 In a study of the rattling made by rattlesnakes of different species , the Canadian zoologists Brock Fenton and Lawrence Licht found that the sounds are always similar : they have rapid onset ( starting suddenly , and reaching full volume in a few milliseconds ) ; they consist of a ' broadband ' mixture of frequencies between 2 kHz and 20 kHz , with little energy either in the ultrasonic ( above 20 kHz ) or in the rattlesnakes ' hearing range ( below 700 Hz ) ; and the frequencies do not change much with time ( the rattling after 2 minutes having a similar spectrum to that at onset ) . There was no clear difference in the sounds made by the different species measured : Crotalus horridus , Crotalus adamanteus , Crotalus atrox , Crotalus cerastes , Crotalus viridis and Sistrurus catenatus . This pattern implies that the rattling " could serve as a general attention @-@ getting device " , which " is designed as a deimatic or startle display " . Its similarity to the " broadband , harsh sounds " used as warning calls by birds and mammals may enhance its effectiveness . Since rattlesnakes can barely hear the sound , it is unlikely to serve as any form of communication to other snakes of the same species . Finally , the sounds are not in themselves loud enough to cause pain and hence keep predators away . 
