<P> The speed of tail vibration is directly correlated with temperature, at least for rattlesnakes . The warmer a rattlesnake, the faster it vibrates its tail . Rattlesnakes tail - vibrate faster than other snakes, with some individuals nearing or exceeding 90 rattles per second . This makes rattlesnake tail vibration one of the fastest sustained vertebrate movements--faster than the wingbeat of a hummingbird . The movement is possible thanks to specialized "shaker" muscles in the rattlesnake tail . </P> <P> Snakes more closely related to rattlesnakes vibrate more quickly than do more distant rattlesnake relatives . In one study that measured tail vibration in 155 snakes representing 56 species, vibratory speed ranged from 9 vibrations per second (Bothriopsis taeniata) to 91 rattles per second (Crotalus polystictus). In the study, only two rattlesnakes (of 33 individuals filmed) had a maximum vibratory rate slower than the fastest non-rattlesnakes . The fastest non-rattlesnakes examined were species of Agkistrodon and New World Colubrids, both of which could sustain vibratory speeds up to about 50 rattles per second . </P> <P> It is unknown what benefit a snake derives from such fast speeds of tail vibration . One study did find that ground squirrels, Spermophilus beecheyi, are able to ascertain the threat level posed by a rattlesnake based on its rattling speed . Thus, it is possible that fast rattling speeds could be driven by predator - mediated selection, whereby snake predators avoid faster - vibrating individuals . </P> <P> It is also unknown what the specific function of tail vibration is . Many researchers have posited that it is primarily an auditory aposematic warning signal--like the growling of a wolf or the sound associated with African whistling thorn acacia (Acacia drepanolobium). Others have suggested it could serve as a distraction--particularly for nonvenomous species--meant to draw attention away from a snake's head and towards its less vulnerable tail . </P>

Snake that shakes its tail like a rattlesnake