Vocal individuality in cohesion calls of giant otters, Pteronura brasiliensis

Social calls conveying identity yield several advantages in managing social group living. Signalling identity to conspecifics and the perception of the calling individual by receivers allow for appropriate behavioural responses based on experience of previous interactions. Contact calls help maintain group cohesion and often provide individual signatures. Giant otters, endemic to Amazonian rainforests and wetlands, are a highly social and vocally active species. Their family groups consist of a monogamous alpha pair with offspring of different ages, and elder siblings assist in rearing the young. During collective fishing bouts, individuals frequently become separated from their group. Giant otters use two types of cohesion calls. The 'contact call' is often uttered when the otters are visually separated, and is then followed by the reunion of group members. The 'hum' is produced in close proximity to manage group movements. We predicted giant otters would have individually distinct cohesion calls and be able to discriminate between the cohesion calls of different individuals. We recorded and measured calls from wild and captive individuals and conducted habituation-dishabituation playbacks with two captive groups. Our results provided statistical evidence for a strong individual signature in contact calls but not in hums. Nevertheless, the giant otters were able to distinguish individuals in both cohesion calls tested. We conclude that individual signatures seem to be advantageous in terms of managing group movements. Giant otters might additionally benefit from discriminating individuals within their social group, where kin recognition is insufficient to identify equally related individuals that cooperate in hunting and rearing of the young.