On the Wings of Dragons

14 January 2015

If you’ve ever been on a walk in the rainforests of Borneo you may have experienced this not-uncommon occurrence: out of the corner of your eye you glimpse a leaf falling down from the canopy, only instead of it continuing down to the forest floor it abruptly vanishes onto the side of a tree. It might take a few moments to register, but suddenly you realize that there was just something not quite right about the trajectory of that leaf. A keen eye (and often a pair of binoculars) and a scan of the tree trunk will reveal the real culprit of the fraud: a gliding lizard. And, as it turns out, you were meant to be deceived.

With over 40 species distributed across Asia (and 10 in Borneo), Draco lizards are perhaps the most effective gliders in the animal kingdom. Although typically measuring less than 20 cm from nose to tail tip, they have been recorded gliding over 50 meters in a single leap. This is achieved by extending a flap of skin (patagium) on their sides which is supported by movable ribs, effectively turning the reptile into a miniature frisbee. Steering in mid-flight is controlled by the tail and perhaps also by the front legs which are pressed over the top of the wings while airborne.

Within a forest habitat the ability to glide is an enormous advantage and this may account for why these lizards are so successful and species diverse. Traveling from tree to tree with ease, Draco are able to forage over a greater area (they feed predominantly on ants) as well as escape certain predators without ever having to descend to the ground. Flight, however, brings with it certain dangers, and although the lizards are highly camouflaged when perched against tree bark with their wings concealed, their movements through the air put them at risk from detection by keen-eyed predatory birds.

A newly published paper in Biology Letters (see link below), with research supported by the National Geographic Society, finds evidence that the patagia of several Draco species mimic the color of dead leaves, providing the lizards with effective camouflage even while in flight. Researchers measured the color of Draco wing membranes and compared it with the color of fallen leaves occurring in the vicinity. Amazingly, a color correlation was found not only between each species’ patagia and the color of the most abundant falling leaves in their preferred habitat, but two separate populations of a single species (D. cornutus) matched the predominant leaf color at the different locations they were found in: reddish-brown mangrove leaves vs. dark-brown lowland forest leaves. More work remains to be done to substantiate this trend in other populations and species of Draco.

Studies like this continue to decipher the amazing minutiae of adaptations that rainforest organisms possess and show that, in a habitat teeming with predators and prey, deception plays no small part in the struggle for survival. Next time you see a leaf falling down through the forest, have a second look – in the jungles of Borneo things aren’t always what they seem.

Draco cornutus

References:

Klomp DA, Stuart-Fox D, Das I, Ord TJ. 2014 Marked colour divergence in the gliding membranes of a tropical lizard mirrors population differences in the colour of falling leaves. Biol. Lett. 10: 20140776. http://dx.doi.org/10.1098/rsbl.2014.0776


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