Status of Bengal
Slow Loris Nycticebus bengalensis (Primates: Lorisidae) in Gibbon Wildlife
Sanctuary, Assam, India
NabajitDas 1,3, J. Biswas 1, J. Das 2, P.C. Ray 1, 3, A. Sangma1, 3 & P.C. Bhattacharjee1, 3
1Primate Research Centre NE India, House No-4, Bye Lane No. 3, Ananda Nagar, P.O. Pandu, Guwahati, Assam 781012,
India
2 Wildlife Areas Development and Welfare Trust M.G. Road, Guwahati, Assam 781001, India
3 Department of Zoology, Gauhati University, Guwahati,
Assam 781014, India
Email: 1 nabajit_das@sify.com, nabajit_das1@rediffmail.com
Date of publication
(online): 26 November 2009
Date of publication (print): 26
November 2009
ISSN 0974-7907 (online) |
0974-7893 (print)
Editor: K.A.I. Nekaris
Manuscript details:
Ms # o2219
Received 27 May 2009
Final received 30 October 2009
Finally accepted 02 November 2009
Citation: Das, N., J. Biswas, J. Das, P.C. Ray, A. Sangma& P.C. Bhattacharjee (2009). Status of Bengal
Slow Loris Nycticebus bengalensis (Primates: Lorisidae) in Gibbon Wildlife
Sanctuary, Assam, India. Journal of Threatened Taxa1(11): 558-561.
Copyright: © Nabajit Das, J. Biswas, J. Das,
P.C. Ray, A. Sangma & P.C. Bhattacharjee2009. Creative Commons Attribution 3.0 UnportedLicense. JoTT allows unrestricted use of this article
in any medium for non-profit purposes, reproduction and distribution by
providing adequate credit to the authors and the source of publication.
Author Details: Nabajit Das:Currently a PhD scholar studying on the Socio-ecology of Bengal Slow Loris in
the protected areas of Assam, India. As a researcher of Primate Research Centre
NE India, he is engaged in primate surveys and behaviourstudies in northeastern India for the last several years.
Dr.
Jihosuo Biswas:Primate Field biologist and programme coordinator of
Primate Research Centre NE India. He has been involved in primate field surveys
and primate conservation education in northeastern India over 10 years. He has
contributed to numerous research papers on primates.
Dr.
Jayanta Das:A large mammal conservationist of northeastern India and currently involved for
the Hoolock Gibbon conservation and education.
Parimal
Chandra Ray:A researcher of the Primate Research Centre NE India. He is interested in behaviour of primates related to habitat change.
Anjan
Sangma:A researcher of the Primate Research Centre NE India, he is interested in behaviours of nocturnal mammals of northeastern India.
Dr.
Parimal Chandra Bhattacharjee: Professor in the Department of Zoology, Gauhati University, is a pioneering worker on the
biodiversity of Northeastern India.
Author Contribution: ND did
research, field work and wrote this paper; JB helped with research designing,
field work and assisted with writing; JD provided technical expertise for
survey, and literature for this paper; PCR & AS assisted in field work; PCB
supervised the Bengal Slow Loris survey in Assam and GWLS.
Acknowledgments: We thank the
Dept. of Environment & Forest, Govt. of Assam, for providing necessary
permission. We specially thank Mr. R. Das, DFO, JorhatForest Division; Mr. K. K. Saikia, Range Officer and
Mr. Dipak Bordoloi, Beat Officer, Gibbon WLS for allowing us to carry
out survey and study at night in the sanctuary and providing all logistic
support. We would have achieved little without the generous assistance of the
personnel of the Forest Department of GWLS, particularly Deben Borah and Sajan Gonju who acted as field
assistants during our survey. We wish to acknowledge Dr. K.A.I. Nekaris of
Oxford Brookes University, UK for providing the necessary advice, literature
and all supports right from the beginning of Bengal Slow Loris studies in this
region. We also acknowledge the generous help and support of Mr. Narayan Sarma and others. This
work was a part of our study on Bengal Slow Loris in Northeast India, supported
by Margot Marsh Biodiversity Foundation, RuffordSmall Grants Foundation, Primate Conservation Inc. and People’s Trust for
Endangered Species.
