APA Dictionary of Psychology

in socially monogamous species, mating that occurs with individuals other than the mate. In many monogamous bird species, genetic evidence of paternity suggests extensive extrapair mating, with the result that many chicks are not sired by the male that cares for them. Extrapair mating might also occur at times when conception is not possible, either to test other potential mates or to strengthen social relationships with others. See also cuckoldry.