The risk of brood parasitism does not affect levels of extrapair paternity in a cuckoo host

Abstract In socially monogamous bird species, extrapair paternity is common, but its level varies considerably within and among species. For hosts of brood parasites, the risk of brood parasitism may influence the costs of engaging in extrapair copulations (e.g., leaving the nest undefended) and the benefits of having extrapair young (e.g., spreading the risk of nest predation). However, whether brood parasitism risk affects extrapair behavior in host species has rarely been tested. We investigated whether variation in the risk of brood parasitism affected levels of extrapair paternity in Daurian redstarts, a socially monogamous passerine. As a common host of the common cuckoo, the redstart is unique in that its first clutch of the year takes place before the arrival of cuckoos. As a consequence, redstarts experience large seasonal variation in cuckoo parasitism risk, with no parasitism in the first egg-laying period and a high risk in the second period. We genotyped 995 nestlings (and unhatched eggs) from 181 broods and found moderate levels of extrapair paternity, with 34.8% of broods containing at least one extrapair young and 11.7% of all offspring being sired by an extrapair male. However, levels of extrapair paternity did not differ between the first and the second egg-laying period. Also, experimentally simulating parasitism risk during the first egg-laying period by broadcasting cuckoo vocalizations and presenting taxidermic models of cuckoos did not affect levels of extrapair paternity in redstarts. Our results, therefore, suggest that the risk of brood parasitism does not affect host extrapair paternity.