. Bonfire Shelter in fact predates all other known jump sites by approx. 5000 years. There is no other bison jump site known in the area making Bonfire Shelter appear as somewhat of an archaeological anomaly.
Bonfire Shelter was also repeatedly used by prehistoric hunters, but its use fell at widely spaced intervals. These intervals likely coincided with certain climatic conditions which produced a grassland ecosystem amenable to subsistence of bison in the region. In both jump events, though, the notch seemed to have figured prominently. Both Bone Bed 2 and Bone Bed 3 are concentrated primarily in the talus cone directly beneath the deep crevice, know as the notch, which bisects the cliff overhang. Why was Bonfire Shelter used multiple times throughout prehistory while the rest of the region is void of archaeological evidence indicative of bison jumping? More specifically, why are both events, separated by some 7,500 years, so closely associated with the notch feature?
The unique topography of Bonfire Shelter may have offered a strategic advantage to prehistoric bison hunters. This advantage may have made the site more attractive to prehistoric hunters than any other location in the region. This may partially explain the repeated and concentrated use of Bonfire Shelter. If so, what features made Bonfire Shelter such an attractive location for bison jumping?
Derived from the literature on prehistoric bison hunting strategies, a series of conditions necessary for the successful execution of a bison jump have been identified (Frison 1979; Polk 1979; Verbicky-Todd 1984). The correct combination of these conditions may have enabled prehistoric bison hunters to successfully drive herds of bison over cliffs. Without these features, though, the task of bison jumping may have been quite difficult, if not impossible. Included in the following list are features shared by most known bison jump sites:
The presence of ideal grazing conditions or water sources in close proximity to the jump location. The bison herds must be in the general vicinity in order to successfully maneuver them to the jump-off point.
The herd must be large enough in number in order to ensure that enough momentum is gained by the moving herd. Successful jumps rely on natural bison herd dynamics. The herd follows the front runners, and if the front runners lead the herd to the cliff edge, it may be difficult to prevent the herd from going over, even if the front runners manage to escape in time.
A long, flat, and relatively straight path is needed for a drive lane. These conditions are required in order to navigate the bison to the final location without providing opportunities for escape. These conditions also permit the herd to gain enough speed and momentum.
Drive lanes are often made up of two sections. A long straight path, and a short path leading to the jump of point. This short path is at a 90 degree angle to the main drive lane. The bison are unable to see the cliff edge until they are directly upon it, giving them little opportunity to escape.
The orientation of the cliff face must be in the same direction the wind is blowing. The bison must be upwind of the cliff face. If the bison are downwind of cliff face then they will smell the hunters before they reach the jump point.
The edge of the cliff must be steep and sharp enough and the height of the cliff must be great enough to ensure that all bison go over and are at least severely maimed by the fall. There should be no chance that the bison are able to escape and scramble back up the edge and charge the hunters.
In order for Bonfire Shelter to have offered strategic advantages as a jump site over other locations in the region, all the above criteria must be met at Bonfire Shelter. It also has to be shown that other locations in the region lack the necessary criteria for a successful bison jump site. Careful analysis of the landscape topography should reveal the advantages or disadvantages of using Bonfire Shelter as a bison jump site.
This analysis has been performed using GIS tools. A high-resolution DEM of the site was created and inspected for the presence of the above criteria. Slope calculations along with the creation of least-cost pathways helped to identify potential bison drive lanes. Viewshed analyses and ArcScene camera flybys were used to simulate the perspective of the bison herd as it approached the jump off point. In combination, the results can be used to better understand how and why Bonfire Shelter was used by prehistoric bison hunters.