Vietnam Primate Conservation Status Review 2002 - Hoang Lien ...

3.4 Delacour’s langur
Trachypithecus delacouri (Osgood, 1932)
3.4.1 Taxonomy
3.4 DELACOUR’S LANGUR - Trachypithecus delacouri
Two animals of this species were collected during an expedition by J. Delacour and W. Lowe close to
Hoi Xuan on 15th February, 1930. Osgood (1932) described the animals as a new species Pithecus
delacouri, Delacour’s white-backed langur.
Ellerman & Morrison-Scott (1951) placed this taxon as a subspecies to T. francoisi, and most authors
follow this classification. Brandon-Jones (1984) reviewed the status and classified the Delacor’s langur
again as a distinct species. But this view was not widely accepted.
Studies on morphology, behaviour, vocalization and genetics (Nadler, 1994, 1995a, 1996a, 1996b,
1997b; Nadler & Ha Thang Long, 2000; Roos et al., 2001; Nadler & Ha Thang Long, in prep.) clearly
show the differences to other taxa at species level (see 2.3). Furthermore, parasitological comparisons
support the species’ status (Mey, 1994). Most recent publications and reviews have adopted this
classification (Brandon-Jones, 1995; Eudey, 1997; Rowe, 1996; Nowak, 1999; Groves, 2001).
3.4.2 Description
The black and white body colouration of the Delacour’s langur is unique among the South-East
Asian langurs. Apart from the white pubic patch of the females both sexes have the same pelage
colour. The black colouration of the upper body is interrupted by a sharply demarcated line in the
middle of the back with a white colour pelage between this point and a similar sharply demarcated
line just above the knees. As a result the langur looks as if it is wearing a pair of white shorts, indeed
the Vietnamese commonly refer to the species as “Vooc Mong Trang” (the langur with white trousers).
The light whitish-grey cheek hairs are slightly woolly and longer than in other black Indochinese
langurs. The white hairs reach behind the ears where they are tight and form a white patch.
The hair on the head is erected to a crest, the shape is acute and pointed forward. On the back of the
head the hair-stroke forms a vertical crest. The hair-stroke on the head is different to the southern
laotum-species group (Nadler, 1997b).
The long bushy tail differs from all other species of langurs. The hairs are right-angled from the tail
so that the tail appears carrot-like with a diameter of approximately 10 cm close to the root.
The only difference in colouration between the sexes is the white pubic patch in females. It is formed
by an area of unpigmented skin in front of the callosities with whitish hairs. The pubic patches
appear to be irregularly shaped and frequently interspersed with small, sporadic black patches making
them individually characteristic. In contrast to delacouri and francoisi, the laotum females have only
very small white patches. The pubic patch in delacouri and francoisi, therefore, appears white with
black patches, rather than black with white patches as in laotum. The micro-structure of the hair in
delacouri and laotum is also different (Nadler, in prep.).
In some animals the white colouration across the hips occasionally changes to light brown, although
more frequently the change in colouration is restricted to the groin area. The white hair on the
females’ pubic patch can also change colour. The change in colouration is a result of sweat. Females
with babies are especially susceptible to having their pubic patch change colour during the summer.
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