In long-range fission-fusion complex societies, individuals are often recognized by audiovocal signals because of long-range propagation. The signature voice system is a well-known mechanism involving both acoustic individuality of a certain call type and discrimination ability. Previous studies on vocal individual recognition of birds have emphasized its involvement in breeding contexts such as mate, parent and offspring, and territorial-neighbour recognition. However, there has been less focus on the recognition of non-breeding flock members despite the socio-ecological demand of such ability in the complex social lives of highly social birds including corvids. Here we report a signature voice system in jungle crows by showing both acoustic individuality of contact calls and discrimination ability. We first performed a discriminant functional analysis on contact ka calls of five crows to examine their discriminatory potential and demonstrate inter-individual distinctions. We next used an operant conditioning to verify the perceptual ability to discriminate non-breeding familiar conspecifics based on ka calls. Four of the five crows successfully transferred discrimination of individual calls to the novel ka calls. Our results provide the first evidence of a signature voice system as a perceptual mechanism for individual recognition of familiar individuals in non-breeding flocks of a highly social crow.
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