Abstract:Gibbon Wildlife Sanctuary (GWLS) in the JorhatDistrict of Assam in northeastern India is rich in primate diversity with seven
species. The plains alluvial semi-evergreen
forest patches with high canopy cover support a variety of fauna. In October-November 2008, we carried out a
survey to estimate the population status of Bengal Slow Loris (Nycticebus bengalensis)
in GWLS, a species for which little data are available in India, and
whose conservation status has only recently been changed from Data Deficient to
Vulnerable. We estimated population
abundance of 0.18 loris individuals/km using recce-survey transects’ method in GWLS.
Keywords: Bengal
Slow Loris, Gibbon Wildlife Sanctuary, Nycticebus bengalensis, population abundance.
For Figure, Image, Tables
& Videos – click here
Introduction
Among the primates
of South and Southeast Asia, the slow lorises (Nycticebus spp.) are amongst the least
studied, owing to their nocturnal lifestyle, cryptic nature and relatively
small body size (Srivastava & Mohnot2001). The Bengal Slow Loris (N. bengalensis) is one of five recognized slow loris species, and was previously considered a subspecies
of N. coucang (Groves 2001; Roos 2003). The five
species, recognized based on genetic and morphological analysis are N. bengalensis, N. coucang, N. javanicus, N. menagensis and N.pygmaeus (Roos 2003;
Chen et al. 2006; Nekaris & Jaffe 2007; Groves
& Maryanto 2008). The Bengal Slow Loris is distributed throughout northeastern India,
Bhutan, Myanmar, Cambodia, Southern China, Laos, northern Thailand and Vietnam
(Nekaris & Bearder2007). Due to the limited information,
the Bengal Slow Loris, endemic to South and Southeast Asia, has been until
recently categorized as Data Deficient in the IUCN Red list (2006) and under
Schedule I of the Wildlife (Protection) Act of India, 1972. Recently it was up-listed from Appendix –II
to Appendix – I of CITES (2007) and it is now considered as Vulnerable (Nekaris et al. 2008; Streicher2008) in South and Southeast Asia; in South Asia, however, this assessment was
made on habitat loss alone since few data are available from the field.
To date limited
effort has been devoted to the survey of Bengal Slow Loris population status
and threats to it in Assam; indeed virtually nothing is known about its behaviour and ecology in the wild. Although Choudhuryin 1992 estimated the population size at 16-17,000 individuals (based on
availability of potential habitat), recent publications report that populations
of Bengal Slow Loris are declining (Srivastava & Mohnot 2001; Radhakrishna2006). Habitat destruction, hunting for
food and road accidents are the major threats for this species (Choudhury 1992; Gupta 2001; Radhakrishna2006).
In the present
paper we document the result of a survey of Bengal Slow Loris (Nycticebus bengalensis)
in Gibbon Wildlife Sanctuary in the northeastern state of Assam, India. This study represents the first stage of a
long-term study of behaviour and ecology of this taxon at this site.
Method
Study
area:
The Gibbon Wildlife Sanctuary
(26040’-26045’N & 94020’-94025’E), is an isolated forest patch surrounded
by tea gardens and human settlements. The Gibbon Wildlife Sanctuary (GWLS) was earlier known as “Hollongapar Reserve Forest (RF)”, which was set aside as a
RF in 1881. The sanctuary had been
carved out of the then “Hollongapar RF” named after
the dominant tree species - Holong (Diperocarpus macrocarpus). The original area of the RF was 206ha, but in
1896 some of the areas of the RF were further de-reserved. Subsequently, more forest areas were added to
this RF and by 1997 the total area of the “HollongparRF” increased to 2098.62ha. The
Government of Assam declared this entire RF area as the Gibbon Wildlife
Sanctuary (Image 1) in 1997.
