The Conservation Status of Gibbons in Vietnam - Gibbon Research ...

Classification & Distribution of Crested GibbonsGenetically, N. nasutus is most closely related to N. hainanus (Roos et al. 2007; Van Ngoc Thinh etal. 2010b; Van Ngoc Thinh et al. 2010e). In the mitochondrial cytochrome b gene, N. nasutus differsfrom N. hainanus in 6.8%, and from the other crested gibbon species in 6.7-8.2% (Roos et al. 2007).N. nasutus separated from N. hainanus about 3.2 million years ago, and from the other crestedgibbon species about 4.2 million years ago (Van Ngoc Thinh et al. 2010b).9.4.2 Western Black Gibbon Nomascus concolorAdult males and juveniles are completely black with a strongly developed crown crest. A fewsingle white hairs may occur in the corner of the mouth. Adult females are pale yellow, yellow,orange or beige brown with a black cap and a large, often rhomboid area with black hairs on theventral area. The amount of ventral black varies. In some females, the whole ventral fur may beblack, strongly contrasting with the light back, at the other end of the range, the ventral fur maybe merely interspersed with some black hairs. Description after Geissmann (1993, 1994, 1995),Geissmann et al. (2000), Groves (2001), Mootnick (2006) and Mootnick and Fan Pengfei (2011).Fully developed male song vocalizations of N. concolor consist of all three different note typesdescribed for male crested gibbons (Geissmann 1993, 1995; Geissmann et al. 2000): single boomsproduced during inflation of the throat sac, staccato phrases, and multi-modulated phrases(Figure 14). The first note of the multi-modulated phrase starts with high frequency (>1 kHz) andis ascending, followed by notes with rapid down-up modulation (u-shaped in the sonogram). Thefemale great call consists of 9-14 notes. The first one or two notes are of ascending frequencyonly, the others are down-up modulated (u-shaped), with the end frequency being higher thanthe starting frequency (Geissmann 1993, 1995; Geissmann et al. 2000; Van Ngoc Thinh et al.2010d; Van Ngoc Thinh et al. 2011).Figure 14. Sonogram showing call sequence of Nomascus concolorAdapted from Van Ngoc Thinh et al. (2011).Genetically, N. concolor is more closely related to the four light-cheeked crested gibbon speciesthan to the other two all-black species N. nasutus and N. hainanus (Roos 2004; Takacs et al. 2005;Monda et al. 2007; Roos et al. 2007; Van Ngoc Thinh et al. 2010b; Van Ngoc Thinh et al. 2010e). Inthe mitochondrial cytochrome b gene, N. concolor differs from N. nasutus and N. hainanus in 6.8-8.2%, and from the light-cheeked crested gibbon species in 4.5-6.2% (Roos et al. 2007). N. concolorseparated from N. nasutus and N. hainanus about 4.2 million years ago, and from the lightcheekedcrested gibbon species about 2.8 million years ago (Van Ngoc Thinh et al. 2010b).9.4.3 Northern White-cheeked Gibbon Nomascus leucogenysMales and juveniles are black with a white cheek beard connecting under a black chin andextending up to the top of the ears. The beard can rarely be pale yellow in juveniles. The beard104