Current status of Western Hoolock
Gibbon Hoolock
hoolock Harlan
in West Garo Hills, Meghalaya, India
J.P. Sati
Zoological Survey of India, Northern
Regional Centre, P.O. IIP, Kaulagarh Road, Dehra Dun, Uttarakhand 248195, India
Email: jpsatizsi@yahoo.co.in
Date of publication (online): 26 February 2011
Date of publication (print): 26 February 2011
ISSN 0974-7907 (online) | 0974-7893 (print)
Editor: Mewa Singh
Manuscript
details:
Ms #
o2292
Received
22 August 2009
Final
received 26 November 2010
Finally
accepted 31 January 2011
Citation: Sati, J.P.
(2011). Current status of Western Hoolock Gibbon Hoolock hoolock Harlan in West Garo
Hills, Meghalaya, India. Journal of Threatened Taxa 3(2): 1520-1526.
Copyright: © J.P. Sati
2011. Creative Commons Attribution 3.0 Unported License. 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: J.P. Sati has been working
on ecology, behaviour and biology of primates with especial reference to
Hoolock Gibbons since the 1980s in the Garo Hills of Meghalaya. Presently, he is working on mammals and
birds of this area. He has
contributed more than 100 research papers and is a coauthor for three books on
wetland birds.
Acknowledgements: I am grateful
to the Director, Zoological Survey of India, Kolkata for the encouragement
throughout the study period. I am thankful to the Officer-in-Charge, Zoological
Survey of India, Dehra Dun and Shillong for providing necessary
facilities. I am also thankful to
the Forest Officials of Meghalaya Governtment for extending various courtesies
and help in conducting the field work.
Abstract:A rapid status survey of Hoolock Gibbon was carried out in
28 localities of West Garo Hills, Meghalaya in March-April 2007. These 28 were among the 32 localities
surveyed previously during 1985-1987 by Alfred & Sati (1990). Gibbons were found in only 15 of the 28
localities. Only 25 groups of
gibbon totaling 82 individuals were observed, compared to 36 groups with 111
individuals recorded at the same sites 20 years ago. Adults comprised nearly 61% of the total individuals,
followed by infants 16%, juveniles 13% and sub-adults 10%. While the proportion in the adult age
class had decreased from 67% in 1985-87, the proportion of individuals in all
other age classes showed slight increase. The sex ratio of males: females was 1:1 for adults as well as sub-adults,
which was the same as in 1985-87 survey. The modal group size was three (44% of groups) as before. However, the next frequent group size
was four (28% of groups), whereas previously the second most frequent group
size was two (30% of groups). Twenty percent of groups had two individuals and 8% of groups comprised
of five individuals. The Hoolock
Gibbon population in the West Garo Hills showed a decreasing trend of 26.2% (82
individuals out of 111 individuals) in 28 localities, when compared with the
previously documented numbers. The
major reasons of their decline are anthropogenic disturbances such as tree
felling for domestic and commercial uses; intermittent cutting of new forest
patches for fresh jhum cultivation, often resulting into canopy gaps as well as
habitat loss; livestock grazing and poaching.
Keywords:Current population, decreasing trend, group size, Hoolock
Gibbon, status survey, West Garo Hills.
Abbreviations:EN - Endangered; IUCN - International Union for
Conservation of Nature; CITES - Convention on International Trade in Endangered
Species
For figures, images, tables --
click here
Introduction
The Western Hoolock Gibbon Hoolockhoolock Harlan, used to be widely distributed in its range in India,
Bangladesh and Myanmar in the recent past (Groves 1972). On the basis of available habitat of
16,250km² in three states of northeastern India, their population was
estimated as 78,700 individuals in 24,640 groups. Tilson (1979) estimated 24,500 individuals of Hoolock in
7,650 groups in 3,480km2 of available tropical evergreen forest
habitat in Meghalaya. Since then,
the total population of Western Hoolock Gibbon in South Asia has drastically
dwindled to a meager 3,000 estimated individuals (Walker & Molur
2007). Alfred & Sati (1990)
reported a population of 130 individuals in 42 groups from West Garo Hills,
Meghalaya. Recently, Gupta &
Sharma (2005) recorded 67 individuals in 39 groups from some parts of West Garo
Hills, Meghalaya.
