ABSTRACT
Among ruminants, some species of cervids, bovids and camelids are capable of producing very high-frequency (HF) calls potentially produced by the aerodynamic whistle mechanism. We analysed the HF calls of six individual adult captive camels: three male and one female two-humped Camelus bactrianus and one male and one female one-humped C. dromedarius. Context of emission differed between sexes and individuals. Males of both species vocalised when guarding females during the rut. Females of both species vocalised towards their mates, postpartum (female C. bactrianus) or when protesting against preventing locomotion over enclosure (female C. dromedarius). In either species or sex, the HF calls were faint tonal vocalisations slightly modulated in fundamental frequency (f0). Between species, the calls were significantly lower-frequency (1.7 ± 0.16 kHz) and longer (0.23 ± 0.08 s) in C. bactrianus than in C. dromedarius (3.12 ± 0.11 kHz; 0.16 ± 0.05 s). Nonlinear vocal phenomena (subharmonics and sidebands) occurred in both species but not in all individuals. We discuss the relationship of the f0 of the HF calls with body size and vocal fold length in ruminants. We conclude that the ‘whistling’ HF calls of C. dromedarius are the highest-frequency vocalisations in Artiodactyla.
Acknowledgements
We greatly thank Andrey V. Popov for his valuable help with recordings of male and female C. bactrianus at the Chernogolovka biological station.
Data accessibility
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Disclosure statement
No potential conflict of interest was reported by the authors.
Ethics
All recordings were conducted non-invasively. During our work, we adhered to the ‘Guidelines for the treatment of animals in behavioural research and teaching’ (Anim. Behav., 2020, 159, I-XI). Protocol of recordings for this study was approved by the Committee of Bio-ethics of Lomonosov Moscow State University (research protocol # 2011-36).
Supplementary material
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