Résumé
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. 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. 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 colonization. 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.