Evidence of two types of coordinated vocalizations used in different territorial defence contexts by an Asian cooperative breeder

Avian vocal systems serve different functions depending on context. Cooperative breeders have more complex communication systems than pair-breeding species due to their relatively complex social systems, but we still have a limited knowledge of these, especially in species producing coordinated vocalizations. In addition, it is unclear if coordinated vocalizations can be context-dependent in passerine species. Here, we describe for the first time the vocal system of an Asian cooperative breeder, the Masked Laughingthrush Pterorhinus perspicillatus, and test if this species uses different duets in different territory defence contexts. Based on 789 vocalizations from 23 groups, we found that Masked Laughingthrushes produced complex vocal repertoires containing at least 11 vocalization types, including eight typical call types, three duet types, and one chorus. Typical calls served cohesion, vigilance, and begging functions. According to playback experiments, the groups responded to solos and duets with equal strength, and most group members approached the loudspeaker together, which suggested that the type 1 duet functioned as territorial defence. More importantly, we found that one duet type (type 1 duet) was used in the absence of neighbors during territory advertisement, while another type (type 2 duet) was elicited during encounters with other groups. Our study unveiled that the Masked Laughingthrush appears to be the first passerine species reported to use distinct duet types for different territory defence contexts.