Camel whistling vocalisations: male and female call structure and context in Camelus bactrianus and Camelus dromedarius

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.

KEYWORDS:

• Artiodactyla
• Camelus bactrianus
• Camelus dromedarius
• sex differences
• high-frequency calls
• ruminant
• rutting vocalisation
• whistle mechanism

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

Audio and video files supporting this article have been uploaded as supplementary material.

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

Supplemental data for this article can be accessed here.

Additional information

Funding

This study was supported by the Russian Science Foundation (grant number 19-14-00037).