Extrapair Mating System of an Asynchronously Breeding Tropical Songbird: The Mangrove Swallow

Variation in the extent of extrapair paternity among avian species could result from ecological differences in breeding synchrony and/or density, or the existence or absence of paternity guards. We studied the extrapair mating system and paternity-assurance behaviors of an asynchronously breeding tropical songbird, the Mangrove Swallow (Tachy-cineta albilinea), and compared this species with the synchronously breeding temperate zone Tree Swallow (Tachycineta bicolor). Mangrove Swallows had a moderate level of extrapair paternity (26% of broods, 15% of nestlings), low breeding synchrony (8% of females fertile simultaneously), and low breeding density (average nearest-neighbor distance 313 m). The spatial and temporal distribution of nests with and without extrapair young did not differ significantly. Males did not follow their mates closely during the female's fertile period, and within-pair copulation frequency was low (0.33 copulations/h). Mangrove Swallows had a significantly lower proportion of extrapair young compared with Tree Swallows. Differences in breeding synchrony may explain the difference in extrapair paternity between the two congeners.