A control model for zygodactyl bird's foot
  In this paper we are interested to the zygodactyly phenomenon in birds, and in particolar in parrots. This arrangement, common in species living on trees, is a distribution of the foot with two toes facing forward and two back. We give a model for the foot, and thanks to the methods of iterated function system we are able to describe the reachability set. Moreover we give a necessary and sufficient condition for the grasping problem. Finally we introduce a hybrid dynamical system modeling owl's foot in various stages of hunting (flying, attack, grasp). 
Anna Chiara Lai and Paola Loreti
math.OC