by Kai Kolodziej
I guess many of us have seen flying reptiles in films and movies, and I am not talking about the (sadly fictional) massive fire breathing dragons in Game of Thrones or similar series.I am talking about the real flying reptiles: flying snakes (Chrysopelea sp.), flying lizards (Draco sp.) or even flying geckos (Ptychozoon sp.), but don’t forget our amphibian friends like the flying frogs (Rhacophorus sp.), just to name the most famous ones. Many of them are regularly shown in documentaries about Southeast Asian rainforests.
This is the first thing we notice when talking about flying herps, nearly all of them are native to Southeast Asia. This regional phenomenon is not exclusive to herps, but is also seen in some of the native mammals.
So, there must be a reason for this occurrence across several groups of animals? As a matter of fact, the main reason for the gliding ability of vertebrates in the Asian rainforests is the structure of the habitat. Even if rainforests look quite the same on the first glance, they are vastly different in Africa, Asia or the Neotropics. In the Neotropics, there is a higher density of lianas, an important structure in rainforests that provide horizontal pathways between different trees. With less lianas, arboreal animals would have to leave the safety of the canopy and access the next tree by walking on the ground, potentially exposing them to a higher risk of predation.
Another feature of Asian rainforests are the high trees, the so called emergent layer. The higher density of emergent trees together with the lower density of lianas in the rainforests of Southeast Asia made the evolution of gliding vertebrae not only possible but arguably necessary. You may have noticed that although they are called “flying” snakes, geckos, and frogs, I speak of a gliding ability and not flying. Flying is referred to as an active powered flight, whereas gliding isn’t powered. But how good are these gliders? Can they maneuver their flight or do they just slow down their fall so that they won’t get hurt? This question is easier answered for the reptiles, as the gliding ability of the flying frogs was never compared to their kin.
Firstly, we will take a look at the flying frogs, Rhacophorus nigropalmatus in particular. One study compared this species to non-flying frogs of the genus Polypedates. Surprisingly, the gliding performance (in terms of distance) in the non-flying frogs was better than in the already adapted flying frog. But together, with behavioral changes, the flying frogs are able to maneuver their flight which appears to be more important to them than gliding as far as possible.
The several flying reptiles were compared in 2005 and the results found that flying geckos are the worst gliders in terms of the gliding angle. Flying snakes are on par with mammalian gliders, like sugar gliders, which is amazing considering the lack of limbs. The best gliders by far are flying lizards of the genus Draco, but who would have thought different if a genus is named Draco? Considering these results, there may be a predator/prey relationship between Draco and Chrysopelea, which resulted in an evolutionary arms race. Chrysopelea are faster gliders but Draco is much better in maneuvering, which makes sense if you think about it, however, more studies are needed to evaluate this relationship.
Recent studies about Chrysopelea showed that they are indeed capable of maneuverability and even stabilizing their flight. They use aerial undulation to stabilize their flight that is especially recognizable in long glides. Due to this behaviour, Chrysopelea are able to turn in flight and glide greater distances.
We still have much to learn about flying herps, the relationships between the different species, and the capabilities of this “flying” ability.
Literature:
Emmons Louise und Gentry A.H. (1983): Tropical Forest Structure and the Distribution of Gliding and Prehensile-Tailed Vertebrates. American Naturalist 121 (4).
Socha John J, Labarbera Michael, O’Dempsey Tony (2005): A 3-D kinematic analysis of gliding in a flying snake, Chrysopelea paradise. Journal of Experimental Biology 208 (10).
Yeaton Isaac J. et al (2020): Undulation enables gliding in flying snakes. Nature Physics.
