Journal of Threatened Taxa | www.threatenedtaxa.org | 26 October
2019 | 11(13): 14655–14662
Current population status of
the endangered Hog Deer Axis porcinus
(Mammalia: Cetartiodactyla: Cervidae)
in the Terai grasslands: a study following political
unrest in Manas National Park, India
Alolika Sinha 1, Bibhuti Prasad Lahkar 2
& Syed Ainul Hussain 3
1,2 Aaranyak, 13, Tayab Ali Byelane, Bishnu Rabha Path,
Guwahati, Assam 781028, India.
1,3 Wildlife
Institute of India, Post Box 18, Chandrabani,
Dehradun, Uttarakhand 248001, India.
1 sinha.alolika@gmail.com
(corresponding author), 2 bplahkar@gmail.com, 3 hussain@wii.gov.in
doi: https://doi.org/10.11609/jott.5037.11.13.14655-14662
Editor: David Mallon, Manchester Metropolitan University,
Derbyshire, UK. Date of publication: 26 October
2019 (online & print)
Manuscript details: #5037 | Received 01 May 2019 |
Final received 01 October 2019 | Finally accepted 05 October 2019
Citation: Sinha, A., B.P. Lahkar & S.A. Hussain (2019). Current population status of the endangered Hog Deer Axis
porcinus (Mammalia: Cetartiodactyla:
Cervidae) in the Terai
grasslands: a study following political unrest in Manas
National Park, India--. Journal of Threatened Taxa 11(13): 14655–14662. https://doi.org/10.11609/jott.5037.11.13.14655-14662
Copyright: © Sinha et al. 2019. Creative Commons Attribution
4.0 International License. JoTT allows unrestricted use, reproduction, and
distribution of this article in any medium by adequate credit to the author(s)
and the source of publication.
Funding: Ocean Park Conservation
Fund Hong Kong (OPCFHK), U.S. Fish and Wildlife
Service (USFWS) and Auckland Zoo Conservation
Fund.
Competing interests: The authors declare no competing
interests.
Author details: Alolika Sinha is a wildlife biologist working with an NGO Aaranyak in Assam and a PhD Scholar with Wildlife Institute
of India. Her research interest includes population and habitat ecology. She is
currently working on hog deer and grassland conservation projects in Assam. Dr. Bibhuti Prasad Lahkar is a conservationist, working with Aaranyak. For his PhD, he studied the ecology and
management of grassland ecosystem in Manas. He has
successfully implemented many conservation projects in northeast India and has
been awarded with “Heritage Heroes Award” by IUCN WCPA in 2016. Dr. Syed Ainul
Hussain, is Scientist-G and a professor working with Wildlife Institute
of India. He has many scientific
publications to his credits and members of many esteemed organisations/commissions.
Author contribution: AS, BPL and SAH developed the
concept and designed the framework. SAH provided valuable inputs in statistical
analysis and manuscript writing. AS and BPL acquired the resources. AS
collected data, performed statistical analysis and interpretation, manuscript
writing and revisions. BPL and SAH supervised the project and contributed to
the manuscript.
Acknowledgements: We would like to thank Assam Forest Department and Manas Project Tiger Directorate for providing necessary
permission to carry out the study. We are grateful to Ocean Park Conservation
Foundation, Hong Kong, Auckland Zoo Conservation Fund, New Zealand and USFWS
for financially supporting the study. We thank Mr. Arup Kumar Das of Aaranyak for preparing the maps. We sincerely acknowledge
Mr. Qamar Qureshi (WII) for his valuable inputs in study design, data analyses
and interpretation. Our sincere thanks to Sunny, Ayan
and Anumitra for their support and cooperation. We
are also indebted to Krishna and Rohan, the field assistants and all the
Mahouts of Manas National Park, without whose active
participation the survey would not have been possible. We also acknowledge the
reviewers for their valuable comments in the manuscript.
