Role of vocalization in species differentiation of Sulawesi tarsiers

Recent work on the tarsiers of Sulawesi indicates that the degree of species differentiation is greater than has hitherto been thought. This is indicated by the acoustic differences between the vocal duets of mated pairs of Tarsius spectrum, Tarsius dianae and tarsiers from the Togian islands (Tomini Bay, Sulawesi). This paper presents further evidence of taxonomic differentiation, based on the vocal behaviour shown during playback experiments. Six adult T. spectrum, kept in captivity, were stimulated by the playback of duets of their own species, those of I dianae and those of Togian tarsiers. The results show that T. spectrum discriminates between the vocalizations of conspecifics and heterospecifics. The behavioural responses of the test subjects to playback of the various duets suggest that I: spectrum is unlikely to interbreed with either I dianae or with the Togian tarsiers. This not only confirms the taxonomic differentiation between T. spectrum and T. dianae, but also supports the specific status of the Togian tarsiers.