04 August 2011

Singapore's cool colugos: why they glide

Studying Singapore's colugos, researchers including our very own Norman Lim have discovered why these animals glide.
Colugo (Cenopcephalus variegatus)
Although called flying lemurs, these creatures are not lemurs and they don't fly!

Colugos are actually not closely related to lemurs and are instead distantly related to us primates. Colugos glide and don't fly. Norman's earlier studies revealed, among others, that these awesome animals are quite common in our forests! But it requires a keen eye to spot them as they are well camouflaged and more active at night.

Colugos glide to save time, not energy
EurekAlert 28 Jul 11;

Gripping tightly to a tree trunk, at first sight a colugo might be mistaken for a lemur. However, when this animal leaps it launches into a graceful glide, spreading wide the enormous membrane that spans its legs and tail to cover distances of up to 150m.

So, when Greg Byrnes and his colleague Andrew Spence from the University of California, Berkeley, USA, were looking around for a mammal to carry the accelerometer/radio transmitter backpacks that the duo designed to track animals in the field, the colugo was an obvious choice. 'They are a large glider and it was an opportunity to learn about an animal that we didn't know much about,' says Byrnes.

Admitting that they were initially interested in the natural history of these charismatic creatures, Byrnes realised that they could use the information gathered to find out about the cost of the colugo's gliding lifestyle.

Flying to Singapore, Byrnes teamed up with Norman Lim to track the gliding mammals and the team discovered that instead of saving energy, colugos glide to save time. They publish this discovery in The Journal of Experimental Biology at http://jeb.biologists.org/content/214/16/2690.abstract.

Describing how some of the nocturnal colugos roost low in the forest, Byrnes was able to capture six of the mammals and glue the accelerometer packs to their backs before allowing them to scurry back up their trees for their first glide of the night. Explaining that the data loggers were able to collect data for 3 days, Byrnes and Lim tracked the animals until the data loggers eventually fell off and they were able to retrieve them several weeks later.

Back in Berkeley, Byrnes, Spence and Thomas Libby had the unenviable task of managing the colossal amount of data collected: 'We were sampling at 100Hz for days,' explains Byrnes. According to Byrnes, there is a distinctive acceleration profile when they glide. 'What you see is the leap and the landing when there is this sweeping acceleration, so it's easy to pick out their glides,' he says. Eventually, the trio converted each animal's acceleration traces into velocities – as they scaled trees and glided – and then they calculated the distances that the animals covered.

Analysing the glide trajectories, the team realised that the colugos only climb a relatively small height to achieve their lengthy shallow glides. 'The average was 8 m for an animal that is gliding 30m,' says Byrnes. But how much energy were they using to cover that distance?

Basing their calculations on the amount of energy used by small climbing primates – close relatives of the colugo – the trio calculated the energy used by a colugo ascending a tree to initiate a glide. Then they calculated the amount of energy that the animals would use if they had clambered through the canopy to cover the glide distance and were amazed to see that instead of saving energy, the colugos were using 1.5 times more energy. 'This was a surprise, as the dogma has always been that gliding is cheaper,' says Byrnes.

However, one thing was clear: gliding was faster. 'If you watch the animals move through the trees they move pretty slowly,' says Byrnes, 'But they can go 10 times as fast and cover long distances gliding so they can spend more time foraging,' he explains. Gliding could also protect colugos from dangerous predators and reduce the risks of climbing on spindly branches, so it could be more of a long-term benefit than simply saving energy.

Byrnes, G., Libby, T., Lim, N. T.-L. and Spence, A. J. (2011). Gliding saves time but not energy in Malayan colugos. J. Exp. Biol. 214, 2690-2696.

Here's a great slideshow from the BBC with photos and stories of how measuring instrument 'packs' were attached to our colugos, with a lovely view of our rainforests. Singapore's forests are awesome!
This story is also reported in Scientific American, Nature blog and ScienceDaily.

Sadly, these gentle creatures are sometimes cruelly hunted in our forests. There was an incident of a mother colugo that was seriously injured by a poacher with a slingshot. Her baby survived the mother's fall, but eventually died too despite best effort to care for it.

I first got to know Norman helping him with his colugo survey in Singapore's forests many years ago. From him I learnt to be quiet and how to spot colugos and many different kinds of forest animals. Here's my rather dated write up about Norman. Norman has since also started studying our wild pangolins. He also sighted the Malayan porcupine which has not been seen on Singapore mainland for 50 years!
Photo from Norman's page.

We need dedicated researchers such as Norman to learn and do more for Singapore fascinating biodiversity!

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