LONG HINDLIMBS CONTRIBUTE TO AIR-RIGHTING PERFORMANCE IN FALLING TREE FROGS

Abstract

Tree frogs are able to climb or even jump on leaves and branches using their toe pads adhering to and detaching from surfaces, but have to be in the face of the risk of falling down due to fatigue or a slip. While falling down from a great height, air-righting response was observed, which prevents tree frogs from injury caused by back hitting the ground, however the mechanism underlying is unknown. Using a high-speed camera with a plane mirror, we captured the body and limb kinematics of falling tree frogs as they performed rapid air-righting response in three-dimension. The kinematics were then characterized into three stages and substituted into a mathematical multi-body model to simulate the air-righting dynamics caused by the kinematics. The results show that a head-down tree frog performs rapid air-righting with specific series of actions in hindlimb motion, which generates sufficient local angular momentum for the frog to rotate its body upright and keep the total moment of momentum conserved. The applications of these results to small landing robots and multi-segment spacecraft are anticipated.