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

Vietnam Primate Conservation Status Review Part 2: LEAF MONKEYS
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This association with karst also may explain why these species of the francoisi-group are allopatic.
Weitzel (1992b) takes this idea further to hypothesize that the distinctive pelage among the forms of
the francoisi-group, may be the result of isolated evolution in karst patches of Vietnam and China.
The association of francoisi-group langurs with karst is assumed to be due to three reasons (Nadler
& Ha Thang Long 2000):
✱ The vegetation and plant communities in limestone areas are species-specific food resources.
✱ Caves used for sleeping provide good protection from predators.
✱ Such caves offer lower temperatures in summer, higher temperatures in winter, and protection
from rain and wind for species not well adapted to climatic conditions and change.
Results of the studies on the feeding plants of langurs show that while Delacour’s and Cat Ba langurs
prefer some tree species associated with limestone, they actually feed on a much broader spectrum of
tree species (Nadler & Ha Thang Long, 2000). Langurs seem to have little to no difficulty using other
vegetation types and plant communities in the same geographical region.
Langurs are mainly hunted inside the caves where they sleep, so their use of caves seems to pose a
serious disadvantage to their survival. High hunting pressure at cave sites would seem to decrease the
langurs’ use of caves. On Cat Ba Island there is furthermore a lack of natural predators, most probably
also in historical time, which makes it unlikely that caves are used by langurs for safety reasons.
Among the other limestone-associated langurs of the francoisi-group, the three northernmost species
(White-headed langur, Cat Ba langur, and Francois’ langur) are most closely connected with limestone.
They regularly sleep in caves throughout the year. Temperatures in these species’ range can drop
below 10°C in winter (and even get close to freezing point). The Delacour’s langur, which occurs
further south, uses caves less frequently. In the Delacour’s range, the cold period is shorter, and the
average temperature is higher.
The southernmost two sub-species of the francoisi-group (T. laotum laotum and T. l. hatinhenis) occur
in north-central Vietnam and central Lao PDR. According to new investigations (Duckworth et al.,
1999), these species occur in some areas without limestone cliffs, which also likely means without
caves.
Burton et al. (1995) reported a close relationship between behaviour and temperature for T. p.
leucocephalus. At temperatures lower than 10 O C, the monkeys move swiftly, eat hastily, and then
move to dry areas such as the underbrush in bamboo stands. At higher temperatures (11-30°C), they
gather on ledges to sun, feed, and rest. To imitate natural conditions, the EPRC provides (isolated)
sleeping boxes in the enclosures of its Trachypithecus species. EPRC observations confirm the close
relationship between temperature and the use of sleeping boxes. With temperatures below 15°C the
langurs use the boxes overnight and when temperatures are below 8-10 O C, the langurs also stay
inside the box during the day and exit only for feeding. Similar observations have been made at the
Francois’ langur breeding center in Wuzhou, China. This institution provides indoor enclosures for
the langurs, and a heating system is used if the temperature drops down below 8 O C (Mei Qu Nian et
al., 1998).
It seems that the primary reason langurs prefer limestone areas is due to the presence of caves and
cracks that act as shelter against climatic conditions, especially temperature. Limestone-area caves
with special micro-climatic conditions have been the main influence on the northern distribution of
this langur group and also explain the limitation of the langurs’ occurrence.
Langurs occasionally dash inside caves when feeling threatened. Lowe (1947) mentioned: “When in
danger, it takes refuge in large holes in the limestone hills on which it lives.” But this flight behaviour
is probably a secondarily acquired behaviour.