Biomechanics of terrestrial locomotion in bats
Riskin, Daniel K.
This dissertation concerns the way in which bats move on the ground. Chapter one is a literature review on the subject, from an evolutionary perspective, that includes contributions from this thesis. In chapter two, I test an hypothesis frequently used to explain the poor crawling abilities of bats compared with mammals that do not fly. According to that hypothesis, most bats shuffle awkwardly because their hindlimbs are too long and slender to support their body weights, but vampire bats walk well because their hindlimbs are more robust than those of other bats. I used force plates to test a prediction of the hindlimb-strength hypothesis that the peak hindlimb forces of walking vampire bats should be greater than the forces exerted by the legs of poorly crawling bats. I found that shuffling bats (Pteronotus parnellii) exert larger hindlimb forces than walking vampire bats do (Desmodus rotundus, Diaemus youngi). Additionally, I used a simple engineering model of bone stress to demonstrate that the hindlimbs of vampire bats fall within the range of shapes seen in bats that do not walk well. These results do not support the hindlimb-strength hypothesis. In chapter three, I describe the running gait of Common Vampire Bats (D. rotundus). At low speeds, these bats use a lateral sequence walking gait, similar to those of other tetrapods, but switch at higher speeds to a bounding gait that is powered by the forelimbs. This gait is unique to vampire bats, and appears to be independently evolved form the running gaits of other tetrapods. In chapter four, I compare the kinematics of locomotion in Common Vampire Bats to those of another terrestrially adept species, New Zealand short-tailed bats (Mystacina tuberculata). The latter use a lateral sequence walk similar to that of D. rotundus and other tetrapods, but do not perform the bounding run. Using force plates to examine the kinetics of their single kinematic gait, I found that the gait of M. tuberculata is a kinetically run-like, and does not shift from a kinetic walk to kinetic run with increased speed the way the gaits of some other animals do.
dissertation or thesis