Meeting Abstract
Birds use their feet for a large range of functions including grasping behaviors. Many perching, raptorial, and vertically clinging birds show shortened proximal phalanges in their feet. To test the relationship between grasping behavior and phalangeal proportions, we conducted Bayesian phylogenetic comparative analysis on about 200 bird species using phylogenetic ANCOVA and compared alternative models using a Bayesian Information Criterion to select the most-fitting model while penalizing by the number of additional parameters. The most well-supported model in our analysis finds that the lengths of proximal phalanges in raptors are significantly shorter than other birds, suggesting extreme grasping strength in birds is related to shortened proximal phalanges. We then investigated the biomechanical mechanism for this phenomenon. The flexor complex of the avian foot acts as a series of complex pulleys and levers. Theoretical modeling of this system predicts the reduction in phalangeal length increases the mechanical advantage of each phalange, but to test this principle in such a complex system, we designed a series of physical models created from CT-scanned and 3D printed bird feet rearticulated into biomimetic robotic models. These models confirm that proximal phalangeal shortening does not directly increase the pressure exerted by the talons, it instead increases the pressure exerted by the interdigital pads. Our models showed that a 50% decrease in phalangeal length increases the interdigital pressure by over 160% with the same muscular effort. This suggests shortenings proximal phalanges increases the strength of the core of the foot rather than the pressure exerted by the tips of the talons.
