The white-tailed hawk (Buteo albicaudatus) formerly nested in the American Southwest but no longer appears to do so. We hypothesize that the reason for the absence of this always-scarce species in Arizona and Sonora, Mexico, is the elimination of its grassland habitat caused by cessation of grass fires in the tropic-subtropic regions of these two states. Loss of subtropical grasslands in the Southwest was due to livestock grazing removing fine fuels for grassland fires. When grassland prey sources became scarce due to the reduction in grass cover, nutritional levels were no longer sufficient to allow the white-tailed hawk to successfully engage in nest-building, egg-laying and the rearing of young. These conditions, initiated in the 1880s, have continued through to the present day in both southern Arizona and Sonora.