Lowland forest butterflies of the Sankosh River catchment, Bhutan
Arun P. Singh
Ecology and Biodiversity
Conservation Division, Rain Forest Research Institute (ICFRE), P.O. Box no.
136, Deovan, Sotai, Jorhat, Assam 785001, India
Email: ranoteaps@gmail.com,
singhap@icfre.org
Date of
publication (online): 10 October 2012
Date of publication
(print): 10 October 2012
ISSN 0974-7907
(online) | 0974-7893 (print)
Editor: Ullasa Kodandaramaiah
Manuscript
details:
Ms # o2625
Received 12
November 2010
Final received
17 July 2012
Finally accepted
20 August 2012
Citation: Singh, A.P. (2012). Lowland forest butterflies
of the Sankosh River catchment, Bhutan. Journal of Threatened Taxa 4(12): 3085–3102.
Copyright: © Arun P. Singh 2012. 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: Arun P. Singh works on the
conservation of biodiversity of Himalaya with special reference to butterflies
and birds since 18 years. His research works include ecology, taxonomy, and
environmental impact assessment (EIA) studies. Presently, he heads the Ecology
and Biodiversity Conservation Division, Rain Forest Research Institute (ICFRE),Jorhat, Assam.
Acknowledgements: This study was part of the EIA of the proposed Indo-Bhutan Sankosh Hydro Electric Power project at Kerabari,
being carried out by the Indian Council of Forestry Research and Education
(ICFRE), Dehradun. The author is thankful to DG (ICFRE), DDG (Extension, ICFRE)
& ADG and Sudhir Kumar, project manager (EIA
Division, ICFRE), and Director, FRI, India, and Department of Energy and Range
Officer, Kalikhola, Forest Department of the Royal
Government of Bhutan for providing the necessary facilities to carry out this
study.
Abstract: This paper provides information
on butterflies of the lowland forests of Bhutan for the first time. As a part of the biodiversity impact
assessment for the proposed Sankosh hydroelectric
power project, a survey was carried out along the SankoshRiver catchment to study the butterfly diversity. The aim of the study was to identify
species of conservation priority, their seasonality and to know the butterfly
diversity potential of the area. Surveys were carried out during five different seasons (winter, spring,
pre-monsoon, monsoon, post-monsoon) lasting 18 days from January 2009 to March
2010. Pollard walk method was used
to assess the diversity on four-line transects within 10–12 km radius of
the proposed dam site. Two hundred
and thirteen species, including 22 papilionids, were
thus sampled. Eleven species
amongst these are listed in Schedules I and II of the Indian Wildlife (Protection)
Act, 1972, of which 10 taxa (Pareronia avatar avatar, Nacaduba pactolus continentalis, Porostas aluta coelestis, Elymnias vasudeva vasudeva, Mycalesis mestra retus, Melanitis zitenius zitenius, Charaxes marmax, Athyma ranga ranga, Neptis manasa manasa and Neptis soma soma) are of conservation priority as they are ‘rare’ in occurrence
across their distribution range in the region. The maximum number of
species (128) were recorded during the spring season (March) and lowest
(66) during July (monsoon). The
seasonal pattern of variation in diversity was very typical of the pattern
found in other areas of the lower foothills and adjoining plains of the
Himalaya. Relative abundances of
butterflies during spring varied significantly (p<0.05) as compared to
winter, pre-monsoon and post-monsoon seasons. However, species composition changed
with every season as Sorensen’s similarity index varied between
0.3076 to 0.5656. All these
findings suggest that the lowland forests of Bhutan hold a rich and unique
diversity of butterflies during every season of the year thus having a good
potential for ecotourism. Establishment of a butterfly conservatory and park as a ‘biodiversity
offset’ for conservation of ‘rare’ species along with more field surveys in the
study area will be a way forward along with the present work to bridge the exisiting gaps in knowledge on butterflies of the
sub-tropical lowland forests of the Himalayas.
