The Activity Patterns of a Group of Cantor Dusky Leaf Monkeys (Trachypithecus
This study describes the activity budget of a group of Cantor dusky leaf monkeys (Trachypithecus obscurus) in Penang Botanical Garden, Malaysia. The main objective is to investigate the daily activity budget of T. obscurus in the field. Scanning sampling was employed as the observation method from June 2006 to December 2006. Behavioral observation of 18 individuals were conducted for 8 hours per day, from 0700 h to 1630 h. On average, T. obscurus spent most of their time on feeding (40.02%), followed by the resting (23.96%), moving (22.51%), autogrooming (6.52%), vocalization (3.89%), allogrooming (1.33%), allomothering (0.97%) and the least in playing (0.80%). Chi-square test showed that there is a significant difference among every behavior category of Cantor dusky leaf monkeys. The habitat and canopy used of Cantor dusky leaf monkeys in Penang Botanical Garden were also described.
April 20, 2010; Accepted: June 15, 2010;
Published: August 21, 2010
Trachypithecus obscurus is a member of subfamily Colobinae (Groves,
2001, 2005) which constitutes of eleven subspecies
(Brandon-Jones et al., 2004): T. o. obscurus,
T. o. corax, T. o. flavicauda, T. o. halonifer, T. o. carbo,
T. o. styx, T. o. phayrei, T. o. shanicus, T. o. smithi,
T. o. seimundi and T. o. sanctorum. Geographical distribution of
T. obscurus ranges from Peninsular Malaysia to India (Brandon-Jones
et al., 2004). T. obscurus is commonly called as dusky leaf
monkey or spectacled leaf monkey due to its dietary habit and white mascara
patch over the eye respectively. In Malaysia, it is locally called as cengkong,
lotong mata puteh or lotong bercelak regarding to its unique physical characters
(Marsh and Wilson, 1981). T. o. obscurus (Reids
dusky leaf monkey) is the major subspecies that exists in Peninsular Malaysia,
covering from the north part of Malaysia up until Thailand (Brandon-Jones
et al., 2004). T. o. styx (Perhentian dusky leaf monkey)
occurs in Perhentian Island and probably the adjacent coast (Brandon-Jones
et al., 2004). T. o. halonifer (Cantors dusky leaf
monkey) is another subspecies that can be traced in Dayang Bunting Island, Langkawi
Island and Penang Island (Brandon-Jones et al.,
Previous primate research in Malaysia mostly involved molecular aspects for
both human primate (Shahrom et al., 2005; Lim
et al., 2010) and non-human primates (Jalil
et al., 2008; Md-Zain et al., 2008a;
2010). In addition, molecular systematic studies on
Malaysian primates were also focused at the genus Trachypithecus of both
T. obscurus and T. cristatus (Ernie et
al., 2005; Md-Zain et al., 2005; 2008a).
Other molecular studies from neighbouring country (Thailand) also incorporated
samples of T. obscurus (Chaveerach et al.,
2007; Tanee et al., 2009). Recently, many
primatologists have concentrated on primate ecology and behavior both in the
field (Ampeng and Md-Zain, 2007) and captivity (Arnold
and Barton, 2001; Md-Zain et al., 2008b)
with little emphasis put on dusky leaf monkeys. The field observation of dusky
leaf monkey is relatively scarce due to their shyness, less predictable habits,
greater stealth and tendency to disperse (Chivers, 1980).
In this study, the field observation of Cantors dusky leaf monkeys was
carried out quantitatively to identify their daily activity patterns. It is
hoped that this study can add more information as the other previous behavioral
studies had done especially in understanding the behavior of the Malaysian primates
(Alonso-Spilsbury et al., 2006; Siddique,
2008; Zainudin et al., 2009; Zakaria
et al., 2009).
MATERIALS AND METHODS
This research was conducted in 2006 at Penang Botanical Garden, Malaysia (Fig. 1). The study site is a historical public botanical garden established in 1884 by Charles Curtis, who enthused to bear the seeds of exotic plants from distant lands. Penang Botanical Garden occuppied an area of 30 hectares is inhabiting by fine collection of exotic flora and fauna, especially the long-tailed macaques (Macaca fascicularis) and Cantors dusky leaf langurs. The habituated long-tailed macaque of the garden has earned it another name as the Monkey Garden.
