Naturally occurring populations of three species of colonial passerine birds, the Piñon Jay (Gymnorhinus cyanocephalus), Great-tailed Grackle (Quiscalis mexicanus), and Barn Swallow (Hirundo rustica), were tested for conspecific egg discrimination and the presence of intraspecific brood parasitism that such discrimination would imply. Current theory predicts that intraspecific brood parasitism, or cheating, might occur when a brood parasite's fitness is enhanced relative to a nonparasite's. Due to the high cost of parental care in altricial birds, selection for defenses against such cheaters should also be intense. Egg rejection is the most common selection mechanism against interspecific brood parasites, and I tested for the presence or absence of this mechanism. Single eggs were switched between pairs of 19 Piñon Jay nests, 15 Great-tailed Grackle nests, and 14 Barn Swallow nests, and a fifth egg was added to each of 8 Piñon Jay nests. No significant level of rejection of introduced eggs was found, possibly either because the cost of cheating is too great or because egg discrimination and rejection are not the mechanisms of selection against cheaters in the populations tested.