Adaptations of the Gray Catbird Dumetella carolinensis to Long-Distance Migration: Flight Muscle Hypertrophy Associated with Elevated Body Mass

Abstract

The size and composition (lean-dry, water, and fat contents) of the flight muscles of the catbird were investigated as a function of the large seasonal changes in body mass which occur in this species. The mass of the pectoralis muscle is highly positively correlated with body mass, leading to an elevation in muscle mass of ∼35% during fall premigratory fattening. The changes in muscle mass are brought about by coordinated variations in all major components of the muscles which were measured. High-oxidative, fast-twitch fibers represent 88% of the total fibers in the pectoralis muscle. The cross-sectional area of the muscle fibers increases proportional to muscle mass, suggesting that fiber hypertrophy may underlie the changes in muscle mass. Calculations of the power available from the muscles compared with the aerodynamic power required by catbirds in flight indicates that augmentation of pectoralis muscle mass could make a significant contribution to flight performance.