Habitat suitability, threats
and conservation strategies of Hump-nosed Pit Viper Hypnale hypnale Merrem (Reptilia: Viperidae)
found in Western Ghats, Goa, India
Nitin S. Sawant 1,
Trupti D. Jadhav 2 & S.K. Shyama 3
1 Research Scholar, 3 Reader, Department of Zoology, Goa University, Goa 403206,
India
2 H.No. 359-A, St.Inez, Altinho,
Panaji, Goa 403001, India
Email: 1 nitinnature@yahoo.co.in
Date of publication (online): 26 October 2010
Date of
publication (print): 26 October 2010
ISSN
0974-7907 (online) | 0974-7893 (print)
Editor: Gernot Vogel
Manuscript details:
Ms # o2490
Received 22 June 2010
Final received 29 September
2010
Finally accepted 03 October
2010
Citation: Sawant, N.S., T.D. Jadhav & S.K. Shyama (2010). Habitat
suitability, threats and conservation strategies of Hump-nosed Pit Viper Hypnale hypnale Merrem (Reptilia:
Viperidae) found in Western Ghats, Goa, India. Journal of Threatened Taxa 2(11):
1261-1267.
Copyright: © Nitin S. Sawant, Trupti D. Jadhav & S.K. Shyama 2010. 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: Nitin
S. Sawant employed with
WWF-India, as State Director of the Goa State office, with responsibilities of
designing, planning and executing environmental awareness and conservation
programme in the state and to address issues pertaining to environment and
wildlife. Actively involved in rescue operations of snakes and other wild
animals in association with the forest department of Goa.
Trupti D. Jadhav founder member of Nirmiti, a
local NGO working towards documentation of biodiversity and its conservation. Pursued MSc. in zoology through Goa University.
Presently involved in wildlife conservation activities.
Dr. S.K. Shyama,Associate Professor, Department of Zoology, Goa University.
Author
Contribution: NSS and TDJ
have contributed in the field work and writing of the
manuscript. SKS contributed in the
final editing of the manuscript.
Abstract:Recent studies indicate that
most species are best conserved in their natural community, which results in
niche conservation. Depletion of any species is an irreversible change. In the
present study the habitat ecology, threats and conservation strategies for the
Hump-nosed Pit Viper Hypnale
hypnale are suggested.
The present study was undertaken in some protected areas (PAs) of Goa and the
cashew plantations adjoining these PAs. H.hypnaleprefers cool and moist places; most of the females of this species are found to
spend the period from post monsoon to late summer in the cashew plantations
adjoining and within the PAs, making them more susceptible to anthropogenic
threats. We conclude that this pattern of seasonal changes in habitat use is mostly
a consequence of niche conservation. However, this preference for a particular micro-habitat emphasizes the importance for the conservation
of this snake population and although the most suitable habitat in the Western
Ghats, for this species is included in the protected areas, specific guidelines
are needed to assess conservation needs.
Keywords:Conservation, Goa, habitat, Hypnale hypnale, threats,
Western Ghats.
For figure, images & table -- click here
Introduction
The habitat of a species can be defined as that
portion of a multi-dimensional hyperspace (defined by any number of habitat
factors) that is occupied by a given species (Whitaker et al. 1973). Data pertaining to interspecific niche
partitioning by snakes has lagged behind that of other vertebrate groups,
notably lizards and birds (Schoener 1977; Toft 1985). Descriptions of the preferred habitat is currently available
for very few snake species (Reinert 1993) therefore, snakes are not well
represented in studies of habitat selection. This is partly due to their secretive nature. They are difficult to locate and
sightings are probably biased in favor of habitats where they are most
visible. Measures of habitat
suitability need to evaluate micro-habitat usage and
animal movement patterns (Gurnell et al. 2002). Studies on some snake species suggest that individual snakes
do actively select a preferred portion of their environment (Reinert 1984;
Weatherhead & Charland 1985; Burger & Zappalorti 1988; Weatherhead
& Prior 1992) and the habitat selection is influenced by complex biotic and
abiotic factors (Reinert 1993). Although some species are highly specialized and can exploit a narrow
range of habitat, most taxa utilize a broader range, at least occasionally
(Heatwole 1977). Thus, it is also
important to understand why species shift among habitat type.
