Scientists using accelerometer backpacks to study 'flying' lemur's gliding behaviour

Washington, February 8 : University of California, Berkeley scientists are studying the gliding behaviour of "flying" lemurs called the colugo by fixing miniature accelerometer backpacks on their bodies.

The researchers say that the findings from the study in Singapore could be helpful in advancing understanding of the behaviour and biomechanics of gliding animals ranging from ants and snakes to squirrels. The findings may also help improve the design of flexible winged aircraft such as hang gliders and micro air vehicles, they say.

The researchers say that the colugo, even though is not a lemur, is nevertheless a close relative of the primates that include lemurs as well as humans. Common throughout Southeast Asia, it looks like a very large squirrel with membranous skin stretching from each limb and even between its toes to catch the wind and work as a parachute.

When fully spread, the skin flaps reach the size of a large doormat.

"This makes them quite manoeuvrable," said Greg Byrnes, a graduate student in UC Berkeley's Department of Integrative Biology, while writing a report published in the journal Proceedings of the Royal Society.

Byrnes says that he has observed colugos gliding toward one tree and, seemingly changing their minds in midair, dodge around it and land on a different tree.

"I've seen animals gliding and get to a place where foliage is dense, and they will actually collapse their membrane, haul through the leaves and then open up and glide some more. Obstacles are not much of an issue for them," he said.

Colugos captured in forested areas of Singapore were fitted with accelerometer backpacks, and released to go about their business for a few days until the backpack fell off and could be retrieved. A radio tag on the backpack allowed Byrnes to track the location of the colugo every hour or so during the night, and to locate the instrument after it had fallen off.

Analysing the recorded data, the researchers came to the conclusion that colugos push off from trees more forcefully for long jumps, but that they quickly reach terminal velocity once they spread their limbs into a parachute, and thus their landing force remains about the same no matter how far they glide.

The researchers said that the landing forces increase with distance only for short leaps, a few times their body length of 75 centimetres, or about 30 inches, probably because they land with two limbs instead of four. However, once all four limbs are spread out, the colugo may even get enough lift to land more softly the farther it travels.

Byrnes believes that this fits with aerodynamic models.

The study's authors write that the colugo's ability to change its posture for aerial braking just prior to landing is "probably an important trait in the transition from leaping to gliding. It enables the gliders to reduce the impact forces in long glides, thus reducing the risk of injury."

Byrnes is planning to continue studying the colugo's gliding behaviour, and to reduce the size of the data logger in order to study the gliding of smaller mammals, in particular the American "flying" squirrel.

"We're interested in the effect of body size on gliding behaviour, and 'flying' squirrels have a wider range of sizes than colugos. Gliding has evolved several times, so by looking at behaviour in many species, we also can understand the evolution of gliding," he said.

ANI