, Volume 27, Issue 3, pp 713-745

Vocal Diversity and Taxonomy of Nomascus in Cambodia

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It is usually thought that Nomascus gabriellae is the only Nomascus sp. in Cambodia. We studied vocal diversity among different wild populations of Nomascus in Cambodia to assess their taxonomic relationships and to examine whether their vocal patterns correspond to forms previously described for Nomascus leucogenys siki and Nomascus gabriellae. We tape-recorded crested gibbon songs in southern Mondulkiri Province, in central Rattanakiri Province, and in 2 different districts of the Virachey National Park in northern Rattanakiri. We also tape-recorded typical songs of Nomascus leucogenys siki near the type locality of the taxon in the Bach Ma National Park in central Vietnam. We analyzed 40 song bouts from different gibbon groups, including 151 phrases of 33 females and 235 phrases of 39 males. Discriminant analyses revealed marked separation of the most southern songs (Mondulkiri) from those of all other localities. Vocal differences among the 3 gibbon populations in northeast Cambodia (Rattanakiri) are less pronounced; they do not differ more among each other than each of them differs from the northernmost sample from Bach Ma (Vietnam). Vocal characteristics of the study populations revealed no cline, and populations do not differ significantly in vocal variability. We conclude that Cambodian crested gibbons represent 2 distinct taxa: Those from southern Mondulkiri are Nomascus gabriellae, those from northeast Cambodia (Rattanakiri) closely correspond to the sample from Bach Ma (Vietnam) and, together with the latter, represent a different taxon. We provisionally assign them to Nomascus leucogenys siki because of the close geographic distance between Bach Ma and the type locality of the taxon. We postulate that a taxonal boundary exists between southern Mondulkiri and central Rattanakiri and discuss the possible factors that may have acted as distribution barriers.