Intraspecific variation in the wing shape of the long-distance migrant Reed Warbler Acrocephalus scirpaceus:: Effects of age and distance of migration

Intraspecific variation in the wing shape of the long-distance migrant Reed Warbler Acrocephalus scirpaceus: effects of age and distance of migration, The wing morphology of Reed Warblers Acrocephalus scirpaceus was studied during the breeding and non-breeding cycle in a western Mediterranean area. Wing morphology was first analysed by means of a principal component analysis (PCA) on primary lengths, which corrects for allometric effects on wing shape. Two-way ANOVAs were then used to test for differences in wing morphology according to age, month and their interaction. The PCA produced two components that were related to flight-related traits, namely wing convexity and wing-tip roundness. Primary feather wear was the factor that produced most differences between ages, since adults had a more convex and rounded wing than juveniles at the outermost edge of the wing. Monthly differences in wing shape appear to indicate that differential time of migration among morphologically distinct ages could have accounted for temporal variation in wing shape, pointing that adults increased the wing components during migratory passages while juveniles showed little variation. The existence of a morphological trade-off between costs of manoeuvrability and costs of migration is discussed in order to explain differences in wing shape between ages. Key words: Acrocephalus scirpaceus, age classes, migratory waves, PCA analysis, wing shape.