The importance of hybridism to ornithology has been debated. Certain hybrid combinations have critical implications to species conservation, for example, the swamping of the American Black Duck (Anas rubripes) and Hawaiian Duck (A. wyvilliana) by introgression with the Mallard (A. platyrhynchos). Others add insight to taxonomy and evolutionary biology, for example, contact among several closely related pairs of passerine species that have recently bridged the Great Plains. Whereas these and other cases of widespread hybridism are well studied, most avian hybrids seemingly have been produced by chance encounters, best viewed as anomalies. For the field ornithologist, such chance hybrids are at least an enlightening source of entertainment and may provoke in-depth discussions on species identification, plumage, vocalizations, molt, breeding behavior, and other aspects of avian natural history.