Turns out snakes are even sneakier than you might have thought. Well, at least rattlesnakes are.
A new study from Austria’s Karl-Franzens-University Graz has revealed that the reptiles increase the frequency of their rattles to trick people into thinking they’re closer than they actually are.
This auditory illusion evolved to warn others of their presence and avoid being trampled on, researchers believe.
“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,” said senior author Prof Boris Chagnaud at Karl-Franzens-University Graz.
“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.”
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By pushing a human-like dummy slowly towards a western diamondback rattlesnake in a lab setting, scientists recorded how its rattling rate increased from 40 rattles per second, to 60–100 as objects reached four meters away.
The snake’s rattle is create by the shaking of hard rings of keratin – the same material that makes your fingernails – at the end of its tail.
The researchers also discovered that the snakes adapted their rattling rate when the dummy moved faster towards them. “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,” Chagnaud explained.
In a further experiment, researchers asked humans to approach a hidden sound source that replicated the same change in rattle frequency. Asked to guess when the speaker was one meter away, the majority of participants underestimated their distance to the replica rattlesnake.
“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,” Chagnaud concluded.
“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. 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.”
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