Investigating the aposematic purpose of the rattlesnake rattle

Fowler, John Henry

johnhen@g.clemson.edu

Parkinson, Christopher L.  

Department of Biological Sciences                                                                                                                

Clemson University                                                                                                                                      

Clemson, South Carolina USA

The rattlesnake rattle, a complex sound-producing structure found in the genera Sistrurus and Crotalus, is an evolutionary novelty that enables these snakes to produce a distinctive buzzing sound. This adaptation is believed to have facilitated the diversification of rattlesnakes into over 50 species. Despite its widespread recognition, the effectiveness of rattling as a deterrent and the specific animal taxa most impacted by it remain poorly understood. While it has long been hypothesized that rattling deters predators and prevents trampling by large herbivores, strong scientific evidence supporting these claims is lacking. Additionally, the assumption that rattling is a more effective deterrent than the basal hissing sound produced by many snakes has not been adequately tested. To investigate these hypotheses, we conducted field studies using automated behavioral response systems (ABRs) to assess the effectiveness of rattling compared to hissing. We assembled ABRs using FreakLabs Boombox sound systems with speakers and high-quality game cameras. The Arduino circuit board in the Boombox was programmed to randomly play specific preloaded sounds when triggered by the camera motion detectors, following a three-second delay. We used an ethogram to assess the behavioral responses of various South Carolina vertebrates, including ungulates, mesocarnivores, and birds. Our preliminary analyses suggest that both hissing and rattling are similarly effective at eliciting fear responses in wild animals and are nearly as effective as human sounds in causing flee responses. These findings provide new insights into the use of the rattlesnake rattle and its effectiveness as a deterrent.