The masses of the locomotor and cardiac muscles of wild barnacle goose goslings, from a migratory population, were examined systematically during development and their values compared to those of pre-migratory geese. Pre-flight development was typified by approximately linear increases of body, leg, and heart ventricular mass with respect to age. Flight muscle showed an exponential increase in mass. Pectoralis muscle mass was 14.2 +/- 0.3% of body mass (1297 +/- 738, n=7) in early flying goslings compared to 16.6 +/- 0.3% of body mass (2318 +/- 109 g, n = 8) in pre-migratory geese. Post-flight development was typified by stasis of leg muscle mass but hypertrophy of ventricular and pectoralis muscle mass in proportion to body mass. Ventricular mass relative to body mass showed the lowest values at 5 weeks of age (0.62 +/- 0.01%) with peak values at 1 week of age (1.04 +/- 0.04%). The latter may be associated with both the requirements of thermoregulation in these precocial, arctic breeding geese and the need to forage approximately 24 hours post-hatch. Peak Values for leg muscle mass, relative to body mass, were found at 3 weeks of age (12.7 +/- 0.36%), with lowest values in the pre-migratory geese (6.7 +/- 0.21%), while peak values for pectoralis muscle mass were expressed in the premigratory geese with lowest values at 1 week of age (0.94 +/- 0.07%). Ventricular mass was proportional to leg muscle mass up to 5 weeks of age (M(v) = 0.38 M(t)(0.68), r(2) = 0.95), but subsequent increase in ventricular mass was proportional to pectoralis muscle mass (M(v) = 0.25M(p)(0.73), r(2) = 0.81).