The State of Goa is located along the central
west coast of India, lying between latitude 14051’-15048’N
& 73041’-74020’E, with an area of 3702km2. The forests of Goa have been classified
into various types which include the west coast tropical evergreen, cane
brakes, wet bamboo brakes, west coast semi-evergreen, moist bamboo brakes,
lateritic semi-evergreen forest, slightly moist teak forest, southern moist deciduous
forest, southern secondary moist mixed deciduous forest, south Indian
sub-tropical hill savannah woodland, southern sub tropical hill forest,
lateritic scrub and dry tropical river rain forest (Champion & Seth 1968).
The Hump-nosed Pit Viper belongs to Family
Viperidae and Subfamily Crotalinae. Three species of pit vipers are found in Goa viz. Trimeresurus malabaricus, Trimeresurus
gramineus and Hypnale hypnale (Khaire 2006; Pradhan 2008; Sawant et al.
2010). Out of these three species T. malabaricus is endemic to the Western Ghats, T. gramineus is reported from Eastern and Western Ghats and Hypnale hypnale is found in the Western Ghats and Sri Lanka
(Smith 1943; Whitaker 1978). Whereas H.
hypnale has been recordedmainly from the southern part (up to about 160N)
of the Western Ghats and Sri Lanka (Smith 1943; Murthy 1990; Maduwage et al
2009), Maduwage et al. (2009) found no differences in specimens from the
Western Ghats and from Sri Lanka.
The H.
hypnale is both
terrestrial and semi-arboreal in habit (Murthy 1990). The protected areas in Goa cover most of the Western Ghats
region. The Goa region occupies
about 2% of the total area of the Western Ghats (Joshi & Janarthanam
2004). The forests of the Western
Ghats are very rich in wildlife and endemic species (Gadgil & Guha
1992). Many reptiles in the
Western Ghats have restricted distribution, which is a major reason for many of
them (63 Species) being threatened (Kumar et al. 1998). Despite high endemism and threat, there
are only a few studies on the habitat preferences and community structure of
reptiles in the Western Ghats (Inger et al. 1987; Bhupathy & Kannan
1997). The Western Ghats of south
India have experienced large scale changes over the
last century because of expansion and urbanisation (Nair 1991). Many of the world’s species are
threatened due to habitat destruction and fragmentation, which is the major
cause of species endangerment (Dodd 1987; Mittermeier et al.1992; Wilson 1992;
Losos et al. 1995; Fahrig 1997). Understanding
the components of a snake’s spatial and habitat ecology, such as movement
patterns and habitat selection are therefore important in identifying features
necessary for the preservation of a species (Dodd 1987, 1993; Reinert 1993).
The habitat of H. hypnale in Goa (Western Ghats region) is vulnerable to
several threats including climate change and anthropogenic threats, thus it is
important to identify its macro and micro-habitat. Only limited information is available
on the ecology of this snake and the studies of its spatial ecology have never
been conducted. Thus, this study
was undertaken to study the habitat of this species, seasonal variation in
habitat use, to identify the threats and device strategies for the conservation
of its habitat and population.
Materials and
Methods
The sites selected for the present study were
the PAs in Goa which form a part of northern Western
Ghats and run in a north-south direction (Fig. 1). The sites selected were Mhadei Wildlife Sanctuary (MWS),
Bhagwan Mahaveer Wildlife Sanctuary and National Park (BMWS & NP), Bondla Wildlife Sanctuary
(BWS), Netravali Wildlife Sanctuary (NWS), Cotigao Wildlife Sanctuary (CWS) and
the cashew (Anacardium
occidentale) plantations
within and adjoining these PAs. The study sites lie at an average altitude of 20 to 800 m (from south to
north).
Intensive surveys on foot were carried out in
the Western Ghats region, from June 2005 to January 2009, in the five
sanctuaries mentioned above. The
possible habitat sites of H.
hypnale were marked with
band transects. An average path or
road of 2.5km length was considered with a width of 20m (10m on both side of
the transect). The distribution ofH. hypnale was recorded using the
transect sampling method as described in Dahanukar & Padhey (2005). Geographical
positioning of the each location was obtained by hand-held Geographical
Positioning System (GPS). Humidity and temperature were also recorded using a hygrometer and a
mercury thermometer. In the cashew
plantations the temperature and humidity of the leaf litter core was also
recorded.
The transects were monitored regularly during day and night
hours in different seasons and local inputs (secondary data) were also
recorded. The survey involved an
active search i.e. close visual inspection of shrubs, trees, ground,
leaf litters. Secondary data
included the collection of H.
hypnale from local
people (live & occasionally dead). During the survey the threats to this snake population and its habitat
were also identified. The snakes were collected by snake sticks. All the snakes encountered during the
survey were identified up to species level following the methodology of Smith
(1943), Murthy (1989), and Daniel (2002). The number of snakes and their sex was recorded.
