Behaviour and Social Vocalisation During Aerial Flocking of the Black-nest Swiftlet (Aerodramus maximus) in Sarawak, Malaysia

Black-nest Swiftlet, Aerodramus maximus, is one of the most studied Bornean avian species that possesses several unique features in term of its morphology (inconspicuous plumage colouration, monomorphic and cryptic to a few other sympatric species), extreme aerial lifestyle and cave dwelling habit. This study explored the communication system of this gregarious and communal species by reviewing its communication signals (displays) during aerial flocking. Field observation and sound recording were conducted at two study sites in Sarawak, Bau and Bukit Sarang, Bintulu. Based on the observation data, the overall flocking condition was described and an ethogram of aerial behaviour, including both visual and acoustic displays was constructed. Meanwhile, the vocalisation samples (acoustic display) were first classified into vocal types and categories through perceptual classification to build up the vocal repertoire of this species, each type was further characterised with sound structure measurements and the measurement data were analyzed statistically to recheck the initial vocal classification, the statistical test applied are Kruskal Wallis Test, Principle Component Analysis (PCA) and Discriminant Function Analysis (DFA). Selected vocal samples with aerial display types noted were also examined to check the association between vocal types and aerial display types. The flocking activity condition of this species was found to be highly varied from day to day. There were 16 aerial behaviour types recorded under four categories: locomotion, individual display, group display and vocal behaviour. While three vocal categories, including one type of Rattle Call, five types of Scream Call and two types of Chirp Calls, were discovered. Number of Note (NON) was recorded and 12 temporal and frequency parameters were measured for each of the types, the measured parameters that is efficient in separating vocal categories are Duration of First Note (DFN), Duration of Last Note (DLN) and Time Interval between the Second Last and the Last Note (TSL). Another two new findings from the ocalisation study are the existence of triple, quadruple and pentuple click designs in Rattl