Morphological Evolution in Island Birds Is Associated With More Terrestrial Lifestyles and a Lower Number of Raptors and Intra‐Family Competitors

ABSTRACT Aim Island biotas experience unique ecological conditions, such as isolation, small areas, or simplified communities that promote repeated patterns of evolution like changes in body size, that have been widely studied. By contrast, apart from the evolution of flightlessness in birds, changes in body shape remain relatively less explored. Here, we explore the effect of insularity on the evolution of locomotion‐related traits. Location Global. Time Period Current. Major Taxa Studied Birds. Methods We used 796 pairs of endemic island birds and their closest mainland relatives (1170 species total) to explore the effect of insularity on the evolution of locomotion‐related traits, specifically wing shape and length, and tarsus length. Furthermore, we assessed the effect of the number of raptors and intra‐family competitors (as the co‐occurring species belonging to the same family) on these patterns. Results We found that endemic island birds evolved features adapted to a more terrestrial mode of locomotion, characterised by rounder wings and longer tarsi compared to their mainland counterparts, while we did not observe a reduction in wing length. A lower number of raptors and intra‐family competitors on islands was associated with shorter tarsi, especially in passerines. Wing shape was also affected by the loss of migratory behaviour after island colonisation. Main Conclusions Our results show a general pattern of morphological evolution in island birds that favours a more terrestrial lifestyle, likely accentuated by the absence of predators and reduced competition.