EXTRA-PAIR FERTILIZATIONS AND PATERNITY DEFENSE IN-HOUSE MARTINS, DELICHON URBICA

DNA fingerprinting showed that 15% of 62 house martin nestlings at stu dy colonies in central Scotland were not related to their putative fat hers, and 32% of 19 broods contained at least one extra-pair chick. Th ere was no evidence of intraspecific brood parasitism. Birds were neve r seen to mate outside nests in the vicinity of nesting colonies, and the single copulation that was observed during this study was a pair m ating that took place inside a nestbox. Extra-pair birds were often se en to enter nests, with seven of eight identified intruders being male s from other nests where laying had already taken place. Pair males ma te guarded by ensuring that females spent very little time alone at th e nest from about 7 days before the first egg of the clutch was laid, and by accompanying females on up to 70% of flights away from the nest during the 4-5 days before laying commenced. Mate guarding seemed to slacken after egg laying began, with a gradual transition to incubatio n behaviour taking place. Associated with this was a higher likelihood that the youngest nestling would be fathered by an extra-pair male. M ale removal experiments indicated that extra-pair birds were more like ly to enter the nest of a fertile female when the pair male was absent , but in three cases where DNA fingerprints were obtained male removal during the fertile period of the pair female had no apparent influenc e on paternity.