Posts on Fauna

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

A Tale of Two Kitties

30 May 2014

Several days ago whilst hiking up a hill in Danum Valley to check on one of my camera traps, I had a chance encounter with one of Borneo’s most beautiful creatures: a Marbled Cat (Pardofelis marmorata), the first I have ever seen. I was about to ford a creek at the bottom of a small gulley and noticed something moving in the undergrowth on the opposite bank. The cat was so perfectly camouflaged that I didn’t realize I was staring directly at it until it moved again. About half a metre in length with a tail at least as long again, it was beautifully patterned with dark and tan blotches. It had seen me already (of course) and was slowly slinking away up the stream bank.

As luck would have it I had just left my camera in a hide a few hundred meters down the trail so taking a photo was out of the question. Without thinking I raised my hand to my lips and squeaked out a simple rodent alarm call. The cat stopped in its tracks and turned around, staring at me. Unbelievably it then began stalking back down the stream bank towards me until it reached a point on the opposite bank less than 4 meters from where I stood. We locked eyes for a few seconds, the cat trying to decide exactly what was going on, and me just trying to savor as much of the experience as I could while keeping my heart rate at a reasonable level. A moment later it turned and sulked away, uttering a low growl as it went, and disappeared quickly among the underbrush.

I glanced at my watch: 10:30 AM sharp. Bright sunny day and blue sky. While we normally think of the shy wild rainforest cats as strictly nocturnal, or even crepuscular creatures, it seems that the Marbled Cat is often active during the middle of the day. My good friend Dr. Jedediah Brodie, who has done a enormous amount of camera trapping in Borneo for his research on mammal ecology, thinks that this cat may use daylight hours as a means of avoiding confrontations with the apex carnivore of Borneo rainforests, the Sunda Clouded Leopard (Neofelis diardi diardi), which is more active at night and early morning. Although confusingly similar in coloration, the Clouded Leopard is several times larger than the Marbled Cat and wherever present would occupy the role of top predator without dispute.

As if just to prove a point, twenty minutes later and another 500 meters ahead on the trail I crouched down to examine the catch on my camera trap which had been running for the past two weeks, and a possible reason for the Marbled Cat’s diurnal habits became clear – a Clouded Leopard had been on the prowl just the night before:

Sunda Clouded Leopard (Neofelis diardi)

With five species of wild cats, Borneo is exceptionally rich in felid species even were it not an island. In addition to the Marbled Cat and Clouded Leopard, Borneo is also home to the Leopard Cat (Prionailurus bengalensis), Flat-headed Cat (Prionailurus planiceps), and arguably the least known of all the world’s cat species, the rare endemic Bay Cat (Catopuma badia). All except for the Leopard Cat, which survives well in disturbed habitats, are under threat due to habitat loss and poaching, making them the focus of long-term studies and conservation efforts.

New Species of Gliding Frog from Borneo

18 September 2013

Few animals seem to encapsulate the magical qualities of the Bornean jungle more than gliding frogs. Armed with huge webbed feet and flaps of skin along their limbs, these colorful amphibians sport the uncanny ability to paraglide down from the tree tops and even change directions in mid-flight. Once, during a visit to the canopy walkway in Danum Valley Conservation Area in Sabah, I witnessed firsthand just how effective the gliding ability of these frogs can be. Upon arriving at a tree platform in the middle of the walkway, perhaps 50 meters above the forest floor, I noticed a small orange frog (Rhacophorus pardalis) perched on one of the wooden planks near the edge. As I approached for a closer look it abruptly leapt off the platform and I watched as it soared down through the air, carved a wide arc around a lower tree and disappeared into the forest below.

Several gliding frog species occur in Borneo, all in the genus Rhacophorus and all equally charming with their gaudy colors and oversized (seemingly ungainly) floppy feet. The most well-known is undoubtedly the large and spectacular Wallace’s Flying Frog (Rhacophorus nigropalmatus), made famous by Alfred Russel Wallace’s description and illustration in The Malay Archipelago. Smaller, but no less attractive is the Harlequin Flying Frog (Rhacophorus pardalis) which is perhaps the most common of the species, being found all across the island around muddy pools of water in the forest.

Last month a scientific paper published in Current Herpetology brought to light an entirely new species, the Bornean Gliding Frog (Rhacophorus borneensis). Perhaps the most colorful of all the Rhacophorids, R. borneensis is a pale lime-green with an orange underside and interspersed with patches of black and brilliant sky-blue. This frog had been known previously from a few scattered collections and photos from Sarawak and Sabah, but was thought to belong to the Javan Flying Frog (Rhacophours reinwardti). The new research compared both color patterns, size, and DNA, and showed that the Bornean specimens are indeed distinct from R. reinwardti, which is now believed to occur only in Java.

Rhacophorus borneensis

Like other gliders, R. borneensis is a true tree frog, and it is believed to live almost its entire adult life in the forest canopy, descending to pools of water only to breed and lay eggs. Simply judging by how rare encounters with this species are, its visits to ground level are probably even more infrequent than R. nigropalmatus or R. pardalis. The presence of R. borneensis in the forest is often only detected by the distinctive call of the male, sounding somewhat like a woodpecker drumming on a hollow tree.

So far the life-history of the Bornean Gliding Frog remains almost completely unstudied, but further research is certainly warranted for this newest member of Borneo’s magnificent gliders.

References:

M. Matsui, T. Shimada, A. Sudin. A New Gliding frog of the Genus Rhacophorus from Borneo. Current Herpetology, August 2013; 32(2): 112-124.


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