Determinants of color polymorphism in the Eurasian scops owl Otus scops

Understanding the evolutionary forces maintaining avian color polymorphisms is a major challenge in evolutionary ecology. Aiming to give new insights into the functional basis of color polymorphism, we studied plumage color variation and its associations with fitness proxies in an individually marked population of scops owls (Otus scops) during 8 years. We found a repeatable method to assign individuals to three discrete morphs, using both photography and spectrophotometry. Individuals were either grey (33%), intermediate (37%) or brown (30%). Scops owl proved to be polymorphic as the three morphs were found in the two sexes and across ages. Frequency distribution of color within the population did not vary for the two sexes during the study period, and, within individuals, color was repeatable and not explained by plumage maturation. Females of the two extreme morphs seemed to mate at random while intermediate females seemed to mate assortatively. The color of females was not related t...