Jason E. Bruggeman and Robert A. Garrott

The spatial dynamics of the central Yellowstone bison (Bison bison) herd are complex and operate at several spatial and temporal scales.  Historically, the population occupied the Pelican and Hayden grassland-sagebrush valleys of central Yellowstone and was essentially sedentary, living within these valleys year-round.  As the population recovered from near extirpation, per capita resources within these valleys became limited, forcing the population to expand its range westward and down the natural elevation gradient presented by the Nez Perce drainage.  This range expansion reestablished what appear to be traditional migratory behaviors that existed prior to the severe human exploitation that occurred in the second half of the 19^th century.  The timing and extent of the annual seasonal migrations is quite variable from year to year and is believed to be driven by a combination of population size and annual variation in climate.  Climate affects plant productivity during the growing season in the central Yellowstone valleys and snowpack dynamics during the winter period.  Understanding these interactions is essential to sound management of the bison population, as it is these mechanisms that are hypothesized to influence the propensity for animals to cross the western boundary of the Park into the Hebgen Lake Basin.  It is beyond Park boundaries where bison are subjected to highly political and controversial control actions to protect livestock from the potential of Brucellosis transmission.

The purpose of this project is to integrate data available from past research initiatives that have identified patterns of spatial distribution exhibited by bison.  Furthermore, this study is exploring in more detail how bison move across the landscape between areas of high and low occupancy of habitats and identifying the ecological drivers of these spatial dynamics.  The implications of addressing these issues are of utmost importance for managers at Yellowstone National Park, who need to understand these patterns of movement relative to bison ecology for implementing the Joint Bison Management Plan.  An insight into how and when bison are apt to move across the landscape may help predict when animals are likely to move towards, and outside of, Park boundaries where they may be subject to control actions.  In addition, understanding movement patterns will provide a mechanism for choosing locations to implement a remote vaccination program that delivers vaccines to a higher proportion of eligible individuals.  Finally, the Park needs to understand the physical distribution of the bison travel network to objectively compare how it interfaces with human travel networks—primarily the road network used by motor vehicles.  Overall, this project will provide the Park with a robust data set to educate the staff and visiting public about the ecological dynamics of bison population movements across the landscape of central Yellowstone National Park.  In addition, this study will detail the relationship between snowpack dynamics, plant phenology, and the propensity for bison to travel between foraging areas and habitats across the landscape.

Funding:  National Park Service