Differences in Fat Deposits and Wing Pointedness between Male and Female Willow Warblers Caught on Spring Migration at Ottenby, SE Sweden

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Abstract
Four major groups of Willow Warblers are distinguishable during spring migration at Ottenby, SE Sweden, South Scandinavian males (sm) and females (sf), North Scandinavian males (nm) and females (nf). Sm carry relatively more fat than both sf and nm, and nf carry more fat than sf and nm. Males have more pointed wings, but no wing shape difference was found between northern and southern populations. Morning trapping times differed between the sexes (males being caught earlier than females), in accordance with morphometric flight theory.