Mate acquisition in the European blackbird and its implications for sexualstrategies

Female European blackbirds, Turdus merula have been shown to engage in mixe d reproductive strategies and females do not seem to gain any material bene fit from their extra-pair copulation behaviour. To test the hypothesis that such behaviour arises out of constraint on their choice of social mate, I investigate if and how these females are constrained in their choice at mat e acquisition. I recorded patterns of territorial distribution and interact ions between resident birds both before pairing and during the breeding sea son. Patterns of observed behaviour agreed with earlier descriptions of win ter and breeding territoriality and provided clues to the underlying mechan ism of mate acquisition. I conclude that the constraint on breeding success imposed by high nest predation promotes intrasexual competition for high q uality nesting habitat between females prior to pair formation. Female dist ribution promotes intrasexual competition between males for territorial are a overlapping females or for habitat likely to be occupied by females. Mate choice during pair formation is constrained by the outcome of this intrase xual competition and, typically, overlapping territorial males and females pair into social monogamy on a shared breeding territory Although this ulti mately leads to assortitive mating by competitive ability, low quality fema les paired to low quality males may improve upon the quality of their genet ic mate by engaging in extra-pair copulations. These data suggest that the process Of mate acquisition in urban European blackbirds constrains the cho ice of social mate and so generates sexual selection pressures to drive mix ed reproductive strategies during the breeding season.