Chapter 27 Bison Winter Road Travel. Facilitated by Road Grooming or a Manifestation of Natural Trends?

The effects of road grooming on bison (Bison bison) distribution and movements in Yellowstone National Park have been debated since the early 1990s. Meagher (1993) expressed concern that energy saved by bison traveling on packed snow, in combination with better access to foraging habitat, resulted in enhanced population growth and increased movements to boundary areas. Thus, she recommended prohibiting road grooming to reduce the number and rate of bison leaving the park and induce them to revert to their traditional (i.e., pre-road grooming) distributions (Meagher 2003). Conversely, Bjornlie and Garrott (2001) suggested that grooming of roads during winter did not have a major influence on bison ecology because of minimal use of roads for travel (19%) compared to off-road areas, decreased use of roads during the grooming season, and short distances traveled on roads. In 2003, the U.S. District Court for the District of Columbia rebuked the National Park Service for not identifying which argument it found persuasive and instructed the agency to gather necessary data to make a reasoned choice (294 F. Supp. 2d 92, 115). To aid in this decision, we documented (1) spatial patterns in bison road travel, (2) landscape attributes affecting these trends, and (3) abiotic and biotic factors influencing temporal variability in travel on and off roads during November-May from 1996-1997 through 2005-2006 to evaluate if trends in road travel were facilitated by road grooming or a manifestation of general bison travel patterns throughout the landscape.