We describe the hindlimb myology of Milvago chimango. This member of the Falconidae: Polyborinae is a generalist and opportunist that can jump and run down prey on the ground, unlike Falconinae that hunt birds in flight and kill them by striking with its talons. Due to differences in the locomotion habits between the subfamilies, we hypothesized differences in their hindlimb myology. Gross dissections showed that the myology of M. chimango is concordant with that described of other falconids, except for the following differences: the m. flexor cruris medialis has one belly with a longitudinal division; the m. iliotibialis lateralis does not have a connection with the m. iliofibularis; the m. fibularis longus is strongly aponeurotic; the m. tibialis cranialis lacks an accessory tendons and the m. flexor hallucis longus has one place of origin, instead of two. The presence of the m. flexor cruris lateralis can be distinguished as it has been described absent for the Falconidae. We associated its presence with the predominant terrestrial habit of the M. chimango. Each muscle dissected was weighed and the relationship between flexors and extensors at each joint was assessed. The extensor muscles predominated in all joints in M. chimango. Among the flexors, the m. flexor hallucis longus was the heaviest, which could be related to the importance of the use of its talons to obtain food.

We studied the hindlimb myology of the monk parakeet (Myiopsitta monachus). Like all parrots, it has zygodactyl feet enabling perching, climbing, hanging, moving easily among trees, and handling food. Muscles were described and weighed, and physiological cross-sectional area (PCSA) of four flexors and one extensor was calculated. In comparison to other muscles, the M. tibialis cranialis and the M. fibularis brevis show increased development and high PCSA values, and therefore, large potential force production. Also, a large proportion of muscle mass was involved in flexing the digits. We hypothesize that these muscle traits are associated with the arboreal locomotion and food manipulation habits. In the monk parakeet, the M. extensor digitorum longus sends a branch to the hallux, and the connection between the M. flexor digitorum longus and the M. flexor hallucis longus is type I (Gadow's classification). We reaffirm the presence of the M. ambiens as a plesiomorphic condition that disappears in most members of the order. Among Psittaciformes, the M. fibularis brevis is stronger and the M. fibularis weaker in arboreal species than in basal terrestrial ones (e.g., Strigops).

The hindlimb of the Polyborinae has always been characterized as long when it was compared with other diurnal raptors; however, no empirical work has been done to support such a traditional well-known fact. The objective of this work is to analyze the femur, tibiotarsus and tarsometatarsus of this group to corroborate whether this assumption has a significant statistical support. The proportions of these bones were analyzed with a one-way Kruskal-Wallis test and Dunn's test as post hoc comparisons. The allometric relationships between the long bones and body mass or the total length of the hindlimb were carried out with the reduced major axis method. In addition, the osteological study is complemented with a myological dissection of the hindlimb of Milvago chimachima and Caracara plancus. The three long bones of the limb of Polyborinae show significant differences with those from Falconinae. The presence of a long tarsometatarsus is a typical feature of terrestrial birds, it produces an increase in length stride allowing an effective locomotion on land. Among the myological differences, the most prominent are the presence of the musculus flexor cruris lateralis (absent in other Falconidae) and a well-developed musculus fibularis longus. These osseous and myological features are related to the terrestrial locomotion present in this subfamily.

No abstract

Caracaras, falcons and forest falcons, which are representative of the three subfamilies of the family Falconidae, have different flight behaviour. Since, during flight, the tail works in coordination with the wings, the tail muscles could be indicative of the type of flight behaviour. The aim of this work was to describe in detail the littleknown tail muscles of the Falconidae and to explore their possible association with this different behaviour, by using the muscle mass as an indicator. To this end, the tail muscles of 18 specimens representing the three subfamilies of Falconidae were dissected, weighed and their percentage to the body mass calculated. The possible differences in tail muscle mass between Falconinae and Polyborinae were explored with a Bayesian statistical approach. In all species, the muscles depressor caudae and levator caudae had the highest mass values (0.028%-0.329% and 0.120%-0.274%, respectively), in accordance with the key movements performed during flight, that is, the tail depression and elevation. The total muscle masses of Falconinae and those of Polyborinae were significantly different (p < 0.05). This difference can be related with the different flight behaviour of falcons and caracaras, that is, fast and erratic flight, respectively. K E Y W O R D S diurnal raptors, locomotion | 293 MOSTO eT al.