In recent decades their population has
thus decreased sharply primarily due to destruction of their forest
habitat. It has been listed as
Endangered (EN) by the IUCN (IUCN Red List of Threatened Species 2003) and
continues to occupy the same threat category at present (Brockelman et al.
2008). It is also on the CITES
Appendix I and it is protected under Schedule I of The Wildlife (Protection)
Act 1972 (Amended up to 2003) of the Government of India.
A status survey of Hoolock Gibbons was
undertaken in those localities of West Garo Hills, Meghalaya, where a survey and census was carried out in
1985-1987 by Alfred & Sati (1990). The purpose of this survey was to observe the population trend of this
species in those localities after a gap of nearly 20 years.
Study
area and methods
The present survey was carried out in
the West Garo Hills District of Meghalaya covering a total area of 812km2. It is the western most district of the
state which links Bangladesh on the south and Assam on the west and north,
while the eastern portion connects with east Garo Hills and west Khasi Hills
Districts of Meghalaya. It lies
between latitude 25-260N & 900E at an elevation of
165-1170 m.
The following 28 localities, namely, 1.
Jenjalagri, 2. Anogri, 3.
Rengsangri, 4. Selbalgri, 5. Gandrak, 6. Misimagri, 7. Bibragri, 8. Rombhagri,
9. Chidekgri, 10. Arbella, 11. Khanthragri, 12. Rombagri, 13. Nakatgri
–E, 14. Agoragri, 15. Megapgri, 16. Manchigri, 17. Chenangpara, 18.
Bugonggri, 19. Rongdat, 20. Rongmachuk, 21. Janangpara, 22. Dadenggri, 23. Tura
peak, 24. Balpakram National Park, 25. Baghmara Reserve Forest, 26. Siju
Wildlife Sanctuary, 27. Mahadeo and 28. Ampatgri were surveyed. The size of the National Park, Wildlife
Sanctuary and the Reserve Forest ranged from 61 to 415 km2 while
other non protected areas (private lands) ranged from 3.2 to 8.8 km2(Table 1). Alfred & Sati
(1990) have provided detailed information about the study area.
The survey was carried out for 14 days
in the months of March-April 2007. Two to three localities were covered in a day. The observer would arrive near one of the localities before
the territorial call of gibbons began in the morning hours. After locating the group, its size and
composition were recorded in the data sheet. The observer would then approach a neighbouring group if its
territorial call was heard. The
frequency of call duration ranged from 4-32 minutes with an average of 15
minutes a day which is enough to approach the calling group for its population
count. Usually the singing is
heard in the morning hours and occasionally in the afternoon. At localities where gibbons have
disappeared, the possible factors causing their disappearance were assessed
through interviews with local villagers and forest officials. Group size and composition were
recorded at the time of territorial call of the gibbons or during their
movement towards a food tree. The
age and sex of the individuals was determined by using the body size, body coat
colour, eyebrows and other external characters (Alfred & Sati 1990). The following four age categories were
used: (i) infant (0-2 years of age), (ii) juvenile (2-4 years), (iii) sub-adult
(4-7 years old) and (iv) adult (>7 years), as established by Alfred &
Sati (1990).
Due to the time constraints, only 28 of
the 32 localities previously surveyed could be covered during this rapid
survey. During the present survey,
about 8-10 hours were spent using the same trails, tracks, village sacreds and
conservation reserves localities.
Results
Twenty-five gibbon groups with a total
of 82 individuals were found in 15 of the 28 localities surveyed (Table 1, Fig.
1). Their observed absence in the
remaining 13 localities (46.4%) (marked with solid triangle in Table 1) was
later confirmed by local residents. A solitary individual, a sub-adult female, was encountered only once
during the survey. Only six
localities had two or more family groups, while the remaining nine localities
had one group of gibbons each.