Abstract: The Endangered Hog Deer Axis porcinus
has experienced drastic population declines throughout its geographical
range. There is limited knowledge of its
current population status, particularly from northeastern
India. In this study the population
density of Hog Deer was assessed in Manas National
Park, which was a deer stronghold prior to the armed conflict that lasted for
almost two decades, resulting in depressed deer populations. With the cessation of conflict, efforts were
invested by both government and conservation organisations for the recovery and
conservation of charismatic fauna in the park.
Studies on Hog Deer populations, however, were lacking and thus reliable
information on current status is unavailable.
Current population status and threats faced by Hog Deer were assessed to
aid informed conservation decisions.
Distance sampling techniques (line transects) were applied in the
grassland habitat during the dry season of two consecutive years. The estimated Hog Deer density was 18.22±3.32
km-2. The potential threats
to Hog Deer identified in Manas include habitat loss,
habitat degradation due to spread of invasive plant species, illegal hunting,
and other anthropogenic disturbances.
Our study suggests that the Hog Deer population, though reviving, needs
immediate conservation attention.
Keywords: Armed conflict, geographical range, invasive species,
population density.
INTRODUCTION
The Hog Deer Axis porcinus, historically distributed across South and
Southeast Asia, underwent a drastic range-wide decline during the mid and late
20th Century (Brook et al. 2015; Timmins et al. 2015). Subsequently, A. porcinus
was categorised as an Endangered species by the IUCN in 2008 (Timmins et al.
2015). Despite being an Endangered
species, it is one of the least studied mammals and its range-wide decline was
mostly overlooked (Brook et al. 2015).
The southeastern Asian population is locally
extinct in most countries, including China, Lao PDR and Vietnam (Ohtaishi & Gao 1990); the only wild populations remain
in Cambodia and Myanmar (Brook et al. 2015; Lwin et al. 2016). In southern Asia, with a declining population
trend, the Hog Deer is mostly confined to protected areas (Karanth
& Nichols 2000; Biswas 2004; Odden et al.
2005). Timmins et al. (2015) recommended
that estimating population abundance was important in assessing the
conservation status of A. porcinus. Though deer population estimates are
available for few well-managed protected areas, mostly in Nepal (Odden et al. 2005; Bhattarai & Kindlmann
2012; Lovari et al. 2015), data from other areas of
southern Asia are lacking.
The Hog Deer (Image 1) is a
grassland obligate (Dhungel & O’Gara 1991; Odden et al. 2005), primarily threatened by habitat
degradation or loss and illegal hunting.
It is an important prey for large carnivores (Stoen
& Wegge 1996; Lovari et
al. 2015), and thus plays a vital ecological role. India is one of the strongholds of A. porcinus populations in southern Asia, although
historically it has received little attention and available information is
mostly anecdotal (Biswas 2004). To
implement rational conservation measures, reliable estimates of population
abundance are fundamental, and their lack can undermine the entire process
(Lopez-Bao et al. 2018). Thus the
current population status of A. porcinus was
assessed and potential threats to the population in Manas
National Park in Assam were documented.
Manas National Park (henceforth, Manas) in northeastern India
harboured a population of approximately 10,000 Hog Deer until the 1980s (Tikader 1983), and armed conflict in the region from the
mid-1980s to 2003 lowered the population density (Goswami
& Ganesh 2014). The instability
resulted in habitat degradation, destruction of park infrastructure and
poaching/hunting in the absence of normal law and order. With the restoration of peace, conservation
efforts were implemented to safeguard remaining wildlife populations (UNESCO
2005). The cessation of civil unrest
facilitated access to Manas by various conservation
organisations that work with management authorities to conserve wildlife and
promote species recovery. Most of the
management and conservation inputs have focussed on securing and conserving
charismatic megafauna like One-horned Rhinoceros Rhinoceros
unicornis and Bengal Tiger Panthera
tigris, which are apex species in the ecosystem
and iconic species for conservation. In
comparison, lesser-known mammals like the Hog Deer have received little
attention. With about 40% grassland
habitat (Das 2018), Manas represents one of the last
remnant patches in western Assam that can support grassland obligates such as
One-horned Rhinoceros, Hog Deer, Hispid Hare Caprolagus
hispidus, Pygmy Hog Porcula
salvania, Bengal Florican Houbaropsis
bengalensis, Swamp Deer Rucervus
duvaucelii, Asiatic Water Buffalo Bubulas arnee, and
others (Lahkar 2008).
