Great Basin Naturalist


The historic range of the bison (Bison bison) on the Great Plains has been well documented. In Colorado the range of bison included both the eastern grasslands and higher-elevation ridges and mountain parks, up to an elevation of 3900 m. Based on the commensal relationship of the brood-parasitic Brown-headed Cowbird (Molothrus ater) with the bison, we suggest that the cowbird had a larger historical elevational range in Colorado than previously known and consequently has had a long-term host-parasite relationship with high-elevation breeding songbirds.