Keywords: Indian
Wildlife Protection Act 1972, Phibsoo Wildlife Sanctuary,
rare species, seasonality, Shorea robusta, Simpsons index, Sorensen’s index, sub-tropical.
For
figures, images, tables -- click here
INTRODUCTION
Reducing
the impact of large dams on biodiversity calls for knowing where species,
ecosystems and ecological functions are located. Lack of that information is one of the
serious impediments and is a result of poor support for biological surveys,
research and academic work on taxonomy and ecology. IUCN, UNEP and WCD recommendations on
dams and biodiversity (McAllister et al. 2001), highlight the need to avoid
biodiversity ‘hotspots’ and ‘hot’ portions of gradients. The avoidance of areas rich in species
and endemic species needs to be given high priority in selection criteria. That includes both, choosing watersheds
and sites within watersheds, and taking into account ‘hotspots’ and gradients
in biodiversity. Besides, the
recommendations also highlight the need to carry out research on biodiversity
as our knowledge on biodiversity is incomplete and geographic distributions are
poorly documented (McAllister et al. 2001). The environmental impact of large dams
on lower groups of organisms, such as insects, is hardly ever studied for loss
of wildlife in India (Mishra 2009).
According
to Conservation International, Bhutan forms a part of the ‘Eastern Himalaya
Biodiversity Hotspot’ which is one of the 34
biodiversity hotspots of the world today (www.biodiversityhotspots.org/). A home for over 50 species of
rhododendrons, large numbers of orchids (http://www.bhutan2008.bt/en/node/276),
Bhutan is also one of the 221 global endemic bird areas with over 770 avian
species (Inskipp et al. 1999). Bhutan along with northeastern India are
the meeting place of the central Asian and Chinese sub-divisions of the Palaeartic region with the peninsular Indian and Malayan
subdivisions of the oriental region and are therefore considered very rich
areas in terms of butterflies. With
incredible variations, from subtropical to alpine along the altitudinal
gradient (100–4,200 m), Bhutan presents a large variety of habitats for
butterflies. The adjoining state ofSikkim which lies west of Bhutan in India has over 689
species (Haribal 1992). Besides, 962 taxa of butterflies have
been identified from northeastern India from Sikkim, Assam, Manipur; Meghalaya, Nagaland Mizoram and northern Myanmar (Evans
1932). On the other hand Wynter-Byth (1957) gives a figure of 835 species of
butterflies from northeastern India including Sikkim, Bhutan and Assam up to
Chittagong. However, information on
butterflies of Bhutan as such is scanty. A booklet published by van der Poel & Wangchuk (2007) on butterflies of the Bhutan mountains, hills and valleys between 800–3,000 m lists
only 136 species from the country. van der Poel & Wangchuk (2007) does not include butterflies from subtropical
low land forests of Bhutan lying below 300m, which are contiguous with forests
in India and are considered rich in terms of biodiversity. One estimate for Bhutan puts the figure
between 800–900 species with the largest number being found in the
‘subtropical’ zone (van der Poel & Wangchuk 2007).
The
present work on butterflies is part of the environment impact assessment
studies undertaken on biodiversity of the influence (downstream) and impact
zone (upstream) for a proposed dam to be built by India, near Kerabari (26044’93N & 89055’55E),
in Bhutan, under the Sankosh Hydro-electric Power
Project (Images 1 & 2).
