10At present, studies of reinforcement should be focused on demonstrating how often this process occurs in nature and how important it is for speciation. Here we study the character displacement within the breeding area in the Pied Flycatcher to check the validity of the reinforcement in Ficedula flycatchers. We used point-referenced spatial data and a random forest to find the most important explanatory factors of the character 15 displacement, and to reconstruct the phenotypic structure of the populations. The environmental temperature, and not the distance to sympatry, were proven to better describe the geographic pattern of the mean breeding plumage colour of the Pied Flycatcher populations. We conclude that ecologically distinct adaptations drive the morphological differentiation of the Old World flycatchers, and not reinforcement. 20