Dusky leaf monkeys are found to exist and forage at seven different sites where
five of the sites are located within the garden while another two are at the
adjacent areas (Fig. 1). The study group of dusky leaf monkeys
at Penang Botanical Garden is composed by 18 individuals that comprises of an
adult male, five adult females, 11 sub-adult females and one infant (Table
|| Map of Penang Botanical Garden indicating the appearance
sites of dusky leaf monkeys
|| Categories and description of study subjects
This subject group is considered as habituated in the term of not running
away or accustomed to the presence of the observer (Curtin,
Preliminary observation was conducted in order to be familiar with subjects
and to determine types of activity patterns of the subjects (Altmann,
1974; Martin and Bateson, 1993). Preliminary observation
was conducted for four days from June 16-21 2006. Scanning sampling was employed
in the intensive observation for 18 days from June 2006 to December 2006. The
sample session was scheduled from 0700 to 1630 h, 8 h per day excluding an hour
and 30 min break. Every sampling subsession was 15 min with 10 min confined
to scan sampling while another 5 min was used to describe and make brief conclusion
of each subsession. Chi-square test was applied to analyze the conducted behavior
data set. This nonparametric test is suitable to analysis the significance of
activity budget which does not follow the normal distribution (Martin
and Bateson, 1993).
RESULTS AND DISCUSSION
Profiles on activity pattern: Cantors Dusky leaf monkey is known
as a social primate. They had been conducting their daily activity within a
social group. Nevertheless, they seldom get involve in social interaction with
other members during observation, where they foraged and fed individually within
the group. The greatest proportion of activity budget of Cantors dusky leaf
monkey was devoted to feeding (40.02%), followed by resting (23.96%) and moving
(22.51%). The indirect social behaviors, autogrooming (6.52%) and vocalization
(3.89%) contributed to a relatively large portion of time compared to the other
social behaviors, allogrooming (1.33%), allomothering (0.97%) and playing (0.80%)
(Fig. 2). Every daily activity of the dusky leaf monkey has
significant different (χ2 = 39380.37; df = 7, p = 0.05) meaning
that there were differences occurred during the daily activity (Table
2). The same behavior patterns shown by Geoffroys marmoset indicated
that more time in feeding and foraging than to social behavior (Passamani,
1998). Present results however contradict with these previous studies which
found out that many colobines spend most of their time in resting rather than
feeding: T. leucocephalus (Li and Rogers, 2004),
T. francoisi (Zhou et al., 2007), Colobus
guereza (Fashing, 2001) and C. vellerosus
(Teichroeb et al., 2003). However, our results
are in line (Zhou et al., 2007) as they found
out that François langurs spent little time on social activities
(grooming and playing). Leaf monkeys will adjust their activity budgets in response
to the change of ecological conditions particularly when food resources are
scarce (Zhou et al., 2007). Thus, in this study,
we found that Cantors dusky leaf monkeys increased their feeding time
may due to maintain a certain daily energy intake.
The daily activity pattern of this study has been recalculated as an average
daily percentage allocated to each activity. As the observation was conducted
during two different periods (June 2006 and December 2006), the daily behavior
allocation was presumed to be affected by some ecological settings or life span.
Feeding behavior was the major behavior of the daily activity budget, by occupying
more than 30% of the daily observation time.
|| Percentage of daily activity budget of dusky leaf monkeys
|| Percentage and Chi-square value of dusky leaf monkeys
activity budget at penang botanical garden
|χ2: 39380.37; p<0.05; degrees of freedom
As no nutrition test has been conducted on the food items consumed by the
langurs, there is no significant evidence showing that either the highest feeding
activity was contributed by the poor nutrient (Li and Rogers,
2004) or the abundance of the food (Passamani, 1998).
The feeding allocation was relatively higher from 12 to 16 December as young
shoot of rain tree (food source) was sprouting within that period. The feeding
time of Rhinopithecus bieti has changed parallel with the seasonality
(Ding and Zhao, 2004). Yet, there was no obvious seasonality
change at Penang Botanical Garden. Dusky leaf monkeys were seen to consume food
more on leaves as many Asian colobines (Dela, 2007;
Solanki et al., 2008; Zhou
et al., 2009).
