Double broodedness and mixed reproductive strategies by female swallows

Abstract

It has been hypothesized that female birds should alter their mixed reproductive strategy from being willing to engage in extra-pair copulations during first clutches to not being willing to do so during second clutches, because it is beneficial in terms of paternal care for females to be faithful to their mates once they have proven their quality as parents during the first clutch. Parental care for nestling and fledgling swallows, Hirundo rustica, from the first brood may overlap with the initiation of a second brood. Since male brood care interferes with the ability to mate guard, this juxtaposition may have implications for the ability of males to guard their mates during the fertile period of the second clutch. However, the intensity of mate guarding was not related to the duration of the interval between initiation of the first and the second clutch and thus the extent of brood overlap, indicating that mate guarding was not severely constrained by paternal care. The intensity of mate guarding during the presumed fertile period was as high during second as during first clutches. Accordingly, the frequency of extra-pair copulations by females was similar during first and second clutches. The magnitude of male parental investment in first versus second broods was compared. Male swallows fed first broods slightly more than second broods. Male brood defence against a human intruder was also similar for first and second broods. These data do not support the hypothesis that female swallows alter their reproductive strategy from the first to the second clutch.