ALLOMETRIC SCALING AND INTERSPECIFIC DIFFERENCES IN THE RATTLING SOUNDS OF RATTLESNAKES

Rattlesnakes produce sounds by shaking a unique appendage at the tip o f their tail called a rattle. The rattle is generally assumed to funct ion as a warning to enemies about the rattlesnake's venomousness. Neve rtheless, rattle size varies among species, perhaps as a result of gen etic drift, natural selection, or allometry. Quantitative analyses of rattling, appropriately scaled to species' differences in body size, w ere used to examine interspecific differences in rattle structure a an d function. We recorded, digitized, and analyzed rattling sounds of 19 4 individuals of 21 different species. Although ANOVA results indicate d that rattling sounds differ significantly across species, removal of interspecific differences in SVL through ANCOVA resulted in rattling sounds that were statistically indistinguishable among all species exc ept the pigmy rattlesnake, Sistrurus miliarius. Even when adjusted for its small body size, the pigmy rattlesnake has a significantly quiete r and higher pitched rattle than most other species tested. The atypic al rattling of S. miliarius is related to the disproportionately small rattle of this species. Regression analyses indicated that rattle siz e is the best predictor of all acoustic descriptors of the rattling so und. When the influences of interspecific differences in rattle size w ere removed via ANCOVA, rattling sounds were statistically similar amo ng all species of rattlesnakes, including S. miliarius.