Although active flight is known to have evolved only in birds, bats, insects, and pterosaurs, gliding--"controlled descent by an organism that converts gravitational potential energy to useful aerodynamic work" (Dudley et al. 2007)--is more broadly distributed. Gliding ability has evolved in more than 30 phylogenetically independent lineages of arboreal vertebrates (Dudley et al. 2007), with a variety of morphological modifications and behaviors to make it work. Unlike most of these other gliding vertebrates, Chrysopelea snakes such as the Golden Tree Snake neither create bilateral wings nor use skin as a flight surface, but instead double in width and form a concave bottom surface, creating a flattened whole-body "wing". When a Chrysopelea "flying" snake moves through the air, it passes lateral traveling waves posteriorly along its long, dorsoventrally flattened body. The whole snake becomes a ‘"wing"’ that constantly reconfigures throughout flight, moving in a complex motion in three dimensions, making its aerial behavior the most dynamic of any vertebrate glider. (Socha and LaBarbera 2005; Socha et al. 2010 and references therein)
In experiments in which C. ornata individuals were launched from a 41 meter tower, snakes traveled up to a maximum of 30 meters horizontally--impressive for a snake, although far less than the distances traversed by at least one well studied close relative, C. paradisi, which is also better able to maneuver while in flight than is C. ornata (Socha and LaBarbera 2005 and references therein).
Socha and Sidor (2005) report on two separate occasions during which C. ornata were observed tracking the movement of a bird and an airplane flying overhead. They suggest that birds may be important predators of these snakes and predict that investigation of Chrysopelea vision will reveal morphological features, such as retinal foveae, that are associated with greater visual acuity.
For a detailed analysis of gliding in C. paradisi (a close relative of the Golden Tree Snake), see Socha et al. (2010) (which also includes several striking images of other gliding vertebrates). For more information on flying snakes, see http://www.flyingsnake.org/ (although not recently updated) and for additional video of flying snakes in action, see here.
