Springboard divers get a major boost when bouncing repeatedly on a flexible board. However, for most animals that bound from a bendy surface, the results are disappointing. Tree frogs and other arboreal species that don't bounce up and down – and are unable to capitalise on the rebound – lose mechanical energy when they launch from a springy surface. Henry Astley, Alison Haruta and Tom Roberts from Brown University, USA, say, ‘In all species previously examined, animals lost contact with the substrate prior to recoil, preventing any recovery of the energy imparted to the substrate’. The trio wondered whether Cuban tree frogs could be even more compromised, thanks to their extraordinarily long legs. Building a springy frog perch from a length of latex tubing stretched to varying degrees to alter the stiffness, Astley, Haruta and Roberts tickled the frogs with a brush and filmed their take-offs with high-speed cameras to capture every detail of the launch.
Describing how the most flexible perch deflected by 34% of the frog's leg length, while the least flexible perch only extended by 10%, the team then calculated how much energy was stored in the perch during a leap and was impressed to see that almost half of this energy was returned to the frog by the stiffer perches as they recoiled just before the animal's feet lost contact to thrust the animal into the air. ‘The recoil of an elastic perch presents an opportunity to recover some of this energy to reduce the potential detriment to jump performance’, says the team, and Astley adds, ‘These tree frogs are the first known examples of an animal recovering perch energy from the perch during a jump from a static posture’. They also suspect that the frogs’ long legs and sticky toes could help them to stay in contact with the perch for longer to take advantage of the rebound boost.
