Bison Movement and Migration
Project Status: Ongoing
Conservation of migratory processes is an important feature of preserving the ecological role bison play in the Greater Yellowstone area. Yellowstone bison migrate during mid- to late winter, with most animals moving to the north boundary of Yellowstone National Park in February and to the west boundary in April and early May, when vegetation begins to green up on low-elevation ranges. Natural migration back into the park follows the green-up at higher elevations and typically begins on the northern range in April, and across the central range in June.
Following a study commissioned by the National Academy of Sciences in 1998, the National Park Service continued to investigate the relationship between the number of bison exiting the park, population size, and snow pack severity. Dramatic fluctuations in bison abundance and improved estimates of snow pack severity and forage productivity have provided opportunities to more precisely evaluate this relationship.
Land managers who deal with bison must understand the factors which influence movement patterns and distribution of Yellowstone bison during winter in order to effectively and adaptively manage bison on the boundary winter ranges. Bison that migrate to boundary ranges may be culled to meet brucellosis risk management obligations established in a court supervised negotiated settlement with the State of Montana. Tolerance for bison outside the park on public lands in Montana is the prerogative of the state and the Gallatin National Forest. Currently, a limited number of bison testing negative for brucellosis are allowed to use habitat north of the park boundary (except Eagle Creek) due to disease, social, and political concerns. Tolerance for bison outside the park along the west boundary is also limited in time and space as negotiated with the State of Montana.