Strict monogamy in a semi-colonial passerine: the Jackdaw Corvus monedula

In this study we used DNA fingerprinting to provide an accurate measure of paternity in a nest-box colony of Jackdaws. The species is a semi-colonial, socially monogamous passerine which establishes long-term pair bonds. Parents raise a single annual brood in which 50% brood reduction is commonplace. However, nest sites are a limited resource, non-breeding adults are also common around colonies and males are frequently separated from their incubating females during the fertile egg-laying period so that opportunities arise for extra-pair copulation. The parentage analysis, however, revealed no cases of extra-pair fertilisation (EPF) or intra-specific brood parasitism. Therefore fledgling output or survival is likely to be a good measure of individual reproductive success in this species. The lack of EPFs is not explained by nesting synchrony and we discuss the relative costs and benefits to females of seeking EPFs; the likelihood that paternal care and a life-history strategy similar to many long-lived non-passerines may also constrain the species to monogamy.