These grasslands are under threat from invasion by alien plant species,
mostly by Chromolaena odorata
and Mikania micrantha (Lahkar
et al. 2011; Nath et al. 2019), agricultural encroachment, and cattle grazing (Sarma et al. 2008), which may have had an impact on Hog
Deer population abundance.
It is evident that Hog Deer and
their habitat in Manas deserve immediate conservation
attention. Goswami
& Ganesh (2014) attempted to estimate the population density of herbivores
immediately after the cessation of the conflict, but their study had limited
observations. The authors conducted line
transect sampling on foot, which may have an influence on the detection
probability (Wegge & Storaas
2009). This is the first intensive study
from Assam that focussed on estimating the population density of Hog Deer. This provides an important insight regarding
the current status of this threatened species and the need for management
intervention for its long-term conservation.
MATERIALS
AND METHODS
Study area
The study was conducted in Manas National Park (26.7220N & 91.0430E),
which forms the core of the Manas Tiger Reserve in
the northeastern Indian state of Assam (Figure
1). It lies along the foothills of the
Himalaya, and is contiguous with the Royal Manas
National Park of Bhutan to the north, bounded by villages to the south, by Daodhara and Batabari reserve
forests to the east, and reserve forests to the west. The park comprises an area of 519km2
(Sarma et al. 2008) and has a predominantly flat
terrain. Broadly, the vegetation of Manas is classified as sub-Himalayan alluvial
semi-evergreen forest, east Himalayan mixed moist and dry deciduous forests,
the commonest type, and grasslands (Champion & Seth 1968). The grasslands are further classified into
dry savannah grasslands and wet alluvial grasslands. These grasslands occur in seven major grass
assemblages which harbour many threatened grassland obligates (Lahkar 2008). Manas harbours a rich faunal assemblage, with 60 species of
mammals, around 470 avian species, and 42 species of herpetofauna. The climate of Manas
is warm and humid, with rains from mid-March to October; most rain falls during
the monsoon months from mid-May to September and November to February is
relatively dry (Borthakur 1986).
In Manas,
political stability was attained with the formation of Bodoland Territorial
Autonomous Districts (BTAD) in 2003, and subsequently the conservation
intervention gained momentum, such as with a Rhino restocking programme (Barman
et al. 2014). Nevertheless, instances of
occasional conflicts were prevalent in the western Range (Panbari)
until 2016 (Lahkar et al. 2018). Therefore, the study was restricted in the
central (Bansbari) and eastern (Bhuyanpara)
administrative ranges of the park which had one such incident in 2014.
Field Survey
The population density of Hog
Deer was derived through distance sampling (Buckland et al. 2004), which is
established as a standard method and has been adopted widely to generate
herbivore densities across various habitats in the tropical and temperate
ecosystems in Asia (Varman & Sukumar 1995; Khan et al. 1996; Biswas & Sankar 2002; Jathanna et al.
2003; Wegge & Storass
2009; Wang 2010; Bhattarai & Kindlmann 2012; Goswami & Ganesh 2014; Lovari
et al. 2015). The entire study area was
overlaid with 2 x 2 km grid and stratified random sampling was adopted. Line transect surveys from elephant back (Wegge & Storaas 2009) were
conducted in the grids with grassland cover as the species is a grassland
obligate (Dhungel & O’Gara 1991; Odden et al. 2005) during the dry season of 2014–15
(henceforth, 2015) and 2015–16 (henceforth, 2016). A total of 75 transects were sampled,
covering a total distance of 206.56km.
