Spring migration decisions in relation to weather are predicted by wing morphology among trans-Mediterranean migratory birds

Abstract

Summary: 1. Meteorological conditions are critical determinants of bird migration. However, response to weather should vary among species as well as between males and females, as phenotypic traits relevant to migration are also shaped by natural selection acting differentially on species and either sex in other life cycle phases. 2. We studied the covariation between capture frequencies and meteorological conditions at departure and at a stopover site during northward spring migration in 21 species of migratory birds. The stopover site is a small island located at the northern end of a wide ecological barrier (the Mediterranen Sea), that is crossed with non-stop flights by migrants departing from North Africa. 3. Head and crosswinds at departure, and tail and crosswinds at stopover reduced the number of birds captured, although the strength of these effects varied among species. In the subset of 10 sexually dimorphic species, males and females were not differentially susceptible to weather conditions. 4. Because sexual and natural selection pressures on traits relevant to migration vary among species, we investigated whether body mass and wing morphology predicted species susceptibility to weather in analyses controlling for phylogenetic effects, using wing loading, wing aspect ratio, the 'brachial index', and wingtip roundedness and convexity as indicators of the morphology of the flight apparatus. 5. Captures of species whose wing morphology is more typical of long-distance migrants were less affected by tail and crosswinds, suggesting that long-distance migrants are less susceptible to weather. 6. Meteorological conditions at departure independently concurred with those at stopover in determining capture frequencies. The effect of weather on migration covaried with wing morphological traits that co-evolved with migratory strategies. Changes in meteorological conditions driven by current climate change thus have the potential to differentially affect migration phenology in relation to migratory strategy and morphology of individual species. © 2009 The Authors. Journal compilation © 2009 British Ecological Society.