The Ecology of Bison Movement and Distribution in and Beyond Yellowstone National Park: A Critical Review with Implications for Winter Use and Transboundary Population Management

Gates, C.; Stelfox, Brad; Muhly, Tyler; Chowns, Tom; Hudson, Robert

INTRODUCTION Prehistorically, Yellowstone National Park (YNP) bison ranges were probably linked by migration to expansive grasslands surrounding the Yellowstone Plateau, particularly the Northern Range. Historical accounts indicate that interior ranges also supported resident bison. Market and subsistence hunting extirpated bison from the Greater Yellowstone Area by the late 1800s, except for a small remnant population in the remote interior of the park. Eventually, legislation and enforcement provided protection allowing the population to increase slowly. Bison from Montana and Texas were imported to restore the species to the Northern Range of the park in 1902, which together with the wild herd formed the foundation stock for the present day population. Intensive management limited the size of the population until the mid-1960s when a policy change of ‘ecological management’1 allowed large mammal populations in the park to self regulate in relation to ecological conditions. This form of management has been popularly referred to by the confusing term ‘natural regulation’. As the bison population increased, their range expanded, resulting in increasing numbers moving to contiguous habitat on the western and northern boundaries of the park. The YNP bison population carries the pathogenic bacterium Brucella abortus, which is infectious to cattle and people causing the disease brucellosis. Originating with cattle, the organism has been the subject of a national eradication program spanning 70 years and costing an estimated $3.5 billion in public and private funds. Fearful of the risk of transmission of brucellosis from wild bison to cattle, federal and state agencies negotiated the management of bison moving from the park into Montana at West Yellowstone and near Gardiner. Management actions have included hunting, culling by government personnel, capture and slaughter and hazing bison back into the Park. All have been controversial, especially when the combination of a large population and severe winter conditions induce migration of significant numbers of animals to the Montana boundaries where large removals have occurred. In one particularly harsh winter in 1996-1997, more than 1,000 bison were removed from the boundary ranges.