Are you talking to me? Captive Asian elephants react to voice familiarity and Elephant-Directed speech

Recent studies on the socio-cognitive abilities of animals, including elephants, have highlighted their aptitude to perceive and respond to human cues, particularly in captive settings. These abilities are crucial for fostering positive interspecies relationships and improving animal welfare in zoos. Previous research has shown that Asian elephants (Elephas maximus) can distinguish between familiar and unfamiliar humans through various sensory cues, such as visual and olfactory signals. Additionally, familiarity with caregivers reduces elephants' stress and has been linked to more cooperative behaviour and better task performance, highlighting its importance for the management and welfare of animals under human care. Yet the role of vocal communication in shaping these effects remains poorly understood, and less is known about how the type of speech caregivers use might affect elephants' behaviour. In the present study, we investigated how captive Asian elephants react to keepers' voices, focusing on the effects of voice familiarity, speech type and the interaction between the two variables on their behavioural response. We played recorded stimuli of familiar and unfamiliar voices speaking in either Elephant-Directed Speech (EDS), characterised by a high pitch and varied intonation, or Adult-Directed Speech (ADS), which does not present these acoustic characteristics. Our data show that vocal stimuli of any kind increased elephant arousal. Moreover, the elephants turned their bodies towards the doors used by the keepers - which we interpreted as behaviour indicative of a search for the keeper - when listening to EDS compared to ADS, or when the voice was uttered by a familiar rather than an unfamiliar keeper. However, no significant differences were found for the interaction between the speech type and familiarity for the duration of any behaviour analysed. Additionally, elephants engaged in aggressive displays more rapidly in response to ADS than to EDS, and initiated search-for-keeper behaviour significantly faster when exposed to EDS from a familiar keeper compared to EDS from an unfamiliar keeper. Overall, our results suggest that elephants can distinguish between familiar and unfamiliar voices and between two types of speech register with different acoustic features and therefore respond differently. Our work opens a window on the cognitive skills of the elephants.