Spatial replicates were used, as Hog Deer sightings were relatively low
in Manas (Krishna et al. 2008) and transect lengths
varied from 2 to 5 km. During the
elephant transects, the Mahout (elephant driver) and one observer detected and
counted the animals. For each detection
the radial distance of the animal to the observer and sighting angle were
measured using a range finder and a compass respectively.
Data Analysis
Initially, the encounter rate of
Hog Deer per transect per year was compared to investigate whether there is any
significant difference between them using a Z-test. As there was no significant difference
between both years (z=0.05, P > 0.05, n1= 35, n2 =40), the data from two
consecutive years were pooled to estimate the Hog Deer population density in
the park using programme DISTANCE 7.1.
Conventional distance sampling (CDS) approach in DISTANCE programme was
used to derive Hog Deer density estimates (Buckland et al. 2001). Exploratory analyses were carried out to
check for evasive movement before detection, heaping effect, and truncation of
observation outliers (Buckland et al. 2001).
The data were grouped into unequal distance bins, and chi-square goodness-of-fit
values (the lowest) were considered to select the interval combination
(Buckland et al. 2004; Zamboni et al. 2015).
The data beyond the distance of 45m were truncated as they were outliers
for better model fitting. The
probability of detection was estimated using six models recommended by Buckland
et al. (2001) combining probability density function (uniform, half
normal and hazard-rate) with adjustments (cosines, simple and hermite polynomials).
The models were selected based on the criterion of lowest AIC as
generated by the program. The estimates
were generated with standard error, the coefficient of variation and confidence
intervals. Hog Deer density (D) was estimated,
and approximate population size (N) was computed based on the size of the
habitat area.
To derive the population
structure and age-sex-ratio of Hog Deer, intensive surveys were conducted in
the entire park and computed based on percentage sightings. Data were recorded both during the line
transect sampling and opportunistic sightings over a period of two years on
group size and composition. For each
detection, the animals were classified into the following age-sex categories;
fawn (1–12 months), yearlings (13–24 months) and adults (>24 months) based
on Dhungel & O’Gara (1991) classification. Based on the sightings, adult male to adult
female and doe to fawn ratio was calculated.
The data from both the years were pooled as there was no significant
difference between the adult male (z=0.49, P>0.05, n1=56, n2=68) and adult
female (z=1.65, P>0.05, n1=56, n2=68) categories between the years. Furthermore, a significant difference between
the percentage of adult male and female in a group was tested using z
statistic. The percentage data was
transformed using arcsine transformation and analysed using MS Excel.
RESULTS
A total of 202 sightings of Hog
Deer were made along the 206.56km of transects during the two years sampling
period. Of these, 56.20% of the
sightings were from the central range and 43.80% from the eastern range. The overall density of Hog Deer in Manas was estimated to be 18.22 ± 3.32 km-2 (CV
= 18.27%, 95% CI = 12.72–25.09). Based on comparisons of the lowest AIC values,
the uniform key function with cosine adjustment best described the Hog Deer
data (Figure 2). The result, with
estimated density, percent coefficient of variation, 95 % confidence interval
and AIC is summarised in Table 1. On
extrapolating the population density of 18.22km-2 to the available
grassland habitat in the park (194.57km2, Das 2018), the population
size of Hog Deer was estimated to be 3,545 ± 647.64 (CV = 18.27%, 95% CI =
2,475–5,077).
To understand the age structure
of Hog Deer population, the percentage of different group types was calculated
based on the number of animals detected during the line transect and other
opportunistic sightings for both the years.
