THE BASIS FOR FEMALE CHOICE IN AN AVIAN BROOD PARASITE

Behavioral observation and experimental manipulation of a marked population of brood parasitic brown-headed cowbirds (Molothrus ater) were conducted to determine whether or not females exhibit mate choice and to elucidate the ultimate basis for any such choice. Female choice was indicated by the fact that each female copulated with only one male, although most were courted by several. Patterns of female aggression towards males also revealed that females had the opportunity to display choice. Courtship by males was sometimes treated by females as harassment, but there was no conclusive evidence that a male provided his mate with protection from harassment by other males. Nor was there any indication of other proximate benefits or services males might have provided for females. Thus, there is no evidence that males provide females with anything other than their genes. An experimental removal of mated males and the pattern of subsequent remating of widowed females are consistent with female choice for male genetic quality.