What do rattle quills tell? A morphological analysis of the rattling in the African crested porcupine

Sonations are non-vocal acoustic signals whose production mechanisms have been rarely investigated in mammals. Since sonations are directly tied to specific anatomical characteristics, one issue in acoustic communication studies is estimating the morphological diversity of the structures responsible of sound emission. The nocturnal and social habits of the African crested porcupine make them an ideal model to address this issue. Both sexes bear highly specialised quills on their tail that, by colliding against each other, produce a sound (rattling). We measured the quills of 130 subjects and found that their morphology did not vary in relation to season and sex. Compared to subadults (N = 39) and adults (N = 81), cubs (< 6 months, N = 10) have fewer and stubbier rattle quills that also differ in their length and diameter across the age classes. The passage from the cub to the subadult phase seems to sign the most important changes in the quill development. Although it is unknown when and how often a cub produces rattling, the presence of quills at a very early stage of life indicates that they can potentially be used. Although several hypotheses can explain the potential role of cub rattling, one of the most reasonable is that, when olfactory and/or visual contacts are prevented, this sound can alert adults about potential predation risks on offspring. Matching morphological and acoustic data under different contexts will allow understanding the correlates at the basis of the potential roles of such a peculiar way of communication.