MATERIAL AND METHODS
Study Area
The
study area falls in the subtropical forests in the southwesternmostpart of Bhutan in the south-central Dzongkhag (Sarpang District). These forests are broadly classified as semievergreenbut vary from almost totally deciduous on exposed dry slopes to almost totally
evergreen in the forest valleys. Adjacent to and east of the study area lies the PhibsooWildlife Sanctuary. The sanctuary
covers an area of 265km2 of unique dry shoreaforest ecosystem and conserves tropical fauna such as the Tiger Panthera tigris,
Elephant Elephas maximus,
Gaur Bos gaurus,
Golden Langur Trachypithecus geei, Indian Wild Dog or Dhole Cuon alpinus, Grey
Peacock Pheasant Polyplectron bicalcaratum, Rufous-necked
Hornbill Aceros nipalensis,
Wreathed Hornbill A. undulatus, Great HornbillBuceros bicornisand is the only protected area in Bhutan having Chital Deer Axis axis and natural salforests. PhibsooWildlife Sanctuary touches its border with India and is linked on its
southwestern end to the Buxa Tiger Reserve in West
Bengal, India ca. 100km to the south-east of the study site, in India, lies theRipu-Chirang Wildlife Sanctuary (RCWF; 89055’–90030’E
& 27015’–26035’N) in western Assam which is a
transitional zone between Manas Tiger Reserve in the
east and Buxa Tiger Reserve in the west. About 300 species of butterflies have
been recorded from RCWF including the rare Yellow-crested Spangle Papilio elephenorDoubleday, 1886 and Moore’s Cupid Shijimia moorei Leech, 1889 (Choudhury2010), although the list has not been given.
Sampling
Five
sampling surveys were carried out during 7–9 January 2009 (winter),
13–14; 17–19 May 2009 (pre-monsoon), 11–13 July 2009
(monsoon), 26–28 November 2009 (post-monsoon) and 19–22 March 2010
(spring) in the study area (Images 3–8). In January the day temperature and
relative humidity (11:30–15:30 hr) varied
between 23.6–27.8 0C and 57.4–58.4 %, respectively, with
days being short. During March
relative humidity varied between 57.1–60.1 % and day temperature between
33.4–34.2 0C. In
May the weather was hot and dry while during July (monsoon) the whole area
remained under cloud cover with high relative humidity (83–90 %) and
temperature (30.3-32.1 0C). At this time rain drizzled intermittently throughout the day while all
the road network between Kalikhola (26044’20N
& 89051’25E) and Kerabari was washed
out at places by running seasonal streams. During November the weather was cool and dry (relative humidity
61–62 %; temperature 26–27 0C) the weather at this time
being more comfortable to work in and the road network is also restored.
Transect
walks were undertaken along the road that links KalikholaVillage located on the Indian border to KerabariVillage (15km) and then further on a foot trail linking Kerabari-Huma Semal Village (6km) along the SankoshRiver and finally 5km further north upstream from Huma Khola on a foot trail. All the sampling sites lay on the right
bank of the river Sankosh between 118–220 m and
26044’21”–26047’69”N & 89051’25–89056’05”E. ‘Pollard Walk’ method used for sampling
butterflies was carried out throughout the day from morning (10:00 hr) until sunset (17:00–18:00 hr),
but the total number of sampling hours varied from 4–8 hr per day being less during the monsoon season
(July=3.5–4h/day) and maximum in the pre-monsoon
(May=7–8h/day). Thus, a total
of ca.110 hr of sampling was carried out during the entire
study period. Butterflies were
recorded up to 20m on both sides of the transect and on the river
bed of Huma Kholanear Huma Village. In addition, a transect (500m) uphill
along the forest stream which flows into the river Sankoshat the U-turn near Kerabari was also sampled by
trekking for a day (04 March 2011). During each season sampling was carried out for 3–4 successive
days at a stretch on these trails. Butterflies were identified mainly by taking photographs,
and using field guides for identification (Evans 1932; Wynter-Blyth
1957; D’Abrera 1982, 1985, 1986; Smith 1989, 2006; Haribal 1992; Kehimkar2008). Identification of some
species of the Neptis soma group (Nymphalidae) and the Telicotacolon group (Hesperiidae) was based on wing pattern
as captured in the images, and not based on the genitalia. Hence these might require confirmation.
Data Analysis
Species Accumulation Curve
Data
for the number of species recoded in each season was pooled. Species accumulation curve was then
plotted seasonally from the first to the last sampling to see the rate of
species accumulation during each of the five successive samplings.
