The researchers developed a theory: Perhaps the snakes’ sudden, high-frequency chatter created an illusion of proximity that acts as a warning. dr. Chagnaud first wanted to test this theory on buffalo at the Munich Zoo before realizing it would be much easier to use students, who are generally more willing subjects.
The volunteers sat on a chair in the middle of a room and wore a virtual reality headset that moved them through a grassland to a hidden snake at dusk. As the rattles increased in frequency, the volunteers pressed a button to indicate when they thought they were about three feet from the snake. All subjects pressed the button as the chatter jumped in frequency, misinterpreting their actual distance.
The researchers propose that this sudden jump in frequency is an evolved behavior that rattlesnakes use to fool the listener about their actual distance from the snake. “The shift in the rattling is a subterfuge on the part of the snake,” said Bruce Young, an anatomist at the Kirksville College of Osteopathic Medicine in Missouri, who reviewed the article.
However, calling this subterfuge is just one hypothesis, clarified Dr. chagnad. In another explanation, the rapid chatter could be a strategy to grab the listener’s attention, similar to provoking a startle response, such as when a loud noise makes a person flinch. But dr. Chagnaud points out that a snake can more efficiently trigger a startle response by jumping from 3 hertz to 100 hertz; he believes the slow rattling rise to 100 hertz is better explained by an illusion of proximity.
But humans were never the intended evolutionary target of a rattlesnake, as the snakes have been roaming North America for at least six million years. dr. Rowe said the paper didn’t necessarily clarify how the animals that evolved along with the rattlesnakes, such as badgers or canids, perceive the rattle.
Unfortunately, doing the same virtual reality experiment on a marten-like would probably be chaotic and stressful. “Can you put glasses on a tie?” dr. Rowe wondered aloud. “Bags are so stubbornly unmanageable.” In his view, California ground squirrels would be a rattlesnake enemy much better suited to virtual reality.
“There are a lot of smart young scientists out there who might be able to figure out a way to get a squirrel to sit in front of a monitor with a pair of tiny headphones,” said Dr. Rowe.