The abundant and spatial patterning of food resources affect the ranging and
activity budgets of Old World Monkeys (Kinnaird and OBrien,
2000; Fashing et al., 2007). In this study,
the percentage of resting behavior was recorded to be lower when the other motion-based
behavior increased. The most obvious negative correlation was between feeding
and resting behavior (Kurup and Kumar, 1993) and between
playing and resting (Li and Rogers, 2004). However,
it has still employed the second largest portion of the activity budget because
food resources of dusky leaf monkeys in Penang Botanical Garden are abundance.
Results showed that frequency of movement was distributed evenly during the
whole observation period with 20% per day. In daily percentage allocation, movement
has no correlation with feeding behavior. It could be explained that the langurs
movements were not restricted in foraging or resource directed but has been
contributed by other non-foraged movements, such as traveling (Kramer,
2001). Fashing et al. (2007) found out that
C. angolensis spent markedly less time resting, spent more time feeding
and moving and travelled much longer distances that is due to substantial energetic
costs to living in large groups.
In this study, Cantors dusky leaf monkeys allocated less time on social
activities (grooming, playing and allomothering). Allogrooming indicated the
negative correlation with the feeding behavior from 12 to 16 December 2006.
The langurs have reduced their social interaction when they were active in feeding.
Autogrooming and vocalization have shown no trend in daily activity allocation.
Autogrooming is presumed to be a non-functional behavior in this study as it
did not show hygiene (Hutchins and Barash, 1976) or
mutualistic social interaction (Goosen, 1974) during
the observation. Somehow, it was recorded to be in higher frequency during rainy
day. Vocalization has a relatively higher frequency during playing session.
Playing behavior was also distributed evenly with an extremely low percentage.
However, it has recorded relatively larger fraction (>2%) for 2 days of observation.
Apparently, allomothering was affected by the age and development of the infant.
Its percentage only increased during observation in December 2006, when the
infant has grown up and is capable to wander around with its mother. It was
a contrast from the previous study which indicated that the allomothering will
decrease or cease with the growth of the infant (Eimerl and
DeVore, 1980). Overall, every behavior category showed its unique daily
trend during the whole observation. The fluctuation of the dusky leaf monkey
daily behavior was not obvious.
Habitat use: The habitat used was evaluated by the amount of times visited
by the Cantors dusky leaf monkeys. The same method was used by Kaplin
(2001) to determine the habitat use of guenons. Habitat quality may be a
factor causing different activity budget between populations of same species
(Li and Rogers, 2004). Behavior could be affected by
the different habitat use, such as dispersal of resources and habitat-related
adaptations (Singh and Vinathe, 1990). A more widely
ranging or diverse pattern would allow the group to monitor the environment
for resource availability (Garber, 1993).
Site A is the entrance of the Penang Botanical Garden which planted with a
rain tree (Fig. 1). Throughout the observation, site A was
visited most frequently by langurs (Table 3). The prominent
big tree is the favorite food source of dusky leaf monkeys. This situation relates
to previous finding in Blue monkey group that was recorded to visit habitats
with abundant favourite food (Kaplin, 2001).
|| Frequency of appearance of dusky leaf monkey at different
sites within penang botanical garden
Their ranging behavior and distance are the response to the availability of
specific resources and dietary diversity (Kaplin, 2001).
Young shoot or leaves with high nutrient have attracted langurs to visit early
in the morning (Ding and Zhao, 2004). Cercopithecus
aethiops were found to practice optimal foraging theory by spending longer
duration of feeding bouts in higher-quality patches (Whitten,
1998). However, Cantors dusky leaf monkeys did not totally practiced
the optimal foraging theory because their foraging area has occupied a large
patch of garden. They need to employ more energy to forage in such a large area.
This is true as the temporal and spatial distribution of food resources may
be the most important determinant of leaf monkey ranging behaviour (Tan
et al., 2007).
Cantors dusky leaf monkeys seem to exhibit the same ranging habit. Site
B and F are occupied with medium-sized trees with adjacent buildings. A souvenir
shop and rural housing area are located at the central of site B and F, respectively.
However, langur only visited once at the housing area during the observation
(Table 3). Overall, the langur group did not utilize many
sites in Penang Botanical Garden evenly, but had been visiting certain site
regularly with certain essential factor. Presbytis potenziani has occasionally
utilized the gardens and secondary forest besides the predominant primary forest.
