Meeting Abstract
The avian hindlimb plays an important role in takeoff by helping to launch the bird into the air. During terrestrial takeoffs, hindlimb function resembles a ballistic jump. Many birds require long water runways for aquatic takeoffs. However, mallard ducks are capable of nearly vertical takeoffs from both water and land. In this study, we measured the kinematics of the mallard hindlimb during terrestrial and aquatic takeoffs. Force production varies between terrestrial and aquatic media. Hindlimb force production during a terrestrial jump depends on muscle force output, while the hydrodynamic force produced by moving the foot through water depends on the square of the hindlimb velocity. We expect that hindlimb kinematics vary between takeoffs from water and land, with the former favoring higher velocities. Preliminary data (n=2 animals with 3 terrestrial and 3 aquatic trials per animal) suggest that while angular excursions at the metatarsal phalangeal joint are similar between terrestrial and aquatic takeoffs, the ankle undergoes larger angular excursions during aquatic (~96 °) than terrestrial (~79 °) takeoffs. The duration of aquatic takeoffs (~0.10 s) is similar to or shorter than terrestrial takeoffs (~0.12 s). Thus, angular velocity at the ankle is higher during aquatic takeoffs (~1000 °/s) than terrestrial (~650 °/s), which is consistent with our hypothesis that takeoffs from water will favor larger hindlimb velocities than from land. These results raise interesting questions about the relative contribution of hindlimb force production for aquatic vs terrestrial takeoffs and about the function of ankle extensors, which must power both behaviors that require either high force output (terrestrial takeoff) or high shortening velocity (aquatic takeoff).