In a few instances (4.59%), though, the sex of the animal could not be
identified. The groups were classified
as solitary-consisting of single animal, small (2–3 animals), medium (4–6
animals) and large (>6 animals) groups (modified from Biswas 2004). Most of the animals occurred solitary
(50.79%), 36.50 % occurred in small groups, 10.31% in medium groups, and only
2.38% in large groups. The mean group
size of Hog Deer is estimated to be 1.81 ± 0.11. The observed overall sex ratio in Manas, of adult male to adult female to fawn is
47.01:100:17.88. There is a significant
difference between the adult male and female percentage in a group (z= 4.72,
P<0.01, n1=n2=125).
DISCUSSION
Our study suggests that the
current estimated Hog deer density in Manas differs
substantially from that of the previous study which reported a density estimate
of 4.59km-2 (Goswami & Ganesh
2014). One of the possible reasons is
the difference in the line transect sampling method that the two studies have
adopted. Sampling in grassland habitats
on foot may influence the detection probability and underestimate the
population abundances of species like Hog Deer (Wegge
& Storaas 2009).
Therefore, we conducted line transect surveys from elephant back
following Wegge & Storaas
(2009), which may have led to higher Hog Deer density estimate than the
previous study. During the All India
Tiger Monitoring exercise, the attempt to estimate prey density in Manas with an effort of 134km was hindered due to low
number of observations (Jhala et al. 2015). The line transect sampling was conducted on
foot, which might have resulted in lesser sighting records due to tall and
dense vegetation. Therefore, sampling
from elephant back in the grassland habitat in Manas
is recommended for all the future population estimates of Hog Deer. In this study the estimated population size
of Hog Deer is 3,545, considerably different from the previous estimate of
1,626. The sampling protocol to used
derive this estimate was not clear.
Nonetheless, our study finding indicates a possible recovery of the Hog
Deer population over the years with the cessation of the conflict which can be
attributed to enhanced protection and anti-poaching measures.
The Hog Deer population in Manas is female-biased.
The sex ratio favouring the females is a characteristic of polygamous
species (Dhungel & O’Gara 1991). Seidensticker
(1976) reported a sex ratio of 51 males: 100 females: 24 fawns, whereas Mishra
(1982) observed a ratio of 59 males: 100 females: 55 fawns. A similar sex ratio was also observed by Dhungel & O’Gara (1991) (56 males: 100 females). The mean group size of Hog Deer in Manas is similar to that of Chitwan (1.8, Dhungel & O’Gara 1991), but lower than reported in Jaldapara Wildlife Sanctuary (2.68, Biswas 1999). Hog Deer is primarily a solitary cervid (Odden & Wegge 2007), but congregates in small groups while
feeding. During our study period we
mostly documented Hog Deer singly or in small groups. Large groups comprising of more than six
individuals were observed less frequently (12.69%). Biswas (1999) reported that 41% of animals
were solitary, 56% occurred in small to large groups and only 3% occurred in
very large groups (>10 animals) in Jaldapara. The largest congregation observed was of 33
animals, feeding on the fallen flowers of Gmelina
arborea during the dry season in Manas.
Prior to the armed conflict, Manas harboured an abundant Hog Deer population of
approximately 10,000 animals (Tikader 1983). The absence of empirical data on Hog Deer
populations before and after the conflict limits our efforts to quantify the
population change; interactions with experts who have worked in the area during
the 1980s suggest that the population has declined sharply, more than 70%
(Goutam Narayan pers. comm. December 2017).
The local extinction of One-horned Rhinoceros (Talukdar 2003), depressed
population of Swamp Deer (Das et al. 2009; Borah et al. 2013), Pygmy Hog (Bibhuti P. Lahkar pers. obs.
