Bison Weights from National Parks in the Northern Great Plains

On the Ground Female bison at three Northern Great Plains parks reached maximum size at 5.5 years of age. Male bison reached maximum size around 10.5 years of age. The mean weight for females 5.5 years old and older was 473 kg, and for males 10.5 years old and older was 816 kg. The mean weight for yearling females was 307 kg, and for yearling males was 325 kg. There were significant differences in bison weights between the three parks even though the herds were all stocked well below the forage-based carrying capacity. Heavier calves and yearlings tended to be heavier adults; however, there was much variability among individuals. Accurate and unambiguous data on bison weights can be used to set stocking rates and make other management decisions and therefore should be collected whenever possible.