Extrapair mating system of an asynchronously breeding tropical songbird: The Mangrove Swallow

Variation in the extent of extrapair paternity among avian species could re sult from ecological differences in breeding synchrony and/or density or th e existence or absence of paternity guards. We studied the extrapair mating system and paternity-assurance behaviors of an asynchronously breeding tro pical songbird, the Mangrove Swallow (Tachycineta albilinea), and compared this species with the synchronously breeding temperate zone Tree Swallow (T achycineta bicolor). Mangrove Swallows had a moderate level of extrapair pa ternity (26% of broods, 15% of nestlings), low breeding synchrony (8% of fe males fertile simultaneously), and low breeding density (average nearest-ne ighbor distance 313 m). The spatial and temporal distribution of nests with and without extrapair young did not differ significantly. Males did not fo llow their mates closely during the female's fertile period, and within-pai r copulation frequency was low (0.33 copulations/h). Mangrove Swallows had a significantly lower proportion of extrapair young compared with Tree Swal lows. Differences in breeding synchrony may explain the difference in extra pair paternity between the two congeners.