European biologists called the rattle an analogue of the parking assistance system: it warns not only about the presence of a rattlesnake, but also about the distance to it, and does it wrong.
Poisonous cousins of vipers - pit viper snakes - are distinguished by a pair of additional pits between the eyes and nostrils, which are sensitive to temperature. These include the North American rattlesnakes, armed with a scaly rattle that emits a characteristic sound when the reptile twitches its tail threateningly. The frequency of this sound changes as the animal approaches the snake, which makes it deceive, more frightened than it should be. This is the conclusion reached by biologists from Germany and Austria, whose article was published in the journal Current Biology.
"Our data suggests that the acoustic signals of rattlesnakes, which have always been considered a simple warning of their presence, serve as a more sophisticated means of interspecies communication," says lead author Boris Chagnaud. "The abrupt transition to higher frequencies deceives the listener, disrupting the perception of distance to the snake and creating a wider safe space around it."
Initially, Shano and his colleagues noticed an increase in the frequency of the rattle sound as a potential threat approached a snake. Then they conducted experiments in the laboratory, leading a figure in the shape of a human torso to the animals, or using a black disc of varying diameter to simulate convergence by increasing its size. It turned out that the rattlesnake responds precisely to the speed of the object's approach. As the “threat” grew, it increased the frequency of the rattle to 40 hertz, after which it sharply raised it to 60-100 hertz (in most cases, about 70 hertz).
To test the effects of this sound on humans, scientists have developed a virtual environment that simulates contact with a snake in safety. Eleven volunteers wearing VR glasses could see the grassy wasteland in which a snake lurked. When “approaching” her, she made the same thundering sounds, and when a person came closer than four meters, she sharply increased the frequency to 70 hertz.
The participants were asked to stop the experiment when they felt the distance to the virtual snake was one meter. However, an unexpected jump in the frequency of sound forced them to make serious mistakes and stop the approach long before a meter distance. “The snakes are thundering not just to indicate their presence, they have found a more innovative solution: a sound signal, which works like a parking assistance system in a car,” says Boris Shano. "The rattle evolved in parallel to mammalian hearing aids, through trial and error, providing snakes with an excellent signal not to be stepped on."