Sperm competition in the chaffinch: the role of the female

Abstract

Abstract. Studies of sperm competition in birds need to consider the extent to which female choice acts in addition to intra-male competition. With this aim, the reproductive behaviour of a colour-marked population of chaffinches, Fringilla coelebs, was studied in relation to the time of the female nesting cycle. The male of the pair was responsible for maintaining pair proximity, and the female increased the rate at which she moved away from her mate as she got closer to egg laying, thus apparently not cooperating with the male's mate guarding. Females had a very distinctive and frequent copulation solicitation display that they performed for up to 15% of their time, peaking 3-5 days before the first egg was laid. Although pairs copulated at a very high rate (peaking at 4·35 copulations/h), fewer than half of the female solicitations were followed by a copulation. Males frequently intruded onto the territories of other pairs, and sometimes achieved extra-pair copulations with females there (14 cases observed); however, females also sometimes sought extra-pair copulations from males on other territories (six cases observed). Males intruded into a territory more often just after the resident female had solicited a copulation, and females solicited extra-pair copulations closer to egg laying than they did pair copulations. It is argued that by performing a conspicuous solicitation display females are in effect signalling their fertility to neighbouring males, and that other behaviour that they perform is consistent with their using the increased level of male-male competition, and their control of copulation behaviour, to choose potential fathers for their offspring.