19.xii.2017) and Bengal Florican (Namita Brahma pers. comm. 19.xii.2017) due to
the armed conflict (Lahkar et al. 2018), reflects
that the grassland species declined drastically because of selective hunting by
both opportunistic hunters and the anti-government forces (Goswami
& Ganesh 2014). The possible drivers
of Hog Deer decline are habitat degradation & reduction and illegal
hunting. The grasslands which Hog Deer
prefer have reduced in area over the last four decades (Sarma
et al. 2008; Das 2018). The grassland
patches such as ‘Pahufield’ area, ‘Rhino camp’ area
and the grasslands particularly near the southern boundary of the park, mostly
in the central range, which were prime Hog Deer habitats (Bibhuti
P. Lahkar pers. obs. February 2002) are heavily infested
with invasive plants such as Chromolaena odorata and Mikania micrantha
(Nath et al. 2019). There is also
livestock grazing pressure in the grassland (approximately 2000 cattle per day
graze inside the park during the dry season, (Alolika
Sinha pers. obs. 20.iii.2017) and can lead to severe competition for forage.
Trapping of Hog Deer for
consumption using snares in the fringe village is not uncommon (Alolika Sinha pers. obs. 25.iii.2017). During the study period, four incidents of
Hog Deer hunting were recorded in the fringe villages. This may underestimate
hunting incidents, since many go unreported.
We also found snares along the southern boundary of the park, which were
possibly set-up to trap Hog Deer, other small mammals (e.g., hares), and birds.
Another emerging threat to the species in Manas is
attack by feral dogs. During the dry
season, when the Hog Deer congregate to feed on Gmelina
arborea flowers and fruits in the central range
near an area called ‘second gate’, they are attacked by the feral dogs. We recorded six incidents over a period of
two months (February--March 2016) where the feral dogs attacked and killed
deer, although the dogs were not seen eating them. A multitude of factors like habitat
degradation, occurrence of invasive plant species, and anthropogenic
disturbances might affect the Hog Deer population in Manas. The influence of these various factors on Hog
Deer population can be drawn more conclusively, upon long-term monitoring of
its population and grassland habitat.
The present Hog Deer estimate,
when compared with those from other areas in southern Asia revealed that Manas is an area of intermediate deer density (Table
2). Nevertheless, with the restoration
of governance and administration, the management intervention improved
substantially. A major step was the
conversion of the former poachers/hunters into conservation volunteers and
engaging them in regular patrolling of the park along with the forest
personnel. Hog Deer are known to occur
in high density in other well-protected areas (Table 2) (Karanth
& Nichols 2000; Odden et al. 2005). The grasslands in Manas
are one of the last remnant habitats in the eastern Terai
(Lahkar 2008) and crucial for Hog Deer survival in the
region (Biswas 2004). The scope of Hog
Deer persistence beyond the National Park is limited due to scarcity of
potential habitats and high anthropogenic pressure on these habitats.
Our study highlights the current
population status of this threatened species, and we have documented potential
threats to Hog Deer in Manas. This baseline population estimate will be
useful to monitor future changes and conservation of Hog Deer in one of the
high-value conservation landscapes. Manas is the most promising potential habitat for long-term
survival of Hog Deer in western Assam, given that it is the best protected
grassland habitat in the region. To this
end, we suggest regular monitoring of Hog Deer populations and habitat
improvement to document population recovery with the minimisation of the extant
threats, and the formulation of future management strategies.
Table 1. Summary of overall Hog Deer density estimate
in six models as recommended by Buckland et al. (2001).
Parameter |
Uniform + Cosine |
Uniform + Simple polynomial |
Half normal + Cosine |
Half normal + Hermite polynomial |
Hazard rate + Cosine |
Hazard rate + Simple polynomial |
Density km-2 |
18.22 |
18.12 |
18.86 |
18.86 |
17.57 |
17.57 |
Percent Coefficient of variation |
18.27 |
19.07 |
19.26 |
19.26 |
20.14 |
20.14 |
Upper CI |
25.09 |
26.25 |
27.51 |
27.51 |
26.06 |
26.06 |
Lower CI |
12.72 |
12.50 |
12.93 |
12.93 |
11.84 |
11.84 |
AIC |
375 |
376.79 |
375.07 |
375.07 |
376.54 |
376.54 |
Figure
figures & image – click here
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