Ecological and behavioural correlates of extra-pair mating systems: A comparison of tropical and temperate zone congeners

The frequency of extra-pair paternity varies widely among avian species, and this variation is unexplained. Few studies exist on tropical species in which great differences in ecology may provide keys to understanding correlates of extra-pair fertilization behaviour. The frequency of extra-pair paternity in a socially monogamous tropical Swallow (Tachycineta albalinea) was found to be 26% of broods (8 of 31) and 15% of offspring (15 of 97). Despite the absence of paternity assurance behaviors, Mangrove Swallows had significantly fewer extra-pair young compared to a closely related temperate zone congener, the Tree Swallows (Tachycineta bicolor). This finding could be explained by differences in breeding synchrony, and possibly breeding density. Within the population of Mangrove Swallows, however, the spatial and temporal distribution of nests with extra-pair young did not differ significantly from that of all nests. My results suggest that: (1) breeding synchrony may account for variation in EPF frequency among closely related species, but not within species, (2) breeding density does not account for variation in EPF frequency among or within species, and (3) the presence of paternity assurance behaviours do not account for variation in EPF frequency among closely related species.