Sound stream segregation is an important challenge faced by simultaneously vocalizing animals. In duetting passerine birds, coordinating vocal timing helps minimize overlap. Alternatively, in birds that do not coordinate their vocalizations, sound stream segregation may involve other mechanisms. For example, birds are known to use frequency differences to segregate sound streams, and vocalizing at different frequencies may enable them to remain distinct from each other. Here, I present data

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... ing that conspecific individuals of four species of Asian barbets vocalize at distinctly different peak frequencies from each other. Additionally, they also differ in repetition rate such that each species exhibits two peaks in frequency-repetition rate space. However, conspecific individuals across species do not temporally coordinate with each other during vocal interactions, maintaining independent and highly stereotyped individual rhythms together with different peak frequencies. Frequency differences between individuals may facilitate sound stream segregation when calls overlap in time. I hypothesize that simple, uncoordinated temporal rhythms with different frequencies may have given rise to the more complex coordination seen in duetting birds.