Ecological Effects of Winter Road Grooming on Bison in Yellowstone National Park

Daniel David Bjornlie

The effects of winter recreation on wildlife in Yellowstone National Park (YNP) have become high-profile issues. Snowmobiling is perhaps the most contentious of these issues. The road grooming needed to support snowmobile travel in YNP has also come under examination for its effects on bison (Bison bison) ecology. Data were collected from November 1997 through May 1998 and again from December 1998 through May 1999 on the effects of road grooming on bison in Madison-Gibbon-Firehole (MGF) area of YNP. Synoptic bison surveys of the entire study area were conducted 33 times during the study. Peak bison numbers in the study area occurred in late March/early April and were correlated with SWE measurements in the Hayden Valley area (1997-98: r² = 0.62, P < 0.001; 1998-99: r² = 0.64, P < 0.001). Data from an infrared trail monitor set up on the Mary Mountain trail between the Hayden Valley and the Firehole Valley suggest that this trail is the sole corridor for major bison distributional shifts between these locations. Of the 28,293 individual bison observations made during the study, 8% of the activities were traveling, while 69% were foraging. These percentages were nearly identical during the period of winter road grooming (7% and 68%, respectively). The majority of foraging activities during this period (77%) involved displacing snow, while 12% of the traveling activities involved displacing snow. The majority of travel took place off roads (P < 0.001). Bison utilized geothermal features, stream and riverbanks, and a network of established trails to travel in the study area. Bison road use was negatively correlated with road grooming, with the peak in April and the lowest values during the road-grooming period. Groomed road use by bison in the MGF area of YNP seems to be an activity that is neither sought out nor avoided. The minimal use of roads compared to off-road areas, the short distances traveled on the roads, the decreased use of roads during the OSV season, and the increased costs of negative interactions with OSVs suggest that roads are not the major influence on bison ecology that has been proposed.

Publication

Bjornlie, D.D., and R.A. Garrott. 2001. Effects of winter road grooming on bison in Yellowstone National Park. Journal of Wildlife Management 65:423-435.

Funding

U. S. Geological Survey and National Park Service