[7][8] This makes rattlesnake tail vibration one of the fastest sustained vertebrate movements—faster than the wingbeat of a hummingbird.
[1] 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.
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.
[9] Thus, it is possible that fast rattling speeds could be driven by predator-mediated selection, whereby snake predators avoid faster-vibrating individuals.
[11] 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.
Proponents of this hypothesis suggest that a proto-rattle may have enhanced caudal luring, a behavior common to rattlesnakes and their closest relatives,[1] because such a structure might have looked similar to an arthropod head.
[15] Those in support of this hypothesis also point out that specialized keratinized structures have evolved in caudal luring species before, such as in the spider-tailed horned viper, Pseudocerastes urarachnoides.