Functional morphology of the hindlimb musculature of the black-billed magpie, Pica pica (Aves, Corvidae)

Abstract

 In spite of the ecological relevance of terrestrial locomotion for many bird species, this function remains poorly studied to date. Gait preferences and transitions seem present, but it is not known which factors might determine the running style. Morphological and morphometric data needed for further biomechanical modelling are presented for the black-billed magpie (Pica pica), a species which walks, runs and hops. Detailed descriptions of the muscle–tendon systems and the attachment sites on the hindlimb skeleton are given. Pinnation angles, fibre lengths and muscle masses are determined. From the latter two, physiological cross-sections of the muscle bundles are calculated. Tendon ossifications are qualitatively scored. Further, information on the mechanical variables of the body segments are collected (i.e. mass, length, position of the centre of gravity and moment of inertia of digits, tarsometatarsus, lower leg, upper leg, body, and head/neck). Moment arms of the important muscles powering terrestrial locomotion are discussed and, for some upper leg muscles, an equation to calculate the moment arms as a function of knee and hip joint angles is presented. All these data are indispensable for further kinesiological research.