The data recorded from transects was used to
estimate the species distribution in each study area. The data was also used to find the abundance of the species
during different seasons. Variance
among the abundance of the H.
hypnale in study sites
(forest area and cashew plantation) during different seasons (summer, monsoon,
post monsoon and winter) was tested using the one-way ANOVA. Difference of p < 0.05 was regarded
as statistically significant. All
the calculations were carried out using the Microsoft Excel Software 2007.
Results
In the present study, H. hypnale (Image 1) was found to occur in all of the
study sites surveyed except in BWS (Fig. 1). Incidentally, locals have reported sighting of this species
in precincts of BWS. The average temperature in all the study areas ranged from
20.88 ± 5.25 0C to 32.44 ± 0.88 0C. Whereas the humidity ranged from 53 ± 4
% to 93 ± 2 %. GPS records showed
that H.
hypnale was found at an
altitude range of 35 to 627 m. It
was observed that amongst the forest types present in the PAs of Goa, the H. hypnale preferred the west coast tropical evergreen,
cane brakes, moist bamboo brakes, slightly moist teak forest, southern moist
deciduous forests, south Indian sub-tropical savannah woodland, and southern
sub-tropical hill type. During the
present study, it was observed that the H.
hypnale is an ambush
predator and wiggles its tail to attract the prey, on
some occasions it was encountered feeding on sinks, frogs and agamids. The predators of H. hypnale include predators such as the Crested
Serpent-eagle, coucal, peacock and cobra which were
sighted preying on H.
hypnale; other potential
predators include shikra, vipers, mongoose and civet cats. The same was also
reported by locals. The
list of floral and faunal associates of the H.
hypnale is given in
(Table 1). In most of the
sightings the H.
hypnale was found on the
ground beneath the leaf litter. However, occasionally it was found on shrubs and herbs at an average
height of up to 1.3 ft from the ground. It was also noted that during the post monsoons, winters and late
summers the H.
hypnale moved to the
adjoining cashew plantations. The number of individuals sighted in the forest
area and the cashew plantation during different seasons is given in Fig.
2. The Analysis of Variance (i.e.
one-way ANOVA) for testing the abundance of H.
hypnale for forest area
with respect to different seasons showed that p = 0.254, df = 3, F =1.539,
whereas, the one-way ANOVA to test the abundance of H. hypnale for the cashew plantation with respect to
different seasons showed that p = 0.227, df = 3, F = 1.66.
It was noted that the population which moved to
the adjoining cashew plantations had low male: female ratio i.e. 0.227. It was also seen that most of the
females that moved to the cashew plantations were gravid females. Thus, 65.9% of the total females
sighted in the cashew plantations were gravid females. The temperature of the leaf litter core
was 1.96 ±1.32 0C lower than the ambient temperature, whereas the
humidity was 5 ± 1.87 % higher than ambient humidity as compared to the forest
area where the leaf litter temperature was 0.42 ± 0.13 0C lower and
humidity was 1.8 ± 0.83 %, higher than the ambient temperature and humidity
during the post monsoon and winter seasons. During the present study the following threats were
identified.
(i) Habitat fragmentation due to encroachment
and mining activities due to which most of the areas neighbouring the protected
areas are affected.
(ii) The increasing population of peacocks
might have put immense pressure on the population of the H. hypnale as it is one of the dominant predators found
in all the study sites.
(iii) The major threat faced by the H. hypnale population is the anthropogenic pressure,
especially due to their shift in habitat to the cashew plantations during the
post monsoon and winter where they are killed out of fear by the labourers
during the clearance of shrubs in the cashew plantations (Image 2).
DISCUSSION
Habitat destruction is the major cause of
endangerment for many of the world’s threatened species (Losos et al. 1995;
Fahrig 1997). It is therefore
important to identify the habitats utilized by this species of pit viper and to
protect the habitat relevant for their conservation. Identifying the habitat requirement, activity pattern and
spatial distribution of a species is important towards the ecological
management of this specie’s population and habitats.
