Muscle architecture of the hindlimb of Tyto furcata (Aves Strigiformes): Highlights in owl morphology

Abstract

The American barn owl is a nocturnal bird of prey in which hind limb movements are a key factor in obtaining food; however, the architectural properties of its hind limb muscles have not been studied. This study sought to identify functional trends in the Tyto furcata hindlimb muscles by studying muscular architecture. The architectural parameters of the selected hip, knee, ankle, and digit muscles were studied in three specimens of the Tyto furcata and joint muscular proportions with an additional dataset were calculated. Previously published information on Asio otus was used for comparison. The flexor muscles of the digits had the highest muscle mass. Regarding architectural parameters, the main flexor of the digits (flexor digitorum longus) and the muscles that extend the knee and ankle joints (femorotibialis and gastrocnemius) showed a high physiological cross‐sectional area (PCSA) and short fibers, allowing powerful digit flexion and knee and ankle extension. These mentioned features are in accordance with hunting behavior, in which prey capture is not only closely linked to the flexion of the digits but also to the movements of the ankle. During hunting, the distal hind limb is flexed and then fully extended at the moment of contact with the prey, whereas the digits are close to grasping the prey. The hip muscles showed a predominance of extensors over flexors, which were more massive, with parallel fibers and without tendons or short fibers. These features lead to a higher capacity to generate velocity to the detriment of forces, as indicated by the high values of the architectural index, their relatively low PCSA, and short or intermediate fiber length, which enhance the control of the joint positions and muscle length. Compared to Asio otus, Tyto furcata showed longer fibers; however, the relationship between fiber length and PCSA was similar for both species.

Hindlimb myology in two piscivorous raptorial birds: a quantitative comparison of the osprey and the white‐tailed sea eagle (Aves, Accipitriformes)

“…Pandion haliaetus and H. albicilla exhibit hindlimbs characterized by a substantial allocation of muscle mass to digit flexion. This pattern is in accordance with the grasping capabilities commonly observed in avian raptors (Liang et al, 2022;Mosto et al, 2013;Sustaita, 2008;Tudisca et al, 2023;Ward et al, 2002). The hip extensor and flexor muscles constitute the second most important functional group after the digit flexors.…”

“…Plot of functional space for PCSA and fibre length values for grip muscles. (a) Pandion haliaetus (this paper), Haliaeetus albicilla (taken from Mosto et al., 2021) and, other raptorial birds: Accipiter nisus , Falco tinnunculus , Asio otus and Tyto furcata (taken from Liang et al., 2022; Tudisca et al., 2023). (b) Enlargement of the box marked in A, illustrating the species Accipiter nisus , Falco tinnunculus , and Asio otus .…”

“…Hindlimbs are essential in the feeding ecology of diverse and unrelated raptorial birds (hawks, falcons, owls), as they are responsible for securing food resources. These birds can catch, transport, and kill prey using their powerful feet, which bear strongly curved claws powered by flexor muscles, capable of producing great gripping force (Backus et al., 2015; Goslow, 1972; Mosto et al., 2021; Sustaita, 2008; Sustaita & Hertel, 2010; Tudisca et al., 2023).…”