Reproductive advantages of multiple female ornaments in the Asian Barn Swallow Hirundo rustica gutturalis

Recent research has increasingly focused on female ornamentation, with several studies having investigated female ornaments in relation to reproduction. However, most previous studies have focused on single female ornaments, while females of numerous species, particularly birds, possess multiple ornaments. It is still unclear whether multiple female ornaments are linked to reproductive performance, though this information is crucial for understanding how these ornaments have been maintained. In this study, we examined the signaling function of multiple female ornaments in the Asian Barn Swallow Hirundo rustica gutturalis in Japan. First, females with previous breeding experience in the study population had longer tails and more colorful throat patches than other females. This indicates that these ornaments can provide information about the breeding experience of females to conspecifics. In contrast to males, the size of white tail spots was not significantly related to breeding experience in females, partly because females with larger white spots were less likely to return to breed after a failed clutch. Second, females with longer tails and more colorful throats started breeding earlier than others, even after controlling for confounding factors, and they paired with attractive males (thereby obtaining their direct and indirect benefits too), suggesting a mating advantage for females with such ornaments. In addition, males paired with long-tailed females invested more in paternal care. These observed patterns differed from those of males, for whom the throat coloration and the size of white tail spots, rather than tail length, were significant predictors. In fact, a sex-combined analysis of breeding date demonstrated significant interactions of sex in relation to tail length and the size of white tail spots, indicating differential selection between the sexes. Our data suggest that selection on females may facilitate the evolution and maintenance of some female ornaments, partially independently of male ornaments.