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Landings Hard for Some Bats

Photonics.com
Mar 2009
PROVIDENCE, R.I., March 20, 2009 – Using sophisticated motion-capture cameras to document for the first time how bats arrive at their daytime roosts, biologists uncovered a surprising fact – different species come in for much harder landings than others.

A Brown University-led research team was first to document the landing approaches of bats, using three synchronized digital cameras to record them at high speed. The group studied two cave-dwelling species and one tree-roosting species and discovered the different approaches to their perches.
Bat.jpg
Thanks to a first-ever motion-capture filming of bats arriving at their roosts, a Brown University-led research team has found that bat species have unique landing styles. (Photo: Brown University)
“Hanging upside down is what bats do,” said Daniel Riskin, a postdoctoral researcher in the ecology and evolutionary biology department at Brown and lead author on a paper published in the Journal of Experimental Biology. “We’ve known this. But this is the first time anyone has measured how they land.”

Using sophisticated motion-capture cameras in a special flight enclosure, the team filmed each species of bat as it swooped toward a latticed landing pad and landed on it. Cynopterus brachyotis, a tree-roosting bat common in tropical parts of southeast Asia, executed a half-backflip as it swooped upward to the landing site, landing as its hind legs and thumbs touched the pad simultaneously – a four-point landing, the group observed.

The landing is hard, Riskin noted, with an impact force more than four times the species’ body weight. (Watch the video.)

The team then turned its attention to two cave-roosting species, Carollia perspicillata and Glossophaga soricina. These bats, common in Central and South America, approach their landing target with a vertical pitch and then, at the last instant, yaw to the left or to the right – executing a cartwheel of sorts – before grasping the landing pad with just their hind legs. (Watch the video.) 

The two-point landing is much gentler than the impact force exerted by the tree-roosting bats, the researchers observed; the cave-roosting bats have a landing impact force of just one-third of their body weight.

There are about 1200 recognized bat species worldwide, so Riskin was cautious about not drawing any grand conclusions. Still, he said, the fact that the team has documented that bats land differently could open new insights into a species that makes up roughly one-fifth of all mammals on earth.

“It’s opening the door to how bats evolved,” Riskin said. “You can say that bats have been hanging upside down since they first evolved, and it has probably been one of the keys to their worldwide success.”

Other Brown researchers who worked on the paper include Sharon Swartz, associate professor of biology; Tatjana Hubel, a postdoctoral researcher; and Joseph Bahlman, a graduate student. John Ratcliffe, a biologist at the University of Southern Denmark, and Thomas Kunz, a biologist at Boston University, contributed to the paper.

The research was funded by the National Science Foundation, Air Force Office of Scientific Research, Sigma Xi in the US, The Natural Sciences and Engineering Research Council of Canada and the Danish Natural Sciences Research Council.

For more information, visit: www.brown.edu


GLOSSARY
camera
A light-tight box that receives light from an object or scene and focuses it to form an image on a light-sensitive material or a detector. The camera generally contains a lens of variable aperture and a shutter of variable speed to precisely control the exposure. In an electronic imaging system, the camera does not use chemical means to store the image, but takes advantage of the sensitivity of various detectors to different bands of the electromagnetic spectrum. These sensors are transducers...
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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