. Draft environmental impact statement for the interagency bison management plan for the state of Montana and Yellowstone National Park. American bison; American bison; American bison; Brucellosis in animals; Brucellosis in animals. Impacts on Bison Population between 1988 and 1997 showed that calves and yearlings comprised an average of 40% of total female bison killed (Pac and Frey 1991; Aune, unpub. data). Using these data, approximately 60% of the female component, or 490 bison, would be of reproductive age and capable of producing calves. Calf production for the Mary Mountain and northern
. Draft environmental impact statement for the interagency bison management plan for the state of Montana and Yellowstone National Park. American bison; American bison; American bison; Brucellosis in animals; Brucellosis in animals. Impacts on Bison Population between 1988 and 1997 showed that calves and yearlings comprised an average of 40% of total female bison killed (Pac and Frey 1991; Aune, unpub. data). Using these data, approximately 60% of the female component, or 490 bison, would be of reproductive age and capable of producing calves. Calf production for the Mary Mountain and northern range subpopulations was observed at and , respectively (Kirkpatrick et al. 1996). Using a 52% calf production value, approximately 255 calves would be born, and assuming no additional calf mortality the 1997 early winter population is estimated at approxi- mately 2,156. This number was used as a beginning population for the analysis. This number closely approximates the 1997 early winter aerial counts of approximately 2,200 Bison with nursing calf. The next step in the analysis was to construct a simple deterministic (averaging) population model that included estimates of the rate of change in the population, taking management actions into account, and estimates of changing seroprevalence rate. The rate of increase was calculated using the rate of change between the late winter population, after management removals and natural mortality, and the fall high population count for the following year (Eberhardt 1987). Early winter bison population counts and removals (Meagher, unpub. data; National Park Service and State of Montana 1996; National Park Service, unpub. data) from 1979 to 1997, when the population ranged between 1,700 and 3,500 animals, were used to calculate the rate of change for the bison population (see table 29). The geometric mean of the rate of change was calculated to be (see table 29); this means the bison population increased at an a
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