This work is the first myological dissection performed in detail on the hindlimb of Tyto alba. Six specimens were dissected and their muscle masses were obtained. T. alba has the classical myological pattern present in other species of Strigiformes, such as a well-developed m. flexor digitorum longus and the absence of the m. plantaris, flexor cruris lateralis and ambiens. Also, T. alba lacks the m. extensor propius digiti III, m. extensor propius digiti IV and m. lumbricalis, present in the Strigidae. Hindlimb muscle mass accounts for 14.13% of total body mass, which is within the range of values of both nocturnal (Strigiformes) and diurnal (Falconidae and Accipitridae) raptors. This study provides important information for future studies related to functional morphology and ecomorphology.

Hindlimbs of raptors play an essential role in feeding due to the grasping abilities that allow them to hunt and kill their prey. This study explores and quantifies for the first time the structural and mechanical features of the digit flexor muscles in one of the largest piscivorous European raptors, the white‐tailed sea eagle. We studied the myological architecture of nine muscles of five females and five males of Haliaeetus albicilla. We found that (1) reversed sexual dimorphism was not reflected in any of these structural or mechanical variables; (2) when the physiological cross‐sectional area values of muscles were scaled altogether against body mass, they had a positive allometric tendency, implying that larger muscles have proportionally higher physiological cross‐sectional area values than smaller ones. Conversely, different scaling patterns were obtained when each flexor was analyzed individually: Only three muscles were positively allometric, and four muscles were isometric. (3) Three major groups can be identified in relation to the different features here analyzed: (1) flexor digitorum longus, flexor hallucis longus and tibialis cranialis: large muscles, with high physiological cross‐sectional area and tendon cross‐sectional area, low tendon/belly ratio and isometric; (2) flexor hallucis brevis: small muscle, with intermediate physiological cross‐sectional area and tendon cross‐sectional area, low tendon/belly ratio, short fiber length and isometric; (3) musculi perforans and perforans et perforatus: intermediate muscles, with low physiological cross‐sectional area and tendon cross‐sectional area, high tendon/belly ratio and allometric. Haliaeetus albicilla hunts mainly fish, an elusive prey, and their muscles have an anatomical design related to their common purpose, to grip prey. However, different patterns that characterize each muscle might respond to different requirements related to this particular prey item and hunting behavior and to the role each digit can perform.

Barn Owls (Tytonidae) are nocturnal raptors with the largest geographical distribution among Strigiformes. Several osteological, morphometrical, and biomechanical studies of this species were performed by previous authors. Nevertheless, the myology of forelimb and tail of the Barn Owls is virtually unknown. This study is the first detailed myological study performed on the wing and tail of the American Barn Owl (Tyto furcata). A total of 11 specimens were dissected and their morphology and muscle masses were described. Although T. furcata has the wing and tail myological pattern present in other species of Strigiformes, some peculiarities were observed including a difference in the attachment of m. pectoralis propatagialis due to the lack of the os prominence, and the presence of an osseous arch in the radius that seems to widen the anchorage area of the mm. pronator profundus, extensor longus alulae, and extensor longus digiti majoris. Furthermore, the m. biceps brachii has an unusual extra belly that flexes the forearm. The interosseous muscles have a small size and lacks ossified tendons. This feature may be indicative of a lower specialization in the elevation and flexion of the digiti majoris. Forelimb and tail muscle mass account for 10.66 and 0.24% of the total body mass, respectively. Forelimb muscle mass value is similar to the nocturnal (Strigiformes) and diurnal (Falconidae and Accipitridae) raptors, while the tail value is lower than in the diurnal raptors (Falconidae and Accipitridae). The myological differences with other birds of prey are here interpreted in association with their “parachuting” hunting style. This work complements our knowledge of the axial musculature of the American Barn owls, and provides important information for future studies related to functional morphology and ecomorphology.