It is a common trend in Mentawai primates that exists among the forest communities,
human settlements and commercial logging areas (Fuentes,
Canopy use: Southeast Asian Presbytis and Trachypithecus
tend to use the middle and upper strata of the primary or tall forests
(with canopy > 20 m) (Curtin, 1980; Bennett
and Davies, 1994). The same observation was found at Penang Botanical Garden
while most of the activities of dusky leaf monkeys were concentrated at higher
strata of canopy (site A, C, E and G). These sites are filled with the highest
layer of canopy by tall and broad canopy. The feeding pattern is an indicator
of the abundance and the distribution of the food (Passamani,
1998). Indeed, most of the langurs food sources comes from this layer,
such as rain tree (site A), nutmeg (site C), bamboo (site E) and hill forest
(site G). Normally, dusky leaf monkeys were fed on the tree-crowns of tall trees,
such as figs which have many seeds especially during the fruit scarcity period
Cantors dusky leaf monkeys were observed to utilize every layers of canopy
in range as long as there are supporting substrates ready for them. This finding
supports previous finding by Ampeng (2006) on Presbytis
melalophos chrysomelas which utilized every part of canopy layer in Samunsam
Wildlife Sanctuary, Sarawak. The incomplete habituation of P. potenziani
has restricted them from using the primary supports at <15-10 m at dipterocarps
forest (Fuentes, 1996). Apparently, Cantors
dusky leaf monkeys group at Penang Botanical Garden has no limitation in utilizing
any layer of canopy. They even found out to the range at the housing area (site
F) and cross the electricity cable to site G. From this point, the subjects
are assumed to be habituated to the activitys sites.
We are deeply indebted to several institutions that provided necessary facilities and assistance including Universiti Kebangsaan Malaysia, Department of Wildlife and National Parks and Penang Botanical Garden management. We wish to thank Farhana Shukor and anonymous reviewers for their comments on the manuscript. This research was made possible under grants IRPA 0802020019 EA301, ST-019-2002 and UKM-KRIB-16/2008.
Alonso-Spilsbury, M., I. Escobar-Ibarra, L. Mayagoitia, R. Ramirez-Necoechea and D.Mota-Rojas, 2006. Social and sexual behavior of two newly formed pairs of mexican gray wolf in captivity. Int. J. Zool. Res., 2: 334-343.
CrossRef | Direct Link |
Altmann, J., 1974. Observational study of behavior: Sampling methods. Behaviour, 49: 227-267.
Ampeng, A. and B.M. Md-Zain, 2007. A short note on the methodology of detecting leaf monkeys (Presbytis melalophos chrysomelas and Trachypithecus cristatus) in Samunsam Wildlife Sactuary, Sarawak. J. Wildlife Parks, 24: 7-9.
Ampeng, A., 2006. A study on ecology and behaviour of Presbytis melalophos chrysomelas in the Samunsam Wildlife Sanctuary, Sematan, Sarawak. M.Sc. Thesis, Universiti Kebangsaan Malaysia, Bangi, Malaysia.
Arnold, K. and R.A. Barton, 2001. Postconflict behavior of spectacled leaf monkeys Int. J. Primatol., 22: 243-266.
Bennett, E.L. and A.G. Davies, 1994. The Ecology of Asian Colobines. In: Colobine Monkeys: Their Ecology, Behaviour and Evolution, Davies, A.G. and J.F. Oates (Eds.). Cambridge University Press, ISBN: 0521331536, New York, pp: 129-171.
Brandon-Jones, D., A.A. Eudey, T. Geissmann, C.P. Groves and D.J. Melnick et al., 2004. Asian primate classification. Int. J. Primatol., 25: 97-164.
Direct Link |
Chaveerach, A., T. Tanee, N. Sattayasai, A. Tanomtong, S.A. Suarez and S. Nuchadomrong, 2007. Genetic relationships of langur species using AFLP markers. Pak. J. Biol. Sci., 10: 1445-1451.
CrossRef | PubMed | Direct Link |
Chivers, D.J., 1980. Introduction. In: Malayan Forest Primates: Ten Years Study in Tropical Rain Forest, Chivers, D.J. (Ed.). Plenum Press, New York, pp: 1-28.
Curtin, S.H., 1980. Dusky and Banded Leaf Monkeys. In: Malayan Forest Primates: Ten Years` Study in Tropical Rain Forest, Chivers, D.J. (Ed.). Plenum Press, New York, pp: 107-146.
Dela, J.D.S., 2007. Seasonal food use strategies of Semnopithecus vetulus nestor, at Panadura and Piliyandala, Sri Lanka. Int. J. Primatol., 28: 607-626.