The present study revealed that the H. hypnale is in the Western Ghats (India) and
distributed in parts of Maharashtra, Goa and southern parts of India. We observed that the H. hypnale preferred most of the forest type present in
the protected areas of Goa. However, during the present study there was no record of the H. hypnale in the BWS. Incidentally, the locals reported the presence of H. hypnale in the vicinity of BWS. It is the smallest wildlife sanctuary of Goa
and amongst the forest type preferred by the H. hypnale, only cane brakes, wet bamboo brakes, southern
secondary moist mixed forest and west coast semi-evergreen, moist bamboo brakes and lateritic semi
evergreen forest patches prevail in BWS. A possible factor
which has affected this species may be the presence of a zoological
garden in the sanctuary which attracts many tourists and a continuous flow of
vehicles which causes disturbances of the habitat. Secondly this species shows a shift in habitat during
different seasons, for which the hygrothermal profile such as cool and moist
climate, leaf litter, suitable retreat and breeding site is not available at
BWS throughout the year.
We observed that the H. hypnale occupied a broader altitudinal range (35 to
637 m) which suggests that factors such as
temperature, humidity, basking sites and prey availability play a major role in
habitat selection. These
observations are in agreement with the report of Dial (1978), Huey et al.
(1989), Madsen & Shine (1996), Kearney (2002), and Pringle et al.
(2003). Hypnale hypnale is mostly terrestrial but has occasionally
been encountered on herbs and shrubs; this excursion is obviously a part of the
process of thermo-regulation. Shine et al. (2005) believed that climbing above ground level to
facilitate thermo-regulation is widespread in snakes as in other ectotherms.
During the present study, it was observed that
the H.
hypnale showed a shift
in habitat from natural confines within the protected areas into the cashew
plantations. There are no previous
records of such a shift in habitat shown by the H. hypnale. Interestingly, such a shift in habitat
coincides with the breeding season and these interim
movements are mostly exhibited by the females, especially by the gravid females. Males were very rarely encountered in
the cashew plantations. The
transient shift by the gravid females into the cashew monoculture merits
discussion. The micro
habitat requirement of the breeding individuals is perhaps best met in
the cashew plantation owing to the density and thickness of the leaf litter. Reinert (1993) suggested that the need
to locate essential resources such as food, shelter and gestation sites,
influences habitat selection by snakes. A few studies (Houston & Shine 1994; Mullin & Cooper 2000; Shine
& Sun 2002) showed that reptiles prefer habitat with a
high prey abundance. Janzen
& Schoener (1968) suggested that factors such as general reduction in the
forest productivity in the dry seasons affect most animals including reptiles
and their prey. Thus, less prey
availability is the possible reason for the shift in habitat from the forest
area to the cashew plantation. This also explains why there is a difference in sightings during
different seasons. Henderson et
al. (1979) reported that the effect of rainfall on snake activity may be indirect by affecting prey availability. The present study revealed that leaf
litter core temperature was 1.96 ±1.32 0C lower than the ambient
temperature, whereas the humidity was 5 ± 1.87 % higher than ambient humidity in the
cashew plantation as compared to the forest area. This cool and humid climate below the leaf litter provides a
good micro-climate for reptiles which is the major
prey base for the reptiles. This
in turn forms the prey base for the H.
hypnale. This is supported by
Kumar et al. (2001). Lima
& Dill (1990) suggest that specific features of the leaf litter help
reptiles to meet the conflicting demands of thermo-regulation, predator
avoidance and participation in other activities.
Hypnale hypnale is a species of Western Ghats (India) and faces
tremendous anthropogenic pressure. Habitat fragmentation due to mining activities around the protected
areas is the immediate threat to this species. H. hypnale is
a terrestrial species and ambush predator, which requires habitat such as a favourable
hygrothermal profile, thick and moist leaf litter etc. The increase in avian predators such as
the peacock has drastically reduced the population of this species and other
reptiles and amphibians in some areas. During the post monsoon and winter periods, ground clearance in the
cashew plantation is carried out to allow free movement under the plantation
for cashew collection. During this
process H.
hypnale are encountered
under small bushes and thick leaf litter. Thus this behavior of shifting habitat, especially by the gravid females
to the cashew plantations is a cause of concern from the conservationist’s
point of view since the work force employed for such massive clearance, kills
the snake out of fear. Such
phenomenon is not uncommon in some parts of Goa, especially in places such as
Sattari and Sanguem, and necessitates a conscious effort of educating the
workers, on the conservation importance of these reptiles. Goa is a small state and mining is a
major source of income for the state, most of the mining leases are around the
protected areas, thus it has become very difficult to protect the habitat of
this species. It is, therefore,
important to create awareness among the communities to protect the habitat in
order to protect these species. The government agencies (policy makers) play a vital role in directly
conserving the habitat of the species, which in turn can aid in the indirect
conservation of this species which is endemic in the
Western Ghats and Sri Lanka.
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