Bulbuls are commonly known songbirds distributed in southern Asia and Africa. Most of them are gregarious, industrious, inquisitive, cheery, conspicuous and inhabitants of forests. Twenty species of bulbuls are found in the Indian subcontinent including some endemic and/or rare species. Though some aspects of behavioural ecology and sociobiology of bulbuls were documented in some species, the information on communication systems is scanty. In the present investigation, an effort has been made to characterize and document the vocal repertoire in two sympatric, congeneric species of bulbuls viz. the Red-vented bulbul, Pycnonotus cafer and Himalayan bulbul, P. leucogenys.

Vocalizations of target birds were recorded in their natural habitats, using Marantz PMD 222 sound recorder and Sennheiser ME-66 microphone, during March 2002 to June 2004, in Doon valley (30°26’N; 78°06’E). Behavioural correlates and some playback experiments were used to infer the possible meanings of signals. Acoustical analysis were made using, Avisoft SAS Lab Pro (version 4.23f) with following setting of SAS Lab: 512 FFT-length, Hamming window and >75% time window overlap.  

Both species used their own vocal repertoires composed of different types of acoustic signals, with or with out visual displays. Individuals sang throughout the year and most songs were discrete and stereotyped composed of species-specific phrases. On the basis of acoustical features and context of production, it seems that both species used two categories of songs. Type-A songs were discrete, simple, loud, stereotyped, mostly spontaneous and commonly sung throughout the year, probably to maintain pair bonds. Type-B songs were rare, complex with irregular inter-phrase gaps and low amplitude, mate oriented and most likely used for mating purposes along with mate acquisition/ courtship displays. Territory guarding/ conflict was not seen. Playbacks of songs elicited no response. Individuals allowed conspecifics/heterospecifics in close vicinity. However, mate guarding was observed to be frequent. Different types of context-specific calls were identified. Individuals produced Type-I alarm calls (fast and wide band) under low risk and Type-II calls (loud and narrow band) under high risk. Playbacks of alarm calls suppressed begging calls of nestlings/ fledglings. Roosting calls were very similar to alarm calls Type-I. It seems that roosting calls have evolved from alarm calls. Nestlings were observed using begging calls along with colourful mouth and postural displays. Distress calls were produced by nestlings and fledglings when captured by a predator, and adults when handled for colour banding. Greeting calls and flight calls were composed of complex phrases, like song, but were short and low pitched, and used for proximate functions.