Adult males and females (Images 1 &
2) accounted for nearly 61% of the total groups counted, while sub-adults
10%, juveniles 13% and infants 16% (Image 3) comprised the
other age classes. The sex ratio
of males: females was 1:1 for adults as well as sub-adults. The infants appeared to be between 3 to
5 months and 1.5 years of age. The
mean group size of the current population was observed to be 3.28 (n = 25;
range 2-5).
Two groups with five individuals, seven
groups with four individuals, 11 groups with three individuals and five groups
with two individuals were sighted. Nearly 44% of the groups had three individuals, followed by 28% with
four individuals, 20% with two individuals and 8% with five individuals (Table
2).
The results of the present survey
indicate that there was an over all decreasing trend in all the age categories
of Hoolock Gibbon between 1985-1987 and 2007 (Fig. 2). When the percentage of these
populations was compared with Alfred & Sati (1990), an interesting trend
was observed. Whereas the
proportion of adults has decreased, the proportion of juveniles and infants has
increased. It indicates that the
breeding rate of these gibbons has not been affected but the rate of survival
and formation of new colonies may have been severely affected.
Discussion
While analyzing the population trend of
the present survey with the previous study, it was found that out of eleven
groups with two individuals at that time (1985-87), now five were seen with
increased group size either with three individuals or more; two were stable;
and three groups have disappeared.
An over all decreasing trend was
observed when the population of present survey was compared with that of
1985-87 (Alfred & Sati 1990). During the present survey, an increase in the population was observed at
protected areas like Balphakram National Park, Tura Peak Reserve Forest and
Arbella Reserve which was further supported by the records maintained by the
State Forest Department Govt. of Meghalaya. The maximum decrease was reported from the localities with
smaller forest patches, ranging from 3.2 to 4.8 km2 (either due to
habitat degradation or loss of habitat) which was ascertained by local people
too (Table 1) (Fig. 2).
The comparison of percent population of
juveniles and infants with earlier study brought out an increasing trend in
their population (Fig. 3). It
shows that the breeding rate of the existing population has been affected
positively, but the groups with two individuals have gone down (Table 1). It seems that the new groups are not
being established, probably due to habitat destruction and consequent lack of
suitable territories. At the
localities (13 numbers), where the gibbons have disappeared, the habitat degradation
was very high (15-45% approximately). In these areas the habitat has either been converted to orchards or it
is severely degraded. The slash
and burn agriculture practice, practiced throughout most of the northeastern
India, is also one of the main reasons for habitat loss that directly impacts
survival of gibbons. Being
arboreal, gibbons are also especially susceptible to predation (by dogs and big
cats) and poaching during their long over ground journeys between forest
patches (distance between two forest fragments is more than a kilometer or
so). This is likely to be an
important factor in the decline in their numbers. The major reasons of their depletion are anthropogenic
disturbances, habitat loss, hunting and poaching, canopy gaps, livelihood
issues, livestock grazing, etc. Molur et al. (2003) point out that gibbons are losing 3-4% of their
habitat every year and their population is declining by 1-2% in a year in their
distributional range. Mukherjee et
al. (2008) reported that in Garo Hills of Meghalaya, gibbons are localized in
small fragmented and discontinuous forests. If these factors continue, the time is not far, when the
gibbons will vanish from these 15 localities also. Though the forest cover reports of Forest Survey of India (1991,
1999 and 2005) (Table 3) indicate that there is an over all increase in the
forest cover (but not the gibbon habitat), during the recent observations it
was found that forest habitat where gibbons live has been destroyed in most
areas of the West Garo Hills. Unplanned developmental activities are also a threat to their survival
in the wild. In one of the localities (at Misimagri) two young gibbons were
reported to have died due to electric shock because of over head electric lines
(Sati 2009).
A comparison of the observations made
during this rapid survey with that of the results of 1985-87 study, it was
found that out of 28 localities which were re-surveyed, the gibbons were
observed only in 15 localities (53.5%). This indicates that the gibbons have disappeared from remaining 13
localities (46.5%). Among all the gibbon’s habitat, the smaller fragments
(ranging from 3.2 to 4.8 km2) were found to be more
degraded/disappeared due to upcoming of new tea-gardens, orchards of citreous,
betel-nut, cashew-nut, and slash-and-burn/jhum cultivations as compared to the
remaining larger sized forests (7.9 to 16.3 and more than 60km2). Molur et al. (2005) also stated that
the isolated forest fragments holding the families of about 2–4
individuals are insufficient for long-term survival of the western Hoolock
Gibbon.
