Optimal foraging theory predicts that when prey density is low, predators should employ a generalist feeding strategy and take prey in proportion to their abundance. The purpose of this study was to compare the diet of common nighthawks (Chordeiles minor: Caprimulgidae) with a measure of prey abundance. Relative to the proportion of insects available, nighthawks consumed Coleoptera and Hymenoptera more than expected while Diptera were avoided. Only Trichoptera and Lepidoptera were consumed in proportion to their abundance. A qualitative comparison of our results with data on nighthawk diets from the Okanagan Valley, British Columbia, suggests that the birds in the two locations have different diets but similar preferences relative to the abundance of different insect orders.