Sperm competition in the zebra finch, Taeniopygia guttata

Abstract

Extra-pair copulation is known to occur in zebra finches in the wild and the aim of this study was to examine several aspects of sperm competition in domesticated zebra finches breeding in captivity. Female zebra finches are fertile between day −11 and +3 (where day 0=the day the first egg is laid). Pair copulation occurs about 12 times per clutch, peaking on day −1 and decreasing markedly after day 0. Copulation was most frequent in the first hour of the morning. Copulation behaviour of zebra finches breeding in groups in an aviary differed from that of single pairs in cages in that copulations were often disrupted in the aviary, and multiple pair copulations occurred in the aviary but not in cages. Extra-pair courtship was common in the aviary and extra-pair copulation was observed. All extra-pair copulations occurred within the female's fertile period. Males guarded their partners by close following, defended them from extra-pair copulation attempts, and sometimes followed extra-pair copulations by forced pair copulations. The temporary removal of guarding males greatly increased the likelihood of the female being subject to extra-pair copulation attempts. Genetic plumage markers were used to determine paternity, and showed that in an aviary, naturally occurring extra-pair copulations resulted in extra-pair paternity. Sperm competition experiments showed that single extra-pair copulations could fertilize eggs and that sperm from the last male to mate had 70–80% precedence over previous matings.