To save this species in nature, their
habitat must be protected from further degradation and loss. For reviving their population and
establishment of new groups in particular, the corridors between the existing
forest patches should be developed by planting tropical semi-deciduous and
tropical deciduous tree species such as Grewia desperma,
Dalbergia pinnata, Dalbergiaassamica, Bauhinia purpurea, Vitex glabata, Artocarpus lakoocha, Ficus
benjamina, F. bengalensis, F. concinna, F. pomifera, F. nervosa, F. globella,
F. geniculata, Dendrobium bicaneratum, Cephalostachyum latifolium,
Dendrocalamus hookerii, etc.
References
Alfred, J.R.B. & J.P. Sati
(1990). Survey and census of the Hoolock Gibbon in West Garo
Hills, Northeast India. Primates31(2): 299-306.
Brockelman, W., S. Molur
& T. Geissmann (2008). Hoolock hoolock.
In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.
<www.iucnredlist.org>. Downloaded on 04 February 2011.
Groves, C.P. (1972).Systematics and phylogeny of gibbons, pp. 1-89. In: Rumbaugh, D.M. (ed.). Gibbon and Siamang - Vol. I.
S. Karger, Basal.
Gupta, A.K. & N. Sharma
(2005). Conservation of Hoolock Gibbon (Bunopithecus hoolock) in Meghalaya, pp.87-150. In: Conservation of Hoolock Gibbon
in northeastern India. Envis bulletin,WII Envis Bulletin, Wildlife and
Protected Areas 8(1), Wildlife Institute of India,
Dehra Dun.
IUCN (2003).IUCN 2003 Red List of Threatened Species. <http:// www.iucnredlist.org/>
Down 20 December 2008.
Molur, S., D.B. Jones, W.
Dittus, A. Eudey, A. Kumar, M. Singh, M.M. Feroz, M. Chalise, P. Oriya & S.
Walker (eds.) (2003). Status of South Asian Primates.2003: Conservation Assessment and Management Plan (C.A.M.P.) Workshop Report432pp.
Molur, S., S. Walker, A.
Islam, P. Miller, C. Srinivasulu, P.O. Nameer, B.A. Daniel and L. Ravikumar
(eds.). (2005). Conservation of Western Hoolock Gibbon
(Hoolockhoolock hoolock) in India and Bangladesh: Population and Habitat Viability
Assessment (P.H.V.A.) Workshop Report, 2005. Zoo Outreach Organisation/CBSG
South Asia, Coimbatore, India, 132pp.
Mukherjee, R.P., S.
Chaudhuri & A. Murmu (2008). A note on Hoolock Gibbon (Bunopithecus
hoolock) in northeast, India. Record Zoological Survey of
India 108(1-4): 121-123.
Sati, J.P. (2009). Death of young
Hoolock Gibbons. Zoos’
Print 24(1): 22.
State of Forest Report (1991).Government of India, Ministry of Environment and Forests, Forest Survey of
India, Dehra Dun, 70pp.
State of Forest Report (1999).Government of India, Ministry of Environment and Forests, Forest Survey of
India, Dehra Dun, i-x +1-113pp.
State of Forest Report (2005).Government of India, Ministry of Environment and Forests, Forest Survey of
India, Dehra Dun, i-xviii+1-171pp.
The Wildlife (Protection) Act,
1972 (Amended up to 2003). Wildlife Trust of India, New
Delhi. Natraj Publishers, Dehra Dun, 218pp.
Tilson, R.L. (1979).Behaviour of Hoolock Gibbon (Hylobates hoolock)
during different seasons in Assam. Journal of the Bombay Natural.History Society. 76(1): 1-16.
Walker, S. & S. Molur (Comps.
& Eds.) (2007). Guide
to South Asian Primates for Teachers and Students of All Ages. Zoo
Outreach Organisation, PSG South Asia and WILD, Coimbatore, India.