Herps in the Sky? – Part 1

Aerial Movement is something that has evolved (independently) many times in the animal kingdom.There are two types of Aerial Movement: True flight and Gliding/Parachuting. They are useful adaptations, especially in rainforests, where they enable canopy dwellers to travel easily from tree to tree, without expending too much energy.

True flight is something that is restricted to birds, bats and insects. It is distinguished from gliding and parachuting in that flying animals are able to produce thrust, to sustain their upward path. This is done by way of the “flight stroke”. It is an important thing to note that no herps are capable of true flight. However, some herptiles have evolved ingenious methods of gliding to get around their respective habitats.

In this four-part series of posts, we discuss the various South-East Asian herps that are capable of gliding or parachuting.

PART 1 – “FLYING SNAKES”

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A beautiful Paradise Tree Snake from Sungei Buloh Wetland Reserve

Chrysopelea, is a genus of snakes from South and South-East Asia, that are also known as ‘flying snakes’. Two species, the Paradise Tree Snake (C. paradisi) and the Twin-Barred Tree Snake (C. pelias) are known to be native to Singapore, while a third species, the Golden Tree Snake (C. ornata), has been recorded [1][2] in various localities. It is not, however, native to Singapore.

The Twin-Barred Tree Snake
The Twin-Barred Tree Snake (C. pelias). Image Credit: Nick Baker, ecologyasia.com

In most terrestrial gliders, gliding begins with a take-off. The take-off is usually accomplished by rapidly straightening bent limbs. In snakes, which lack limbs altogether, this poses a challenge. Members of the Chrysopelea genus are unique, in that they are the only limbless animals that are known to glide through the air!

SO HOW DO THEY DO IT?
The gliding behaviour of Chrysopelea was observed as early as 1899[3]. But the mechanism of this behaviour was poorly understood for a very long time, until recently.

An interesting experiment was conducted in NUS in 1997. The flying snakes were placed in boxes on the third floor of the NUS Physics building. A panel in the front of the box was removed and the snake would jump out on its own to glide over a distance. You can see the pictures at this link. Another similar project was conducted at the Singapore Zoo in 2000, to map out 3-D information on the glide trajectory of C. paradisi. After several years of such intensive research, the gliding behaviour of the flying snake became better understood[4].

Step 1: The snake forms a J-shaped bend by dropping the forebody off the end of a branch. The rear end of the body and the tail anchor onto the branch

Step 2: The snake then accelerates its forebody upwards and forwards, with the rear end of the body still anchored to the branch. As the snake moves away from the branch, it releases its grip and is fully airborne. At this point, it begins flattening its body.

Step 3: The cylindrical shape of snakes is not very aerodynamic. So, Chrysopelea splays out its ribs to flatten its body. The ventral side of the snake will have a concavity, causing its cross-section resemble a frisbee. In doing so, it turns its body into a “wing”, with which it can glide. In doing this, the snake practically doubles in width!

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The flattening of the snake’s body is evident in this photo!

Step 4: The flying snake moves in an undulating, “S”-shaped motion in the air. It catches the air beneath its body and glides over large distances. It is even able to maneuver to avoid obstacles and threats. A study done in 1970 even recorded an instance of a C. ornata specimen changing direction 180in mid-air to land near the base of the tower from which it was released[5]!

IN SINGAPORE?
Yes! Some of these amazing snakes can be found in Singapore! If you’re lucky and observant, you might get the chance to spot one. They are not harmful to humans, and feed on lizards and other small animals. Look out for these amazing snakes next time you’re in a nature reserve or park!

REFERENCES
[1] – 
Thomas, N., & Boopal, A. (2014). Golden gliding snake at Shenton Way. Singapore Biodiversity Records 2014, 51-51. <link>
[2] – Maury, N., & Low, M. (2015). Golden gliding snake at Lim Chu Kang. Singapore Biodiversity Records 2015, 76-76. <link>
[3] – Daly, M. (1899). A Flying Snake. The Journal of the Bombay Natural History Society, 12, 589-589. <link>
[4] – Socha, J. (2011). Gliding Flight in Chrysopelea: Turning a Snake into a Wing. Integrative and Comparative Biology, 1-14. doi:10.1093/icb/icr092 <link>
[5] – Heyer, R., & Pongsapipatana, S. (1970). Gliding speeds of Ptychozoon lionatum (Reptilia: Gekkonidae) and Chrysopelea ornata (Reptilia: Colubridae). Herpetologica, 26(3), 317-319. <link>

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