VOCAL COMMUNICATION IN THE PALE-WINGED TRUMPETER (PSOPHIA LEUCOPTERA): REPERTOIRE, CONTEXT AND FUNCTIONAL REFERENCE
Adult pale-winged trumpeters produce a varied repertoire of vocalizations: apart from one loud 'tremolo song' we recorded 11 structurally discrete close-range calls, one of which (the 'mew') was individually distinct. There was significant variation across vocalization type with respect to the identity and behaviour of the caller and the response of the receiver(s). It was possible to group vocalizations into six broad contextual classes: alarm, recruitment, social, contact, feeding and territory defence. On detection of danger, trumpeters gave two acoustically different calls, one for aerial predators, and another for terrestrial predators or conspecific intruders. They also produced distinct calls on detection of large prey items such as snakes. These (alarm and snake-finding) call types seemed to evoke different responses by receivers and therefore appeared to be functionally referent. Vocal behaviour was positively correlated with dominance rank and at least two other calls had important roles in mediating social interactions within the group. Finally, the 'mew' call was only given when a trumpeter was separated from, and usually out of visual contact with the rest of the group. This call was functionally referent, eliciting a vocal response from receivers: they produced a loud 'grunt' call, which was also unique to this situation. This is the first experimental demonstration in a bird of the proximate factors motivating production of an individually distinct contact call.