A Quantitative and Comparative Analysis of the Muscle Architecture of the Forelimb Myology of Diurnal Birds of Prey (Order Accipitriformes and Falconiformes)

Flight is a key feature in the evolution of birds. Wing anatomy reflects many aspects of avian biology such as flight ability. However, our knowledge of the flight musculature has many gaps still, particularly for the distal wing. Therefore, the aim of this work was to investigate the form-function relationship of the forelimb myology of birds to understand the role of individual muscles during flight. Dissections of six species of birds of prey were performed to collect numerical data of muscle architecture, which is the primary determinant of muscle function and force-generation capacity. Birds of prey are a highly diverse group that presents different flight styles throughout the taxa, making them a good model for our purposes. Wing muscle mass (MM) isometrically scaled with body mass1.035 , muscle length to MM0.343 , and fascicle length (FL) scaled allometrically to MM0.285 . The shoulder musculature scaled differently than the other regions where the FL increases more slowly than would be expected in geometrically similar animals, which affects flight mechanics. A proximal-to-distal reduction of MM occurs, which helps to minimize the wing moment of inertia during flight while allowing precise control of the distal wing. Interestingly, the distribution of MM appeared to be species-specific, suggesting a functional signal. This study provides numerical information of muscle architecture of the avian wing that helps us to understand muscle function and its implication in flight, and can be used in future studies of flight mechanics.