Blackbirds Mate Choice: Dependence of Male Social Status on Age and Morphology in an Urban Population of the European Blackbird,Turdus merulaL

Adoption and feeding of fieldfare nestlings and fledglings by European blackbird

Interspecific adoption is an intriguing topic in behavioral and evolutionary ecology. As it is a rare phenomenon, seldom documented in the literature, reports of interspecific adoption based on solid data are particularly valuable. A long-term and extensive monitoring programme involving a local population of European blackbirds (Turdus merula, hereafter blackbird) has yielded, among other things, observations of alloparental behavior exhibited by blackbirds toward fieldfare (Turdus pilaris) nestlings (a single nest, the first-ever record) and fledglings (12 cases in all). We discuss the observations in the context of the available literature.

Pressure for rapid and accurate mate recognition promotes avian-perceived plumage sexual dichromatism in true thrushes (genus: Turdus)

Ecological conditions limiting the time to find a compatible mate or increasing the difficulty in doing so likely promote the evolution of traits used for species and mate recognition. In addition to interspecific character displacement signalling species identity, intraspecific traits that signal an individual's sex and breeding status reduce the challenge of identifying a compatible conspecific mate and should be more common in migratory rather than sedentary species, species with shorter breeding seasons and species breeding under high sympatry with many closely related heterospecifics. Here, we tested this recognition hypothesis for promoting plumage sexual dichromatism in the true thrushes (Turdus spp.), a large and diverse genus of passerine birds. We used receptor-noise limited models of avian vision to quantify avian-perceived chromatic and achromatic visual contrasts between male and female plumage patches and tested the influence of breeding season length, spatial distribution and sympatry with other Turdus species on plumage dichromatism. As predicted, we found that (1) true thrush species with migratory behaviour have greater plumage sexual dichromatism than non-migratory species, (2) species with longer breeding seasons have less plumage sexual dichromatism, and (3) greater numbers of Turdus thrush species breeding in sympatry is associated with more plumage sexual dichromatism. These results suggest that social recognition systems, including species and mate recognition, play a prominent role in the evolution of plumage sexual dichromatism in true thrushes.