Mechanical analysis of avian feet: multiarticular muscles in grasping and perching

Abstract

The grasping capability of birds' feet is a hallmark of their evolution, but the mechanics of avian foot function are not well understood. Two evolutionary trends that contribute to the mechanical complexity of the avian foot are the variation in the relative lengths of the phalanges and the subdivision and variation of the digital flexor musculature observed among taxa. We modelled the grasping behaviour of a simplified bird foot in response to the downward and upward forces imparted by carrying and perching tasks, respectively. Specifically, we compared the performance of various foot geometries performing these tasks when actuated by distally inserted flexors only, versus by both distally inserted and proximally inserted flexors. Our analysis demonstrates that most species possess relative phalanx lengths that are conducive to grasps actuated only by a single distally inserted tendon per digit. Furthermore, proximally inserted flexors are often required during perching, but the distally inserted flexors are sufficient when grasping and carrying objects. These results are reflected in differences in the relative development of proximally and distally inserted digital flexor musculature among ‘perching’ and ‘grasping’ taxa. Thus, our results shed light on the relative roles of variation in phalanx length and digit flexor muscle distribution in an integrative, mechanical context.

The Hindlimb Myology ofTyto alba(Tytonidae, Strigiformes, Aves)

“…There are several studies considering the muscles and bones under a biomechanical perspective (i.e. Goslow, 1967;Ward et al, 2002;Einoder and Richardson, 2006;Backus et al, 2015). There are studies where the focus is a descriptive myology of the Owls, but they are not as many and, in those cases, the family considered is Strigidae and not Tytonidae (Garrod, 1873;Garrod, 1874;Hudson, 1937;Volkov, 2004).…”

Foot shape in arboreal birds: two morphological patterns for the same pincer‐like tool

“…Humans, being primates, belong to an essentially arboreal clade, but the foot has become secondarily specialized to bipedal terrestrial locomotion. Birds originate from bipedal, terrestrial, and cursorial theropods, and the adaptation for perching comprises modifications of the proportions of the feet (Hopson, 2001;Kavanagh et al 2013;Backus et al 2015) and a new orientation of the toes (Bock & Milner, 1959;see Sustaita et al 2013 for a review). By analyzing the morphology of the foot in perching birds, our aim was to identify the characteristics of this specialization in birds.…”

“…A modification of the orientation of the toes is observed in most arboreal clades. To grasp efficiently, the foot needs to be able to exert two opposing forces on the branch and hold it in a vice-like grip (Backus et al 2015). Depending on their orientation, the toes will participate in one or the other part of the vice and the mechanical demands on the toes will thus be different.…”

Design and Fabrication of Robotic Gripper

“…Backus et al (2015) studied a grasping behavior of a simplified bird foot in response to the downward and upward forces imparted by carrying and perching tasks, respectively. They explicitly, compared the performance of various foot geometries in performing these tasks when only actuated by distally inserted flexors, for both distally and proximally inserted flexors [10].…”

“…Feix et al (2015) presented a kinematic model of thumbindex precision grip and manipulative movement based on bony hand morphology in a broad sample of extant primates and fossil hominins [9]. Backus et al (2015) studied a grasping behavior of a simplified bird foot in response to the downward and upward forces imparted by carrying and perching tasks, respectively. They explicitly, compared the performance of various foot geometries in performing these tasks when only actuated by distally inserted flexors, for both distally and proximally inserted flexors [10].…”