Discussion
This is the first comprehensive survey of leopard occupancy covering the
entire Chure range (18982 km2) of Nepal. We found the
spatial replicate model performed better than the standard occupancy
model (supplementary 1). Our result showed that more than half of the
Chure range was occupied by leopards. The leopard occupancy was
primarily associated with the presence of wild boar (one of the prey
species), human population density, terrain ruggedness and the presence
of livestock. The detection probability of the leopard was higher
outside the protected areas, less in the densely vegetated areas and
higher in the areas with the presence of livestock.
The reliability of the occupancy is dependent on the detection
probability of the leopard sign on the replicates (Hines et al., 2010).
The value of naïve estimate occupancy (0.31) through the conventional
presence-absence approach created biased in the actual occupancy because
it did not consider the false absences (Fig 3). The prior consideration
of leopard home range, their behaviour, the prior identification of
associated covariates while designing the survey, and formation of the
representative global model has helped us to obtain robust detection
function and explain the pattern of leopard occupancy as well as
associated environmental and ecological factors (Karanth et al., 2011).
In our result, the probability of leopard presence on
1st level replicate was more than the probability of
leopard presence in a replicate occupied and which was absent in the
previous replicate (θ0). Similarly, the leopard presence
on a replicate was higher when the previous replicate was occupied
(θ1) by the leopard. The result was consistent to
Barber‐Meyer et al., 2013.
The probability of leopard occurrence in the Chure range in Terai Arc
Landscape (TAL) (between Parsa National Park (PNP) in the east and
Shuklaphanta National Park (ShNP) in the west (Fig 1, 2) was higher.
Within TAL, there are 5 national parks with source populations of
leopards. Leopards are highly adaptable in terms of foraging strategy
and flexible for habitat selection in the rugged Chure area (Balme et
al., 2007; Dutta et al., 2013). Similarly, all 5 national parks are the
home for tiger, the apex carnivore. The tiger focused conservation
activities in these protected areas has increased their number nearly
twice since 2010 (DNPWC & DFSC, 2018). The increasing number of tigers
in these national parks may have pushed leopards to the adjacent Chure
range (Odden et al., 2010; Thapa & Kelly, 2017; Lamichhane et al.,
2019a). Compared to protected areas, the Chure forests outside has a
lower density of prey (Shrestha, 2004). Leopard probably avoids
interspecific encounters with tigers by choosing these marginal areas
(Woodroffe & Ginsberg, 1998; Lamichhane et al., 2019a). Besides the TAL
area, in the eastern part of Nepal, there is only a small protected
area, i.e. Koshi Tappu Wildlife Reserve (area: 175 sq km) which touches
a small portion of the Chure range in the north (Fig 1). Due to this,
the wildlife conservation activities are low in the eastern part.
Similarly, the average forest cover in the central, western, and
far-western grid of the Chure range is greater than the eastern grid. It
may have reduced the prey availability and subsequently reduced the
leopard occupancy in the eastern part compared to the TAL area. Hence,
this study of leopard occupancy distribution helps wildlife managers and
policymakers to guide for identifying locations to focus on leopard
conservation in the Chure range.
Our results did not correspond to earlier findings that the leopards
avoid wild boars (Eisenberg & Lockhart, 1972; Ramakrishnan et al.,
1999; Hayward et al., 2006). In our study, it positively influenced the
leopard occupancy in the Chure range. The leopard consuming wild boar as
a diet was also observed by (Kandel et al., 2020) in the Kamdi forest
corridor of the western part of the Chure range. The wild boar occurred
in almost half of the surveyed grids in the Chure range, the highest
among the mammal species surveyed. Leopard and wild boar co-occurred in
49 (22%) grids. (Karanth, 1999) also reported the occurrence of the
leopard proportional to the wild boar. Our study showed the importance
of wild boar as prey species on the occurrence of leopard. Some previous
studies excluded prey species in their analysis which could have biased
the result (Gavashelishvili & Lukarevskiy, 2008; Maharjan et al.,
2017).
We also used other prey species (Barking Deer, Rhesus, and Chital) as
covariates but their influence in the model was weak. Scarcity of prey
other than wild boar in the Chure range could be the reason for this.