Relative Abundance
The
abundance data for each butterfly species for all the five seasons combined was
pooled separately to get the overall relative abundance status of each
species. This data was then sorted
in descending order from highest to lowest value and species were then placed
in four different classes based upon their respective quartile divisions from
very common to uncommon, respectively i.e. VC - very common or Q1 (7–217
number of individuals sampled); C - common or Q2 (4–6); FC -
fairly common or Q3 (2–3); UC - uncommon or Q4 (1), respectively.
Student’s t-test
Relative
abundance data of ‘very common’ species (Q4; n=48) of butterflies for
individual seasons (n=5) was then subjected to ‘paired t-tests’ (both
two-tailed and one-tailed) to see if the seasonal variations between two
different seasons were significant at p< 0.05 using SPSS 14
software. [Data was tested for
normality prior to analysis and non-parametric tests were followed accordingly
to look at the variations].
Simpson’s Index
As
species richness and evenness increase, diversity increases. ‘Simpson’s Diversity Index’ takes into
account both richness and evenness (Evenness is a measure of the relative
abundance of the different species making up the richness of an area). ‘Simpson’s Index of Diversity’ was
calculated and used here to see the seasonal variation /trend in species
diversity of butterflies in the lowland forests of Bhutan. Simpson’s Index (D) (Simpson 1949) measures
the probability that two individuals randomly selected from a sample will
belong to the same species (or some category other than species).
D
= ∑ n(n-1)/N(N -1)
n = the total number of
organisms of a particular species
N = the total number of organisms of all species
The
value of D ranges between 0 and 1. With this index, 0 represents infinite diversity and 1 no
diversity. That is, the bigger the
value of D, the lower the diversity. As this is neither intuitive nor logical, to get over this problem, D
was subtracted from 1 to give Simpson’s Index of Diversity = 1–D. The value of this index also ranges
between 0 and 1, the greater the value, the greater the sample diversity. In
this case, the index represents the probability that two individuals randomly
selected from a sample will belong to different species.
Sørensen’s Similarity Index
This
index or ß was calculated to see the species similarity of butterflies between
different seasons in lowland forests.
ß
= 2c / (S1 + S2)
Here,
S1= the total number of species recorded in one season, S2= the total number of
species recorded in a different season, and c=the number of species common to
both the seasons.
TheSørensen’s similarity index (Sørensen1948) is a very simple measure of beta diversity, ranging from a value of 0
where there is no species overlap between the communities, to a value of 1 when
exactly the same species are found in both communities.
RESULTS AND DISCUSSION
A
total of 213 species of butterflies were recorded during the five sampling
surveys carried out in 18 days in the study area. A complete checklist of butterflies
sampled in the study area is given in the Table 1). Amongst these, only 87 species are
common with van der Poel & Wangchuk(2007) list for areas between 800–3,000 m in Bhutan.
Species accumulation curve
The
increasing trend in the species accumulation curve shows that new species were
added during every season up to the last sampling at about the same rate (Fig.
1). This suggests that there is a
potential of adding more species to the current list of the area and there is a
need to undertake more surveys for a preparing an exhaustive list.
How many species could be
there in the study area?
A
total of 22 species of the family Papilionidae were
recorded in this which suggests that the species richness of the area could be
as high as 297 species based on family proportion model (Singh & Pandey 2004) by taking Paplionidaespecies proportion as 7.4% of the total for northeastern India (Wynter-Blyth 1957). The present findings thus represent only 70.6% of the species found in
the study area. The family Pieridae represents only 10.8% of the total; Lycaenidae 24.0%; Nymphalidae42.4% and Hesperidae 13.3%, respectively, of the
total species sampled. As per Singh
& Pandey (2004) model, families Lycaenidae and Hesperiidae should
represent 29.5% and 21.9%, respectively, of the total number of species sampled
in northeastern India. These two
families are thus under represented in the present sampling and there is a need
to look for more species.
