The Brown-headed Cowbird (Molothrus ater has long been
associated with bison (Bos bison) in North America on the Great
Plains (Friedmann 1929). As a result, I anticipated that
cowbirds would parasitize host nests more frequently in the
presence of bison than in their absence. I predicted that
several common ground-nesting avian species, Dickcissels (Spiza
americana), Grasshopper Sparrows (Ammodramus savannarum), and
Eastern Meadowlarks (Sturnella magna), would suffer higher
frequencies of brood parasitism in bison-grazed habitat than in
ungrazed habitat on the tallgrass Konza Prairie Research Natural
Area, located in northeastern Kansas. The frequency of cowbird
parasitism for all species combined was significantly higher in
bison-grazed (0.69) than in ungrazed habitat (0.44) (p =0.044,
X2 = 4.061, df =1). These results are consistent with the
hypothesis and suggestion that bison-grazed habitat may be a
more optimal site for cowbird brood parasitism than ungrazed
habitat. I pose two principal explanations for