Decoding parrot duets: Complex communication in yellow-naped amazons

Parrots represent an excellent model in which to study complex vocal communication because they meet the prerequisites of the social complexity hypothesis and, like humans, have lifelong vocal learning. Despite that, the difficulty in acquiring good field data on wild parrot vocalizations has limited such research. Here, we examine the warble duets of the yellow-naped amazon, a critically endangered species, which are used by mated pairs when defending territories. We found that these duets are marked by a large lexicon of 36 call types, with additional variants. The calls also assort non-randomly within the duets and are organized by syntactic rules. In addition, 58% of call types were sex specific, while the remaining call types were used by both sexes and thus appeared to be sex-neutral. Overall, the duets were marked by great variability; despite being structured by syntactic rules, we observed very little overt repetition in entire duets. This research provides important evidence that large repertoires and complex vocal communication are an important part of the natural communication systems of wild parrots.