How many ways can a snake growl? The morphology of sound production in Ptyas mucosus and its potential mimicry of Ophiophagus

As part of its defensive display the Indian rat snake, Ptyas mucosus, medio laterally compresses the anterior portion of its body and expands its throa t region ventrally. During this postural display P. mucosus produces a deep , rumbling defensive growl. Acoustic analysis of this growl revealed it to be a long moderately loud sound dominated by lower frequencies. Binding the neck and anterior portion of the body with surgical tape prevented the pos tural display; while the defensive sounds produced by bound specimens had t he same duration and amplitude, their frequency increased significantly. Th e tracheal membrane of P. mucosus is unusually wide and expands away from t he tracheal rings into the body cavity. We hypothesize that during the defe nsive postural display the expansive tracheal membrane is collapsed forming isolated pockets which have a resonance effect on the exhalent airstream. Ptyas mucosus may be an acoustic Batesian mimic of the king cobra, Ophiopha gus hannah.