Weather conditions affect levels of extra‐pair paternity in the reed buntingEmberiza schoeniclus

Abstract

Extra‐pair paternity (EPP) is common in many socially monogamous birds, but large variations in frequency of EPP are found both between and within species. Local ecological factors can affect the costs and benefits of extra‐pair mating behaviour, and may therefore influence the chance that individuals engage in extra‐pair copulations (EPCs). We investigated the effect of weather conditions during the peak fertile period of the female on the levels of EPP in reed buntingsEmberiza schoeniclus. The reed bunting is a socially monogamous passerine, with extremely high levels of EPP (50% of offspring in 80% of broods). We found that higher daily minimum temperatures and more rainfall during the peak fertile period were associated with lower proportions of EPP. As during adverse weather conditions individuals have to invest more in self maintenance, we suggest that during long periods of rain the extra‐pair mating behaviour of all individuals will be restricted, leading to lower proportions of EPP. During cold mornings, time‐consuming activities such as mate guarding are likely to be more strongly affected than less time‐consuming activities such as EPCs, leading to higher proportions of EPP.