Female extra-pair behaviour and environmental quality in the serin (Serinus serinus): a test of the 'constrained female hypothesis'

Recent behavioural and molecular studies have shown that in most monogamous bird species extra-pair copulations and fertilizations outside the pair bo nd occur routinely. The consequences of female extrapair behaviour might co mprise effects on important life-history traits, such as the extent of male parental care. In this study we test the assumption that, within a species , females' options for extra-pair mating depend on female quality and the e nvironments that females occupy. This 'constrained female hypothesis' predi cts that females in good environments or high-quality females are able to r esist males' control efforts better than females in poor environments or lo w-quality females. We test the idea in the socially monogamous serin. Mie f ound that the likelihood of extra-pair paternity is significantly higher in territories with high availability of food. There was a negative relations hip between environmental quality (food availability) and paternity both in natural and in experimentally manipulated habitats. Male feeding rates wer e negatively related to food availability and positively related to paterni ty. These data and the additional result that in better environments all of a females' offspring were sired by one extra-pair male provide support for Gowaty's 'constrained female hypothesis'.