Ding, W. and Q.K. Zhao, 2004. Rhinopithecus bieti at Tacheng, Yunnan: Diet and daytime activities. Int. J. Primatol., 25: 583-598.
Eimerl, S. and I. DeVore, 1980. The Primates. Time-Life Books, Hong Kong.
Ernie, M.M.A., N. Ahmad, K.C. Ang, A. Ampeng and Z.Z. Zainal et al., 2005. Polymerase Chain Reaction (PCR) optimization for COIIrRNA gene fragment of Malaysian Leaf Monkeys. J. Wildlife Parks, 22: 71-76.
Fashing, P.J., 2001. Activity and ranging patterns of guerezas in the Kakamega forest: Intergroup variation and implications for intragroup feeding competition. Int. J. Primatol., 22: 549-577.
Fashing, P.J., E.S. Dierenfeld and C.B. Mowry, 2007. Influence of plant and soil chemistry on food selection, ranging patterns and biomass of Colobus guereza in Kakamega forest, Kenya. Int. J. Primatol., 28: 673-703.
Fuentes, A., 1996. Feeding and ranging in the Mentawai Island Langur (Presbytis potenziani). Int. J. Primatol., 17: 525-548.
Garber, P.A., 1993. Seasonal patterns of diet and ranging in two species of tamarin monkeys: Stability versus variability. Int. J. Primatol., 14: 145-166.
Goosen, C., 1974. Some casual factors in autogrooming behavior of adult stump-tailed macaques (Macaca arctoides). Behavior, 49: 1-11.
Groves, C., 2001. Primate Taxonomy. Smithsonian Institution Press, Washington, ISBN-10: 156098872X..
Groves, C.P., 2005. Order Primates. In: Mammal Species of the World, Wilson, D.E. and D.M. Reeder (Eds.). 3rd Edn., The Johns Hopkins University Press, ISBN: 0801882214., Baltimore, Maryland, USA., pp: 111-184.
Hutchins, M. and D.P. Barash, 1976. Grooming in primates: Implications for its utilitarian function. Primates, 17: 145-150.
Jalil, M.F., J. Cable, J. Sinyor, I. Lackman-Ancrenaz, M. Ancrenaz, M.W. Bruford and B. Goossens, 2008. Riverine effects on mitochondrial structure of Bornean orang-utans (Pongo pygmaeus) at two spatial scales. Mol. Ecol., 17: 2898-2909.
Kaplin, B.A., 2001. Ranging behavior of two species of Guenons (Cercopithecus lhoesti and C. mitis doggetti) in the nyungwe forest reserve, Rwanda. Int. J. Primatol., 22: 521-548.
Kinnaird, M.F. and T.G. O'Brien, 2000. Comparative Movement Patterns of Two Semiterrestrial Cercopithecine Primates: The Tana River Crested Mangabey and the Sulawesi Crested Black Macaque. In: On the Move: How and Why Animals Travel in Groups, Boinski, S. and P.A. Garber (Eds.). University of Chicago Press, Chicago, pp: 327-350.
Kramer, D.L., 2001. Foraging Behavior. In: Evolutionary Ecology: Concepts and Case Studies, Fox, C.W., D.A. Roff and D.J. Fairbairn (Eds.). Oxford University Press, New York, pp: 232-246.
Kurup, G.U. and A. Kumar, 1993. Time budget and activity patterns of the Lion-Tailed Macaque (Macaca silenus). Int. J. Primatol., 14: 27-39.
Li, Z. and E. Rogers, 2004. Habitat quality and activity budgets of white-headed langurs in fusui, China. Int. J. Primatol., 25: 41-54.
Lim, L.S., K.C. Ang, M.C. Mahani, A.W. Shahrom and B.M. Md-Zain, 2010. Mitochondrial DNA polymorphism and phylogenetic relationships of proto malays in peninsular Malaysia. J. Biol. Sci., 10: 71-83.
CrossRef | Direct Link |
Marsh, C.W. and W.L. Wilson, 1981. A Survey of Primates in Peninsular Malaysian Forests. Universiti Kebangsaan Malaysia and University of Cambridge, Malaysia, United Kingdom.
Martin, P. and P. Bateson, 1993. Measuring Behaviour: An Introductory Guide. 2nd Edn., Cambridge University Press, Cambridge, ISBN: 978-0521535632, pp: 238.
