Diets of bison (Bison bison L.) were examined using microhistological
fecal analysis in a 2-yr study on a tallgrass prairie site in northcen
tral Oklahoma. Graminoids comprised at least 98% of the diet across al
l seasons. Bison showed strong feeding selectivity; grasses and sedges
formed a significantly higher proportion of diets than was generally
available in herbage on the landscape, Bison avoided forbs, which were
less than or equal to 2% of the diet, Sedges were a large (17-44 %) d
iet component in winter and spring but decreased substaintially during
summer and fall (11-16%), These changes in sedge use corresponded to
seasonal variation in sedge availability. Our results confirm that bis
on are primarily grazers in prairie habitats, potentially having a sig
nificant role in shaping structure and function of tallgrass prairie.