Researchers have discovered that the rattling produced by rattlesnakes is more complex than it was believed before. It appears that the snakes switch to a higher frequency in order to fool any threats, tricking them into thinking they are closer than they are, in fact.
“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. 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,” explained author Boris Chagnaud.
The study began from a simple observation. Chagnaud observed that the frequency of rattling decreased when he distanced himself from the snakes, but the frequency increased when he got closer. A series of experiments showed that snaked abruptly changed to a higher frequency when potential threats approached, going from 40 Hz to 60 up to 100 Hz. This change of frequency tricks those around them into believing the snakes are closer than they actually are. When testing this with 11 participants, all of them were fooled by the rattling frequency.
“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 backward. 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,” Chagnaud added.