Acoustic features indicate arousal in infant giant panda vocalisations

Infant giant pandas are highly vocal during the first few weeks of life, producing vocalisations that are characterised by noisy, aperiodic segments. The aperiodic character of many animal vocalisations results from irregular vibratory regimes of the vocal folds, and one proposed function of this so-called nonlinear phenomena (NLP) in animal vocalisations is to convey information about the caller's arousal state. This hypothesis was tested in the vocalisations of six hand-reared giant panda cubs recorded during handling and feeding procedures that had been categorised into low- and high-arousal contexts based on quantified motor activity. Ninety-three per cent of the vocalisations contained NLP, including deterministic chaos and subharmonics. Vocalisations produced in the high-arousal contexts, however, were characterised by an increase in chaos, as well as increased call duration and x¯ fundamental frequency (pitch). These results suggest that infant giant panda vocal signals have the potential to express different arousal states. Furthermore, because giant panda cubs are the smallest placental mammal offspring at birth compared with adult size, acoustically conveying arousal state to the mother might be crucial for infant survival under natural rearing conditions