Over the course of the past century, the American bison (Bison bison) was saved from extinction and set upon a path of recovery and conservation. The Department of the Interior (DOI) has contributed significantly to bison restoration and conservation, currently managing 19 plains bison herds in 12 states, for a total of approximately 11,000 bison on 4.6 million acres of land. These DOI bison account for one-third of all plains bison managed for conservation in North America and are collectively vital to the long-term preservation of the species.
Although bison are no longer threatened by extinction, substantial work remains to restore the species to its ecological and cultural role on appropriate landscapes within its historical range. While Yellowstone bison are distinguished as the largest ecologically and genetically viable wild bison plains bison herd in North America, with approximately 4,800 bison, most DOI conservation herds have less than 1,000 individuals, are contained by fences, and are subjected to selective culling (mortality). Many herds also show some evidence of cattle gene introgression from early 19th century cross-breeding with domestic cattle. Valid concerns have been raised about how these factors and constraints may be eroding the genetic integrity and the wild character of bison that, for millennia, were shaped into resilient animals by the hands of natural selection and wide-ranging movements across large landscapes that allowed for natural dispersal and intermixing of herds.
Aiming to maximize the conservation value of DOI bison in the context of continental-wide species recovery efforts, the DOI Bison Conservation Initiative is an interagency collaboration to compile standardized, comprehensive demographic, genetic, ecological and management data of the current state of DOI bison herds to model the long-term viability of these bison herds into the future. These models, or "population viability analyses," assess the risk of extinction over time based on computational iterations that play out how a herd may expand and contract (with births and deaths) and genetically evolve given the interplay of the number, age and sex of animals in the herd; reproductive traits; influx of new genetics vs. inbreeding; management actions (culling/hunting); and potential effects of random events such as disease, drought and fire.
Outcomes from these rigorous risk assessments inform managers about how current and potential future management scenarios for both individual herds and for subsets of multiple herds that could be intermixed together (known as a "metapopulation") may affect the future generations and the conservation legacy of bison as a species. This information is central to discussions between the NPS, FWS, BLM and other stakeholders including tribes and non-government conservation organizations to developing innovative, cooperative strategies to overcome the ecological constraints of contemporary bison management that threaten the long-term viability of the species. The Initiative will also be helpful in exploring the feasibility of establishing new herds of bison that can fulfill their ecological role as a free-ranging keystone herbivore when and where appropriate on our contemporary landscapes. Ultimately, the DOI Bison Conservation Initiative is advancing our state-of-the-knowledge about our federal bison assets to develop strategic, shared stewardship partnerships within and eventually beyond the DOI to conserve the genetic diversity and wild nature of this iconic, resilient animal.