Polyandry in the mating system of the American Goldfinch, Carduelis tristis

Abstract

For the first time, regular and recurring classical polyandry is documented in a passerine species, the American Goldfinch. Between 1979 and 1985, five cases of polyandry were documented through observations at the nests of colour-banded birds. Based on the timing of second broods combined with a change of mates, an additional seven cases of polyandry were suspected to have occurred between 1969 and 1978. Polyandry was attempted by females with previous breeding experience and provided a successful strategy for producing a second brood in a short breeding season. The fledging success of known polyandrous females was 7.4 ± 0.81 young per season compared with 2.3 ± 0.22 for nests of all other females. Polyandry occurred at a minimum of 4.9% of all nests at Guelph.