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Rattlesnakes, masters of fatal deception

A rattlesnake manipulates its rattle sound to deceive its predators to think that its closer to them than they actually are (Pic. Courtesy wikimedia commons)

Imagine a siren or beep sound becoming louder in order to alert a person about the approaching danger. That is what a rattlesnake does when approached by humans except for one crucial aspect. It alters the frequency of its rattles to trick its predators, including humans by making them think that they are closer to the reptile than they actually are.

This was found by a group of scientists who published their findings in Current Biology, according to an article in smithsonianmag.com.

Sharing details about this study in a Press release, its co-author, Boris Chagnaud said: “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.”

Chagnaud is a biologist at Karl-Franzens-University Graz in Austria.

Giving an apt example of this change in rattle frequency, he compared it to the beep of a reversing vehicle, which became louder and faster, as it approached an object.

For a very long time it was known that the reptile uses its rattle to provide an indication of its presence in the vicinity but their use of varied rattle frequencies was less understood till now. Interestingly, the rattles are hollow structures which are made of keratin – the material of which human fingernails are made of.

The idea of doing this study came when Chagnaud realised that the rattlesnake housed in an animal care facility would rattle faster when he approached the creature. This made him think if this rattle frequency was a message or signal to those around the reptile. He told the New York Times the message was: “Hey. I’m sitting here. Don’t step on me because I’m going to bite you.”

In order to understand this, experiments were designed in which the western diamondback rattlesnake was approached by an object which included a humanlike torso and large black disk. It was found that the snake’s low-frequency rattle, which was around 40 hertz, moved to 70 hertz. The change in the frequency — that is to a faster one — changed according to the individual.

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Further, the team sent into a virtual reality grassland 11 people. This grassland was full of hidden snakes. Participants were able to guess the snake’s distance with reasonable accuracy when the rattle was of lower frequency. Then, when they came within four meters of the serpents, the rattle frequency increased. When participants were asked to press a button when they thought they were one meter away from a virtual snake, they consistently underestimated the distance.

In a Press release Chagnaud stated: "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."

Giving the reason as to why this happens, Jason Bittel of National Geographic said, the higher frequency rattles seem closer to humans due to a sound-perception quirk. Making the individual rattle sounds blend into one note, makes it seem louder.

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Whit Gibbons, herpetologist, who was not part of the study observed: "Like other snakes, rattlesnakes, of which there are numerous species in North America, are more interested in being undetected than confronting any other animal other than their prey.”

Deception has worked wonders for the rattlesnakes for millions of years, helping them to keep predators at bay!