Morphological and Ecological Predictors of Migration in Shorebirds (A Phylogenetic Perspective)

AbstractMigration is the synchronized movement of a large part of a population from breeding grounds to nonbreeding grounds driven by seasonal variation of resources and avoidance of harsh winter conditions. Migration is a central component of many species' life histories, including birds, mammals, fishes, and invertebrates. However, the interplay of ecological and evolutionary drivers of migration has long intrigued biologists and remains contentious. Shorebirds represent a valuable group for testing multiple predictors of migration, as they demonstrate a range of morphological and ecological characteristics (e.g., wing shape and habitat breadth) and a large proportion of shorebird species migrate. Here we tested whether breeding site climate, wing shape, body mass, and number of habitats occupied can predict migration across 196 shorebird species using novel Bayesian regression modeling allowing explicit decomposition of trait correlations into both phylogenetic and nonphylogenetic components. Increasing climate seasonality and pointier wing shapes favoring dispersal appeared strongly associated with migration, matching our predictions and potentially reflecting resource availability optimization and the energetic costs of migration. Higher number of habitats occupied also appeared associated with migration, perhaps reflecting selection to decrease the specific habitat requirements of migration transits. The lack of a significant relationship for body mass may reflect conflicting selection pressures, as migration efficiency (energetics) increases with body size but migration duration (and time that can be spent at breeding sites) decreases.