Inter-specific and intra-specific variability in fruit color preference in two species of Turdus.

One of the main hypotheses proposed to explain the evolution of fruit color deals with a preference of avian frugivores for specific colors, mainly black and red, which are the most common fruit colors in many of the studied habitats. I analyzed fruit color preferences by wild birds belonging to 2 species of the highly frugivorous genus Turdus (Eurasian Blackbird Turdus merula Linnaeus, 1758 and Redwing Turdus iliacus Linnaeus, 1758) by means of captivity experiments with artificial fruits. Despite important within-individual (i.e. temporal) and among-individual variability, consistent patterns of species-specific color preferences emerged. Eurasian Blackbirds tended to prefer red over blue, green and black, whereas Redwings seemed to prefer black over the rest. Green was systematically avoided by both species, suggesting that it might signal unripeness of fruits. Both preferred colors have been previously reported as the most common among fleshy-fruited plants. The high variability, both within and between individuals, in preferences suggests that they can be subject to changes through experience and learning and, therefore, are not likely to drive the evolution of fruit color. The main differences between both species could be related to the most common fruit color they fed upon during the last months before capture.