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First published online March 12, 2009
Journal of Experimental Biology 212, 945-953 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026161
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Bats go head-under-heels: the biomechanics of landing on a ceiling

Daniel K. Riskin1,*, Joseph W. Bahlman1, Tatjana Y. Hubel2, John M. Ratcliffe3, Thomas H. Kunz4 and Sharon M. Swartz1,2

1 Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA
2 Division of Engineering, Brown University, Providence, RI 02912, USA
3 Institute of Biology, University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
4 Center for Ecology and Conservation Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA


Figure 1
Figure 1
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  		Fig. 1. Landing sequences of bats: (A) a four-point landing by Cynopterus brachyotis, (B) right-handed and (C) left-handed two-point landings by Carollia perspicillata, and (D) right-handed and (E) left-handed landings by Glossophaga soricina. Peak impact force into the ceiling occurs at t=0.00.

 

Figure 2
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  		Fig. 2. Pitch angle (black), yaw angle (red) and roll angle (blue) of bats landing on a force platform: (A) Cynopterus brachyotis, (B–E) Carollia perspicillata and (F,G) Glossophaga soricina. Broken lines are at ±180 deg. and error bars extend one standard deviation above and below the mean. Time=0 is the time of peak impact force into the ceiling. C. brachyotis always made a four-point landing (A). Members of the other two species performed right-handed landings (B,F) or left-handed landings (C,G). Right-handed landings and left-handed landings were similar but with the yaw and roll angles changing in the opposite direction. Some C. perspicillata performed a variation of the right-handed (D) and left-handed (E) landings where yaw rotation was initiated later and thus made a smaller contribution to overall rotation than pitch did. Sample sizes are: A, 29; B, 22; C, 13; D, 4; E, 6; F, 15, and G, 32.

 

Figure 3
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  		Fig. 3. Schematic of (A) a four-point landing and (B) a right-handed two-point landing, based on the mean kinematic data from Fig. 2A and 2B, respectively. As the bat landed on the ceiling, we used the difference between the body-referenced coordinate system (xb, yb, zb) and the global coordinate system (xg, yg, zg) to describe the orientation of the bat. The xb vector points anteriorly, yb points laterally to the bat's right and zb points ventrally. The xg vector is the horizontal projection of xb at t=–0.2 s, zg is vertical down and yg is the cross product of zg and xg.

 

Figure 4
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  		Fig. 4. Typical force profiles for (A) a four-point landing Cynopterus brachyotis and (B) a two-point landing Carollia perspicillata. The green line shows vertical force, with positive numbers representing forces into the ceiling and negative numbers away from the ceiling. Red and blue lines are forces in two orthogonal horizontal axes. Force profiles for G. soricina were very similar to those of C. perspicillata and are therefore not shown. The magnitude of the peak impact force (into the ceiling and, later, away from the ceiling) for four-point landing bats was typically larger than those of bats using two-point landings. The oscillations in horizontal force that occur after landing in B are the result of the bat swinging from side to side as it hangs from its toes after landing.

 

Figure 5
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  		Fig. 5. Box plots of (A) peak impact force into the ceiling (Fpeak-up) and (B) peak pulling force down from the ceiling (Fpeak-down) over the course of each trial for all 13 individuals tested in this study. Each individual occupies its own position on the x-axis. N=10 trials for all individuals except C. brachyotis for which sample sizes are (from left to right in figure) N=11, N=10 and N=8. Fpeak-up and Fpeak-down were larger in magnitude for C. brachyotis than they were for either of the other two species (P<0.0001 and P<0.005, respectively). Circles represent outliers.

 

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© The Company of Biologists Ltd 2009