Md-Zain, B.M., J.C. Morales, M.N. Hassan, A. Jasmi and D.J. Melnick, 2005. Phylogenetic position of the genus Trachypithecus as inferred from Y-chromosome and autosomal DNA sequences. Malaysian J. Biochem. Mol. Biol., 12: 48-54.
Md-Zain, B.M., J.C. Morales, M.N. Hassan, A. Jasmi, M. Lakim, J. Supriatna and D.J. Melnick, 2008. Is Presbytis a distinct monophyletic genus: Inferences from mitochondrial DNA sequences. Asian Primates J., 1: 26-36.
Direct Link |
Md-Zain, B.M., M.Y. Yen and I.A. Ghani, 2008. Daily activity budgets and enrichment activity effect on Chimpanzees (Pan troglodytes) in captivity. Sains Malaysiana, 37: 15-19.
Direct Link |
Md-Zain, B.M., S.J. Lee, M. Lakim, A. Ampeng and M.C. Mahani, 2010. Phylogenetic position of Tarsius bancanus based on partial cytochrome b DNA sequences. J. Biol. Sci., 10: 348-354.
CrossRef | Direct Link |
Passamani, M., 1998. Activity budget of geoffroy's marmoset (Callithrix geoffroyi) in an Atlantic forest in Southeastern Brazil. Am. J. Primatol., 46: 333-340.
Direct Link |
Shahrom, A.W., L.S. Lim, B.M. Md-Zain, M.C. Mahani and S. Noor-Azma, 2005. 2-D Facial reconstruction (When skull is not available) using mitochondrial DNA (MTDNA) phylogeny tree and image morphing techniques: A preliminary study. Int. J. Med. Toxicol. Legal Med., 8: 1-5.
Siddique, Y.S., 2008. Breeding behavior of Copsychus saularis in Indian-sub-continent: A personal experience. Int. J. Zool. Res., 4: 135-137.
CrossRef | Direct Link |
Singh, M. and S. Vinathe, 1990. Inter-population differences in the time budgets of Bonnet Monkeys (Macaca radiata). Primates, 31: 589-596.
CrossRef | Direct Link |
Solanki, G.S., A. Kumar and B.K. Sharma, 2008. Feeding ecology of Trachypithecus pileatus in India. Int. J. Primatol., 29: 173-182.
Stevenson, P.R., 2004. Fruit choice by woolly monkeys in tinigua national park, Colombia. Int. J. Primatol., 25: 367-381.
Tan, C.L., S. Guo and B. Li, 2007. Population structure and ranging patterns of Rhinopithecus roxellana in zhouzhi national nature reserve, Shaanxi, China. Int. J. Primatol., 28: 577-591.
Tanee, T., A. Chaveerach, R. Sudmoon, A. Tanomtong and P. Mokkamul, 2009. Genetic relationships of cercopithecidae in thailand as inferred from rDNA ITS regions. J. Biol. Sci., 9: 51-56.
CrossRef | Direct Link |
Teichroeb, J.A., T.L. Saj, J.D. Paterson and P. Sicotte, 2003. Effect of group size on activity budgets of Colobus vellerosus in Ghana. Int. J. Primatol., 24: 743-758.
Whitten, P.L., 1998. Effects of patch quality and feeding subgroup size on feeding success in vervet monkeys (Cercopithecus aethiops). Behaviour, 105: 35-52.
Direct Link |
Zainudin, R., A.R. Mustafa, B.M. Md-Zain, M.N. Shukor, A. Norhayati and R.F. Inger, 2009. Characteristics of bornean frog (genus: hylarana) calls from the sarawak population, Malaysia). Sains Malaysiana, 38: 619-624.
Zakaria, M., M.N. Rajpar and A.S. Sajap, 2009. Species diversity and feeding guilds of birds in paya indah wetland reserve, Peninsular Malaysia. Int. J. Zool. Res., 5: 86-100.
CrossRef | Direct Link |
Zhou, Q., C. Huang, Y. Li and X. Cai, 2007. Ranging behavior of the francois langur (Trachypithecus francoisi) in the Fusui nature reserve, China. Primates, 48: 320-323.
Zhou, Q., Z. Huang, X. Wei, F. Wei and C. Huang, 2009. Factors influencing interannual and intersite variability in the diet of Trachypithecus francoisi. Int. J. Primatol., 30: 583-599.