The ability of an animal to localize sound is correlated with its ethological niche. Birds face a particularly difficult task in sound localization, since they must localize well in both azimuth and elevation: The azimuth of a target is of no use to an airborne predator unless it can also determine the target's elevation. Furthermore birds must perform sound localization with access to only a limited range of low sound frequencies (<12 kHz), with heads that provide little sound shadow, and with ears that have no pinnae and are close together. However behavioral, physiological, and anatomical data suggest that the auditory systems of birds are capable of extremely fine time resolution. Also, birds have elaborated a large, patent air canal connecting their two middle ears that might improve the directional properties of their ears. Finally, some birds have developed asymmetrical ears that cause interaural time and interaural intensity cues to assume different axes of symmetry. It is proposed that these adaptations permit birds to achieve a high level of sound localization ability, the best of which rivals, and may exceed that of man. [Work supported by NIH.]