Extraterritorial forays are related to a male ornamental trait in the common yellowthroat

Despite numerous studies of extrapair paternity in birds, little is known about the behaviours that males and females use to seek (or avoid) extrapair copulations. We used radiotelemetry to examine the extraterritorial movements of both male and female common yellowthroats, Geothlypis trichas, in relation to male ornaments, particularly the black facial mask. We found that many males (62%) and females (47%) forayed, and they primarily visited the territories of immediate neighbours (91%). Parentage analyses revealed that the majority of extrapair sires were neighbours (80%) who typically had larger facial masks than the male that they cuckolded. Females only forayed during their fertile period, and they directed most of their forays to territories of males with larger masks than their own social mate. In contrast, males directed most of their forays to territories where the female was fertile and the resident male had a smaller mask than their own. The relatively short foray distances of birds may be partly responsible for the wide distribution of extrapair fertilizations among males in the population (45% of males). If this is a general pattern among species, then the effect of extrapair mating on sexual selection is likely to be weaker than currently thought.