Phenotypic Flexibility of Skeletal Muscles during Long-Distance Migration of Garden Warblers: Muscle Changes Are Differentially Related to Body Mass

: Mass changes of skeletal muscles occur in a variety of species during the migratory period. Phenotypic flexibility of flight muscle mass is considered to represent adaptations of the flight muscle to changing power requirements associated with changes in body mass. We analyzed the relationship between muscle masses and body mass for garden warblers (Sylvia borin) sampled during spring migration in Tanzania, Ethiopia, and Egypt, and during autumn migration in Turkey. Flight muscle mass was positively related to body mass of warblers at only one of the four sites, in Egypt where warblers had just arrived after a long migratory flight. Analysis of covariance (ANCOVA) revealed a significant interaction term between sampling site and body mass (P