Combined effects of migration distance, foraging method vegetation density, and population density on wing shapes of boreal songbirds

In birds, migration distance is known to influence morphological attributes that influence flight performance, especially wing shape. However, wing shape is under the likely influence of less documented factors such as foraging method, vegetation density and isolation of individuals and populations. To better understand factors leading to interspecific differences in wing shape, we measured the pointedness of wings (Kipps distance) of 1017 live birds of 22 species in an eastern Canadian boreal forest. We modeled wing pointedness as a function of migration distances from eBird records, foraging, habitat, and population density data from Birds of North America monographs. Long-distance migrants and species living in low-density vegetation had more pointed wings than shorter-distance migrants and dense-vegetation dwellers, in accordance to our predictions. After accounting for vegetation density and migration distance, we found no link between the extent of aerial foraging or mean breeding population density, an indicator of isolation, and wing pointedness. Those results are consistent with a tradeoff between sustained flight efficiency and maneuverability, but suggest that interspecific variation in wing shape due specifically to foraging method or habitat isolation is nonexistent or obscured by other factors.