Abstract

Acoustic signals are widely used by animals for communication and the regulation of interactions. Moreover, some acoustic parameters of animal vocalisations have been shown to reliably indicate male quality and play a role in mate and rival assessment. For example, in some deer species, formant frequencies act as cues to body size, and lower formant values and spacing are selected by females in a mate choice context. Reindeer possess a peculiar vocal tract anatomy involving a laryngeal air sac which probably acts as an additional filter, making it a candidate species for novel investigations in the field of bioacoustics. We investigated whether some acoustic parameters were good indicators of age and body weight (used as an index for body size). We did this by performing acoustic analyses using recordings collected from a semi-domesticated reindeer population in northern Finland. This study first highlights the complexity of acoustic parameter extraction from reindeer male vocalisations, likely due to the presence of the laryngeal air sac. We found age of subadult males (aged 2.5-4.5 years) to be negatively correlated with formant F3 and formant spacing, suggesting that their vocalisations convey information on the caller’s age. Formant frequencies were not affected by male body weight, suggesting they may not provide information on male size in our population. In contrast, we found that heavier males had a lower formant spacing. It is thus probably a key acoustic parameter in mate and rival assessment as it gives an honest indication on male body weight. We discuss the importance of reliable acoustic cues to size and quality indices in sexual selection contexts. However, it is highly likely that reindeer males and females rely on other signals as well, such as visual and olfactory cues, to gain information on male attributes. We suggest that further investigation is needed to better understand how the laryngeal air sac affects vocal production.