Mate choice in Darwin's Finches

Female Geospiza conirostris on Isla Genovesa, Galapagos, pair preferentially with males who have had previous breeding experience. They choose mates on the basis of courtship behaviour and black adult plumage. By mating with experienced black males, they gain a fitness advantage in terms of fledgling production and recruitment of young into the breeding population. Behavioural signs of past breeding experience and black plumage are reliable age- and condition-dependent traits. We suggest that females use conspicuous black plumage to identify old males at a distance, then interactions through courtship to modify initial assessments. Females paired with inferior males may increase the genetic quality of their offspring by extra-pair copulations; results of heritability analysis of morphology are consistent with this suggestion. Females change mates at a frequency of 12–27% per breeding season. They re-pair with males who are generally old, experienced, and hold territories adjacent to the deserted male. Females that re-pair gain a benefit, whereas males who are deserted within a breeding season incur a cost of more than 50% of their future potential production for that season. We conclude that females in choosing males seek reliable indicators of potential parental care, and in addition they may seek indicators of genetic quality.