Horse whinnies: a source of social information
For animals living in social groups, like horses, it is known that they regularly interact with other animals. Frequently these signals are vocal, for horses this is whinnying. In other species such calls can contain information about: species, sex, kinship, emotional state, hierarchical status and social bonding.
Horses are known to display a large range of visual signals and are known to be visual communicants, with small vocal repertoires. However, they also use long-distance whinny calls to maintain contact. Little is known about the information hidden in these calls in horses. The aim of this study was to investigate the potential existence of individual acoustic signatures in whinnies of horses and the ability to discriminate individuals from these calls based on their degree of familiarity.
The study was executed by recording on average 16 whinnies per horse for 30 horses, across multiple days for each individual. Each subject was isolated from its stall or pasture before recording, as whinnies are often produced in social context. The recordings were played back to 12 horses and classified under: group whinnies, familiar whinnies, unfamiliar whinnies and a control with white noise.
The results show that some of the frequency and temporal parameters carry reliable information about the caller’s sex, body size and identity. Not only did the horses discriminate the social category of the caller but also reacted with sound-specific behaviour. No correlations with age were found and the control sounds did not induce any particular response.
Expert opinion by Anouk van Breukelen
These results provide more insight into the perception of the social world in horses. Further research on a larger group of horses is required to confirm the results and to get more insight in the vocal coding/ decoding processes of (social) information in horses.
> From: Lemasson et al., Animal Cognition 12 (2009) 693-704. All rights reserved to Springer-Verlag. Click here for the online summary.