Mixed patterns of morphological adaptation to insularity in an aerial displaying bird, the Common Snipe Gallinago gallinago

Abstract

On islands, colonizing birds may evolve behavioural and morphological adaptations to the new environment, often resulting in changes in body size and reduction or even total loss of flight. These island populations have therefore been used to test hypotheses related to adaptations for flight. However, in certain species in which flight is used not only in foraging and migration but also in mating displays, disentangling the effects of natural and social selection is difficult. Thus, sedentary populations of species that perform aerial displays (such as the Common Snipe Gallinago gallinago that breed in the Azores archipelago) may offer an opportunity to separate the effects of natural and social selection on morphology. If insular Common Snipe respond to the characteristic ecological context of oceanic islands, we expect them to differ from migratory conspecifics in body size and by having relatively smaller and more rounded wings. On the other hand, if social selection exerts a more powerful force over the morphology of this species, we expect that sedentary and migratory birds will not differ in flight‐related characters. We tested these hypotheses by comparing morphological characters measured on live Common Snipe captured in the Azores during the breeding season with those measured on migratory specimens hunted during autumn/winter in mainland Portugal. Sedentary Azorean birds were smaller and had relatively shorter tails but did not show the tendency for insular birds to possess more rounded wings as described in other taxa, including in the Azores. Bergman's rule might explain the difference in body size and shorter tails may be responsible for behavioural differences between populations. The lack of difference in wing shape might be explained by the need of the Common Snipe to perform aerial displays during courtship, suggesting an effect of social selection on the migratory strategy of this species.

Selection underlies phenotypic divergence in the insular Azores woodpigeon

“…In our analysis, this was true for both populations, and across populations, there was no difference in size in either females or males. In a previous work, Rodrigues et al (2018) found a similar case of a trait involved in social signalling not responding as predicted by insular biogeography theory: in the Azorean Common Snipe (Gallinago gallinago), wing shape did not change with loss of migratory behaviour, probably due to the use of flight displays in this species during the reproductive season.…”

Phenotypic divergence in two sibling species of shorebird: Common Snipe and Wilson’s Snipe (Charadriiformes: Scolopacidae)

“…thus social selection, on this trait (Rodrigues et al 2018). Species differences in skeleton and external measurements are small compared with those in plumage traits, suggesting that the latter diverged more rapidly.…”

“…However, a comparative study between migratory and sedentary Common Snipe found no differences in wing shape, suggesting a possible influence of display behaviour, and thus social selection, on this trait (Rodrigues et al . 2018).…”