Seasonality of butterflies in
subtropical lowland forests
Species richness and diversity: The seasonal variation in
Simpson’s Index of Diversity (Fig. 2) and the number of species sampled during
each season (pooled data; Fig. 3), suggests that species diversity and richness
both peak during March (spring) and are lowest in January (winter). A second peak was observed during November which was smaller than the first peak. This seasonal pattern of diversity in
butterflies is very typical of the lower foothills and valleys of the Himalaya,
i.e. Dehradun Valley (400–700 m) (Singh & Bhandari2003) or even Calcutta (Wynter-Blyth 1957). However, the timing of the two seasonal
peaks, as observed in this study, is slightly different in pattern as compared
to the butterflies found in the higher reaches of the Himalaya where the first
peak is slightly late in April–May while the second peak is slightly
earlier in September–October i.e. Bhutan between 1,200–3,000 m (van
der Poel & Wangchuk2007) or Shimla at around 2000m (Wynter-Blyth
1957). This is because spring
arrives late in the higher reaches so butterflies emerge later and as winter
sets in early in the hills, so butterflies go into hibernation early as
compared to the low land forests.
Species similarity between seasons: Sørensen’s similarity index between
seasons varied between 0.3076 to 0.5656. This suggests that the species
composition also changed with the seasons in these forests. Greatest species
similarity was observed during January and November followed by March and November,
respectively (Fig. 4). However, the
least species similarity in species composition was observed between January
and July followed by January and May, respectively (Fig. 4).
Relative abundance: The five most abundant
species in the study area were Euploea mulciber mulciber, Ixais pyrene pirenassa,Appias lyncida hippoides, Tirumala septentrionis and Eurema blanda silhetana. The seasonal variations in relative
abundance of butterflies for ‘very common’ species (n=48; Q4) were found to be
significant (p< 0.05; Student’s t-test) between only
January–March; March–May and March–November. Thus, the abundance of common
butterflies during ‘spring’ varied significantly as compared to ‘winter’, ‘dry
summer/pre-monsoon’ and ‘post-monsoon’ seasons.
Species of conservation priority: At least 11 species (Pareronia avatar avatar,Nacaduba pactolus continentalis, Porostas aluta coelestis, Lampides boeticus, Melanitis zitenius zitenius, Elymnias vasudeva vasudeva, Mycalesis mestra retus, Charaxes marmax, Athyma ranga ranga, Neptis manasa manasa and Neptis soma) recorded in the study
area have been listed in Schedules I and II of the Indian Wildlife (Protection)
Act, 1972 (IWPA), but none in the ‘Forest Nature and Conservation Act of Bhutan
1995’or IUCN Red list of Threatened species (IUCN 2010). Amongst these 11 species, except for Lampides boeticus , all other taxa are ‘rare’ throughout their distribution
range (Evans 1932; Wynter-Blyth 1957) and are thus
species of conservation priority over rest of the other taxa in the study
area. Besides, one more species, Burala amara Moore,
which has been omitted from the IWPA, is also a ‘rare’ species in India (Evans
1932).
CONCLUSION
High value of ‘Simpson’s index ’ (0.8929–0.9687) points to
the area having high variation. A
stretch of ca. 12km monitored during the 18-day sampling revealed as many as
213 species and had the potential of adding many more species. The list provided here is in no way
complete but represents ca. 2/3 species found in these tracts in the study area
and ca. ¼ of the species estimated from Bhutan. Besides, 12 taxa that are ‘rare’ in
occurrence throughout their distribution range and worthy of conservation were
also recorded in this subtropical lowland forest tract. Also, a good number of butterfly species
were present during all the five seasons (93±12 species per season; range =
66–129 species) which is a good indicator of the
potential of this area for butterfly ecotourism, that needs to be
explored. ‘Biodiversity offsets’
such as butterfly conservatories or even a butterfly park can be established
here for conserving the ‘rare’ species and promoting ecotourism. Thus, the present study is a way forward
to bridge the remaining gaps today in documenting the complete butterfly fauna
of the area, identifying sites and species of conservation concerns in the
subtropical lowland forests of Eastern Himalaya.
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