Horse (Equus caballus) whinnies: a source of social information |
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Authors: | Alban Lemasson Anaïs Boutin Sarah Boivin Catherine Blois-Heulin Martine Hausberger |
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Institution: | 1. Université de Rennes 1, EthoS ?Ethologie animale et humaine?, UMR 6552, C.N.R.S., Station Biologique de Paimpont, 35380, Paimpont, France
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Abstract: | Many animal species that rely mainly on calls to communicate produce individual acoustic structures, but we wondered whether
individuals of species better known as visual communicants, with small vocal repertoires, would also exhibit individual distinctiveness
in calls. Moreover, theoretical advances concerning the evolution of social intelligence are usually based on primate species
data, but relatively little is known about the social cognitive capacities of non-primate mammals. However, some non-primate
species demonstrate auditory recognition of social categories and possess mental representation of their social network. Horses
(Equus caballus) form stable social networks and although they display a large range of visual signals, they also use long-distance whinny
calls to maintain contact. Here, we investigated the potential existence of individual acoustic signatures in whinny calls
and the ability of horses to discriminate by ear individuals varying in their degree of familiarity. Our analysis of the acoustic
structure of whinnies of 30 adult domestic horses (ten stallions, ten geldings, ten mares) revealed that some of the frequency
and temporal parameters carried reliable information about the caller’s sex, body size and identity. However, no correlations
with age were found. Playback experiments evaluated the behavioural significance of this variability. Twelve horses heard
either control white noise or whinnies emitted by group members, familiar neighbours or unfamiliar horses. While control sounds
did not induce any particular response, horses discriminated the social category of the callers and reacted with a sound-specific
behaviour (vigilance and attraction varied with familiarity). Our results support the existence of social knowledge in horses
and suggest a process of vocal coding/decoding of information. |
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Keywords: | Individual acoustic signature Auditory recognition Body size Sex difference Social familiarity Domestic horse |
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