The opportunistically placed camera traps along with this survey also
photographed poachers with guns in various locations. It indicates the
widespread hunting of wild prey species which have probably contributed
to reducing the prey abundance.
The positive influence of the ruggedness index on leopard occupancy
indicates the extensive use of rugged Chure hills by leopards. The
rugged terrain provides an opportunity for ambush predators to hunt
(Sharma et al., 2015). Leopards are excellent climbers and rugged
terrain probably does not limit their movements/ use of the habitat.
Generally flat and less rugged areas are occupied by human settlements
and the rugged hills are still covered with forest providing habitat for
leopards, their prey and other wildlife. However, we didn’t find the
relation between vegetation cover (NDVI) and leopard occupancy. Instead,
the detection probability was inversely related to NDVI. In intact
forests (high NDVI value) generally, there are fewer and less visible
animal trails. Detecting the leopard sign in such a forest is
comparatively difficult which reduces the detection probability. The
survey was conducted in the post-monsoon season, the time the leaves
start shading from the deciduous trees. The fallen leaves covering the
forest floor also reduces the chances of detecting the leopard sign in
densely vegetated areas.
We found the positive influence of human population density and
livestock on leopard occupancy. It indicates that leopards can persist
in the highly modified landscape with high human population density. The
findings correspond to (Athreya et al., 2013, 2016; Kuhn, 2014). The
majority of the Nepalese rural community is based on agriculture and
livestock is an integral part of their farm (Lamichhane et al., 2019b).
Thus, livestock can be used as a proxy of human pressure in this
landscape. Livestock was present in ~55% of the
surveyed grid and leopard occurred in 19% of the grids with livestock
presence. It increases the chances of livestock encounters by leopards.
Leopards may be depending potentially for their diet in the livestock
(Kandel et al., 2020).
Leopards are specialized solitary hunters primarily hunting wild
ungulates, but also kill livestock if opportunity arises (Treves &
Karanth, 2003; Kandel et al., 2020).In the presence of the sufficient
natural prey base, leopards tend to avoid livestock (Kolowski &
Holekamp, 2006). We do not have the data on the density of prey in the
Chure range but the low detection of prey signs (except the wild boar)
indicates their low abundance (Smallwood & Fitzhugh 1995; Stander,
1998). In absence of enough wild prey leopards shift to livestock for
diet (Khorozyan et al., 2015) which is also observed in our study with
the positive influence of the livestock on leopard occupancy. So, this
opportunistic predator may have followed the optimal foraging theory to
minimize their search time, encounter rates and the energy cost to
capture prey (Sunquist & Sunquist, 1989; Lamichhane & Jha, 2015). It
indicates the possibilities of human-leopard conflict in the Chure
range. We suggest that maintaining a sufficient natural prey base can
contribute to minimize the livestock depredation and hence, decrease the
human-leopard conflict in the Chure range. Similarly, the detection of
the leopard sign was higher in the Chure range that falls outside the
protected areas. It may be because the vegetation cover (NDVI) inside
the national park is high in comparison to the outside area which
reduces the chances of leopard sign detection.
More than half of the Chure range is occupied by leopards. We identified
wild boar, human population density, ruggedness and livestock presence
as top covariates influencing their occupancy that would support the
policymakers, researchers, and wildlife managers to search possibilities
to increase the leopard occupancy in the range. The grid wise occupancy
estimate provides insight to identify the area that needs conservation
actions. The positive influence on the occupancy of leopard with the
presence of wild boar and livestock has indicated the importance of wild
ungulates and pointed the possibilities of human-leopard conflict. The
activities focusing to increase the wild prey base in the Chure range
through better protection would help to reduce the livestock depredation
by leopards and their retaliatory killing.
Sign based occupancy survey is a suitable method for landscape-level
studies of large-ranging species like leopards. We recommend carrying
out an occupancy survey in the Chure range periodically to understand
leopard status as done for tigers in TAL. In future research, the
exploration of the livestock depredation and human-leopard conflict data
add value to understanding the dynamics of the conflict.