The Sanctuary is now surrounded by
tea gardens almost on all sides and by villages on some. GWLS was once contiguous with a large forest
tract that extended to Nagaland State. The nearest forest areas of Dissoi Valley
Reserve Forests of Nagaland are now separated by a vast stretch of tea gardens
presenting a barrier for the effective migration of wild animals. In early
days, the forests were covered by sporadic evergreen trees with dense “bojal” bamboos (Pseudodactylum sp). In an attempt to grow
well-stocked even-aged regular forest, artificial regeneration was introduced
in 1924, leading to regular plantations. The plantation together with the natural vegetation became a
well-stocked forest, which encouraged biodiversity in subsequent years. The forest type in the GWLS is Assam plains
alluvial semi-evergreen forests, sparsely interspersed with wet evergreen
forest patches (Champion & Seth 1968). The sanctuary is divided into five
distinct compartments. The vegetation is composed of several canopy layers;
most of the components are evergreen in character.
Survey method:
We adopted the ‘recce’ (reconnaissance) survey method (Walsh & White
1999) in conjunction with line transects method (Burnham et al. 1980). The ‘recce’ method
was used to estimate loris encounter rate (MIKE
2006), and has been used in previous studies of closely related species (Nekaris & Jayewardene 2004; Kumara et al. 2006). Surveys were done at night (1800-0200 hr)
from October 28 to November 03, 2008 on foot. Two transects were walked each night and selected randomly to avoid
bias, one between 1800-2130 hr and another between 2230-0200 hr (White &
Edwards 2000). Transects were walked at
a speed of 1km/h.
Due to the high
density of elephants (Elephas maximus) within the ~2100ha study area, the survey team
comprised of three individuals; two were involved in searching both sides of
the transect, with one involved in sighting of other animals (i.e. elephant)
for security reasons, although for best detection possibilities, a team size of
two was desirable (Nekaris et al. 2008). All types of vegetation were searched by PetzlTM headlamp for detection of Nycticebus,
with the aim to detect an orange/red reflection produced from its eye. We used a red filter over the headlamp to
observe and confirm the animal, as red light produces less
disturbance to loris than white light (Nekaris 2003). On
confirmation of loris, data relevant to the survey
including transect length, animal transect distance, number of individuals,
distance of the animal from the observer, angle of the animal from the transect
line, latitude and longitude, time of detection, activity when first detected,
tree height in which it was sighted, tree where it was detected and vegetation
type were recorded (Nekaris & Jayewardene
2004). Photographs of the sighted animal
were taken when possible.
Results
We walked 22.2km
during seven nights of survey in GWLS. The average length of transect was 3.17km per night. Out of the total
area covered, 15% distance was along areas bordering forests and tea estates. The remaining distances walked were in the
interior of the reserve. A total of four
sightings of lone animals (Image 2; Videos 1-3) were made within the seven
survey nights (Table 1). The average
sighting encounter distance from transect was 6m (range 3–10 m) and average
height at which lorises were sighted was 12.25m
(range 10-15 m). The abundance estimate
of this species in GWLS was calculated to be 0.18-individual/km.
On the first two
occasions lorises were seen feeding. The other two were found during their
movement towards the top of trees probably searching for food. All lorises tried
to hide their face away from the white light source. They temporarily froze until we put off the
white lights; after some time they moved to a better position within the trees
to hide (Video 1).
Discussion
The present
study reveals an abundance rate of Bengal Slow Loris population allowing
comparison with the only other available estimate reported for Assam. S. Radhakrishna and
colleagues in 2004 conducted surveys in some parts of Assam, and found 0.03 loris individuals/km and in Gibbon Wildlife Sanctuary (Radhakrishna et al. 2006). Our survey estimated an abundance rate of 0.18
individuals/km, which is slightly higher than that found by Radhakrishna et al. (2006). The present abundance estimate of Bengal Slow Loris in GWLS falls within
the ranges as reported by authors in other parts of its distribution area
(Table 2). This low encounter rate
provides further support to the IUCN Red List status of Vulnerable.
The presence of
Bengal Slow Loris in GWLS indicated the possibility of conducting long-term
population and behavioural studies. Generally all lorisspecies are sparsely distributed throughout much of their range (Nekaris et al. 2008). Bengal Slow Lorisesmay occur only in a few isolated populations in some parts of Assam. Despite a serious danger of becoming extinct
in many parts of Assam (Radhakrishna et al. 2006),
conservation action for this species is still neglected in the western part of
its distribution range.
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