GRAZ, Austria — Rattlesnakes shake louder to make listeners think they are closer than they actually are, reveals a new study. The venomous predator uses the tactic as a warning to other animals, and can trick the ear into believing they are right beside the snake.
Researchers from Karl-Franzens-University-Graz in Austria made the observation when, during a visit to an animal facility, the rattling increased in frequency when rattlesnakes were approached but decreased when walking away. They experimented by having a human-like torso move towards the snake, showing the rattling rate increased from approximately 40 Hz to a higher frequency between 60 and 100 Hz.
Additional results showed rattlesnakes adapt their rattling rate in response to the approach velocity of an object rather than its size.
“Our data show that the acoustic display of rattlesnakes, which has been interpreted for decades as a simple acoustic warning signal about the presence of the snake, is in fact a far more intricate interspecies communication signal,” explains senior author Boris Chagnaud in a statement. “The sudden switch to the high-frequency mode acts as a smart signal fooling the listener about its actual distance to the sound source. The misinterpretation of distance by the listener thereby creates a distance safety margin.”
“In real life, rattlesnakes make use of additional vibrational and infrared signals to detect approaching mammals, so we would expect the rattling responses to be even more robust,” says Chagnaud. “Snakes do not just rattle to advertise their presence, but they evolved an innovative solution: a sonic distance warning device similar to the one included in cars while driving backwards.
“Evolution is a random process, and what we might interpret from today’s perspective as elegant design is in fact the outcome of thousands of trials of snakes encountering large mammals,” he continues. “The snake rattling co-evolved with mammalian auditory perception by trial and error, leaving those snakes that were best able to avoid being stepped on.”
South West News Service writer Tom Campbell contributed to this report.