Cooperative Fish and Wildlife Research Units Program: Wyoming
Education, Research and Technical Assistance for Managing Our Natural Resources

Wyoming Project

Identifying Structure of the Yellowstone Bison Population

July 2018 - December 2022


Participating Agencies

  • NPS

The Yellowstone bison population is thought to exist in at least two separate breeding herds that use northern and central areas of Yellowstone National Park. Recent and dramatic increases in bison using northern areas and decreases in bison using central areas has raised concern that management removals have targeted the central breeding herd. Bison are managed under an Interagency Management Plan that limits population abundance and distribution. Under this plan, limited numbers of bison are allowed to migrate out of the park during winter with the remainder lethally removed when migrating beyond park boundaries. Based on counts during 2017, numbers of bison using central areas of the park may no longer be sufficient for long-term genetic conservation. However, there is some indication that the historic herd structure has broken down over time. If this is the case, with bison conforming to a single, intermixing population, then the current bison population is likely sufficiently large for long-term genetic conservation – although there are substantially fewer bison observed in central areas of the park. GPS data collected by the NPS from adult female bison during 2003-2018 will be organized and shared with the recipient. Using these data, the recipient will complete a network analysis identifying nodes representing breeding areas and winter areas and edges representing connections among breeding and wintering areas between seasons and years. The NPS will also organize and share genetic information from a subset of the individuals used in the network analysis. The recipient will assimilate the genetic information with the network analysis to describe the genetic characterization of each node. The recipient will use findings from the network and genetic analyses to analyze the susceptibility of bison based on breeding area membership and genetic composition to out-of-park management removals. This project is a collaboration of researchers across multiple agencies and includes the National Park Service, U.S. Geological Survey Wyoming Cooperative Fish and Wildlife Research Unit, and the University of Wyoming.