Investigating context-specific acoustic variation in the bleats of male domestic sheep.

Abstract

Vocalizations provide an informative means of assessing the emotional states of animals, yet male vocal behaviour in domestic sheep remains unexplored. The study aimed to investigate whether rams' bleats vary across five distinct contexts associated with morning and night isolation, exposure to familiar ewe-bell sounds, feed anticipation, and feed denial. A total of 428 high-quality bleats were used to extract 20 acoustic parameters, which were then analyzed using a multivariate acoustic approach. Principal Component Analysis identified five independent acoustic components reflecting source-parameters, spectral energy, formant frequencies, voice stability, and temporal characteristics. Context significantly influenced the acoustic structure of bleats, with spectral, formant, vocal stability, and temporal characteristics showing context-dependent variation, whereas fundamental frequency-related parameters remained unaffected. Feed anticipation elicited higher formant-related scores; feed denial produced reduced spectral energy, and social isolation contexts were characterized by increased vocal instability. Discriminant analyses revealed moderate classification accuracy, indicating overlapping acoustic patterns and supporting graded rather than discrete vocal signals. Morphometric effects were minimal, with wither height affecting formant structure. The findings provide the first detailed evidence that rams modulate multiple acoustic features across contexts, demonstrating that male sheep encode emotional states through shifts in vocal parameter variation.