The primary flight muscles of the chest, shoulder, back and upper arms were weighed for 29 species of Australian bat, representing two suborders and six families. Values of muscle masses were found to be between 9 and 23% of the mass of the bat ( m bat) and aligned into three statistically distinct classes that relate foraging strategy with morphology when plotted against m bat. These classes represent 'high-energy', 'general' and 'low-energy' foraging strategies. The above relationships were visible in both the wing downstroke and upstroke muscle groups, but not in the shoulder and elbow flex/extend groups. Differences in the foraging ecologies and geographical distributions of Western Australian bats are reflected in 'flight motor power output' as well as the bats' 'airframe design' attributes. Based on these attributes and ecologies, a method is presented for estimating the mass of flight muscle.