Wing myology of Caracaras (Aves, Falconiformes): muscular features associated with flight behavior

Abstract

Caracaras (Aves, Falconiformes, Falconidae) are Neotropical diurnal raptors that belong to the subfamily Polyborinae. The forelimb myology of this group has not been comprehensively studied or compared with that of other Falconidae. Thus, the aims of this study were i) to describe the forelimb muscles of two species of Polyborinae (Caracara plancus and Milvago chimango), ii) to explore the possible relationship between muscular features and their function in flight behavior and iii) to compare the muscular features of these species with those of species of the subfamily Falconinae. To this end, the forelimb muscles of C. plancus (n=4) and M. chimango (n=4) were dissected. Additonally, to complement this data set, two specimens of M. chimachima were dissected. The mass of each muscle of one wing and its percentage with respect to the body mass were obtained. A total of 45 muscles were identified, and differences with respect to Falconinae were related to the presence of single or additional bellies. The total forelimb muscle mass represented between 7.68 and 10.26 % of the body mass. The muscle pectoralis represented ̴ 5% of the body mass, followed by the muscles scapulohumeralis caudalis (0.64–0.79%), deltoideus major (0.43 –0.53%), supracoracoideus (0.34– 0.38%) and biceps brachii (0.26 –0.39%). The high values of these muscles are in agreement with their important function: they are involved in the downstroke and upstroke phases of the flapping flight. On the other hand, the muscles that seemed to contribute little to the mechanical power for flight presented low values that ranged between 0.01 and 0.25%. Comparison of the forelimb muscles of caracaras with published data on Falconinae species suggests that their muscular features might be associated with their type of flight, which is more erratic and less powerful than that of Falconinae.