Ruppell, J. (2007). Vocal diversity and taxonomy
of Nomascus in central Vietnam and southern Laos. Master's thesis, Anthropology,
Portland State University, vi+81 pp.
Vocal diversity and taxonomy of
Nomascus in central Vietnam and southern Laos
vocalizations have been found to be particularly suitable for studying phylogenetic
relationships among taxa, because taxon-specific characteristics of songs are not
learned but inherited. Based on calls from captive gibbons, Geissmann et al. (2000)
suggested that a previously unrecognized taxon of the genus Nomascus (crested
gibbons) might exist in Central Vietnam. This is supported by more recent research
on the calls of wild crested gibbons suggesting that Nomascus leucogenys siki
may consist of more than one taxon, a southern and a northern one. This hypothesis
should be tested by comparing calls of all potentially distinct populations of Nomascus
of the present study was to determine if vocal differences exist between localities
of Nomascus leucogenys siki occurrence. The study sought to answer the following
questions: 1) Are there vocal differences between localities of Nomascus leucogenys
siki occurrence? 2) What differences are there between the vocalizations of northern
Nomascus leucogenys siki gibbons and southern Nomascus leucogenys siki
The songs of
seven Nomascus populations in Vietnam and Laos were recorded and examined.
Sonograms were used to measure 78 variables of gibbon song which were then analyzed
using statistical analysis.
Results of both
discriminant analysis and multi-dimensional scaling show that the currently named
taxonomic entity Nomascus leucogenys siki can be split into two distinct geographic
populations, northern and southern, based on vocal data. This implies that considerable
vocal diversity exists between the northern and southern groups. To date, there has
been no published description of the vocalizations of wild Nomascus leucogenys
leucogenys or northern Nomascus leucgeonys siki, and only one study on
calls of southern Nomascus leucgeonys siki. Therefore, this study presents
the first evidence that more than one taxon may be involved in what is currently
known as Nomascus leucogenys siki. The results are of relevance for gibbon
conservation, because discovery of a previously undescribed taxon would require a
re-evaluation of conservation priorities for Indochinese gibbons.
Site by Thomas Geissmann.
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