New Snake Footage Uncoils Mystery of Flying Serpents
for National Geographic News
|August 7, 2002|
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Watch outthere's a snake flying through the air!
No, it's not a paranoid hallucination. Along the west coast of India and in parts of Southeast Asia and Sri Lanka, some snakes slither through the jungle, bite with venom, and glide from tree to tree.
"How does a long cylinder with no appendages move through the air?" asked Jake Socha, a biologist at the University of Chicago in Illinois. "How is it able to turn? Why doesn't it tumble over in the air?"
To help answer these questions, Socha created a three-dimensional reconstruction of the snakes' flight using digital video cameras and computer software normally used to analyze aerial and satellite photos.
Reporting his preliminary findings in the August 8 issue of Nature, Socha said his research shows that the snakes flatten and undulate their bodies to glide through the air. Undulation is key to their ability to stay aloft, he said.
"The undulation is not akin to a flapping wing," Socha explained. "It's more like putting a whip on a large table and then moving the whip from side to side, with waves moving down the whip."
Michael LaBarbera, Socha's Ph.D. thesis adviser at the University of Chicago, praised Socha's work. "No other study on any other gliding animal has reconstructed the flight in this detail," he said, adding: "Jake has set a new standard of excellence for other workers in animal aerodynamics."
There are five species of flying snakes, all of the genus Chrysopelea. Adults average about three feet (one meter) long, and though not lethal, some have a pretty testy temperament, said Socha.
"They do have small fangs in the back of their mouth and inject a small amount of venom when they eat, but they're harmless to humans," he said. "I've been bitten many times with no effect."
No ecological studies have been conducted to determine why these snakes take to the air. Socha speculates that they employ gliding flight as a means to get around the forest more efficiently, and possibly to aid in catching prey such as lizards, birds, and bats.
Like more familiar gliders, such as flying squirrels, flying snakes are not actually able to fly upward. Their flight is actually the ability to glide considerable distances from the high branches of trees.
Socha's research took him to the Singapore Zoological Gardens, where he teamed up with Tony O'Dempsey, a snake enthusiast and an expert in calculating measurements from photographs (photogrammetry). They created stereo movies of the snakes in flight.
O'Dempsey works for Environmental Systems Research Institute, a geographic information system (GIS) software company. He learned about Socha's research through an e-mail appeal for volunteers.
"He helped me set up a system so that I could reconstruct the 3-D coordinates of the snake throughout its trajectory by placing two digital video cameras on the top of the tower that the snakes jumped from," said Socha.
The research method was based on standard practices used in the GIS industry to make maps from aerial photographs. "The principle of photogrammetry is that stereo imagery is acquiredthat is, images taken from two or more vantage points," said O'Dempsey.
In his study, Socha marked snakes at three points on their bodieshead, midpoint, and ventand tracked them through courses of flight to determine their position, posture, and speed. A computer model combined the multiple images to render the snake's aerial position in three dimensions.
"The snakes' aerial behavior is radically dynamic for a glider," said Socha, who described the flight in his report in Nature.
A flying snake begins its takeoff by hanging from a branch with the front of its body forming a J-shaped loop. It then accelerates up and away from the branch, straightening the body and flattening it from head to tail end, so that the body width nearly doubles.
As the snake gains speed, it lifts its head and tail end toward the middle and undulates from side to side in a wide S shape. The snake generates lift, said Socha, although he is not certain how it's done.
"This combination of movement and postural regulation is not known to occur together in any other snake and likely requires specialized neuromuscular control," he concluded in his scientific paper.
LaBarbera said the phenomenon is so unique it warrants further study.
"I think its likely that this is the one and only time in the history of the planet that an animal without appendages achieved flight," he said. "We are privileged to be here to appreciate it and to try and understand just how they manage to pull the trick off."
The next phase of Socha's research, which is funded in part by a grant from the National Geographic Society's Committee for Research and Exploration, will involve experiments to determine which features of behavior and body shape enable the snakes to glide.
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