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First published online April 18, 2006
Journal of Experimental Biology 209, 1725-1736 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02186

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Terrestrial locomotion of the New Zealand short-tailed bat Mystacina tuberculata and the common vampire bat Desmodus rotundus

Daniel K. Riskin^1,*, Stuart Parsons², William A. Schutt, Jr³, Gerald G. Carter¹ and John W. Hermanson¹

¹ Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
² School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand
³ Biology Department, CW Post College of Long Island University, Brookville, NY 11548, USA

View larger version (95K): [in a new window]   Fig. 1. Representative stride cycles on the treadmill of D. rotundus in lateral view (A) walking at 0.12 m s–1 and (B) bounding at 0.60 m s–1; (C) M. tuberculata moving at 0.35 m s–1. The time between frames differs in the three sequences (40, 24 and 16 ms, respectively). The background is a 1 cm2 grid. Dorsal views of the same three sequences are shown in D, E and F, respectively.

View larger version (10K): [in a new window]   Fig. 2. Duty factor (the proportion of a stride cycle for which a given limb is in contact with the ground) of treadmill trials for (A) walking D. rotundus, (B) bounding D. rotundus and (C) M. tuberculata. Blue circles represent the means of left and right forelimbs in each trial, and red squares the means of hindlimbs. Each plot includes a horizontal line at duty factor=0.5, the kinematic separation point between walks (duty factor >0.5) and runs (duty factor <0.5) (Hildebrand, 1976).

View larger version (11K): [in a new window]   Fig. 3. The gait of M. tuberculata (blue) demonstrates a linear increase in stride frequency with speed, just as the gaits of many other tetrapods do (Heglund and Taylor, 1988). The broken red lines represent the linear best fit regressions for walking (left) and bounding (right) gaits of D. rotundus, truncated at their point of intersection (see Riskin and Hermanson, 2005).

View larger version (17K): [in a new window]   Fig. 4. Energetics of two separate stride cycles, left hind footfall to left hind footfall, of M. tuberculata performing (A) a kinetic walk-like stride cycle (body mass=14.0 g, speed=0.27 m s–1, %congruity= 19.3%, %recovery=59.5%), and (B) a kinetic run-like stride cycle (body mass=15.5 g, speed=0.28 m s–1, %congruity=60.0%, %recovery=24.0%). Though speed is similar in these two trials, the energetics of the former feature greater pendulum-like changes in EK and EP than the latter. Despite such variability in COM energetics from trial to trial, M. tuberculata did not transition from a kinetic walk to a kinetic run with increasing speed.

View larger version (8K): [in a new window]   Fig. 5. Magnitudes of oscillations in (A) EKV, (B) EKF, (C) EKL, (D) EP and (E) ETOT of M. tuberculata walking across the force plates at a range of speeds. Bats increased the magnitudes of fore–aft and vertical EK oscillations with speed, but not of lateral EK nor of EP.

View larger version (11K): [in a new window]   Fig. 6. (A) %congruity and (B) %recovery and of M. tuberculata crossing the force plates at a range of speeds. The considerable variability of values for both these descriptive statistics supports our observation that the patterns of vertical body movement were extremely variable from trial to trial, both on force plates and on the treadmill. A transition from an energetic walk to an energetic run with increased speed would be reflected by an increasing %congruity and decreasing %recovery, but neither regression has a slope significantly different from zero.

View larger version (27K): [in a new window]   Fig. 7. A Hildebrand gait plot for the walking gait of D. rotundus (red) and the single gait of M. tuberculata (blue). Duty factor is the percent of the stride cycle for which the feet were in contact with the ground, averaged for all four limbs in a stride cycle. Limb phase is the percent of the stride cycle that elapsed between left hindlimb footfall, and left forelimb footfall. The shaded area encloses 1178 symmetrical gait plots from 156 genera of tetrapods (see Hildebrand, 1985).

View larger version (11K): [in a new window]   Fig. 8. Footfall patterns, beginning and ending with left hind footfall, on the treadmill for (A) bounding D. rotundus, (B) a bounding quadrupedal rodent (see Hildebrand, 1985), (C) walking D. rotundus, and (D) M. tuberculata using their single gait. Solid bars indicate the time that a foot is in contact with the ground. Open bars represent one standard deviation above and below the mean. F, fore; H, hind; L, left; R, right. Note that the bounding gait of D. rotundus is superficially similar to the bounding rodent gait, but with the footfall patterns of the forelimbs and hindlimbs reversed.