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Occupancy and abundance of tigers and their prey in the Terai Arc landscape, Nepal

Occupancy and abundance of tigers and their prey in the Terai Arc landscape, Nepal
Jhamak Bahadur Karki


Wildlife Institute of India, Forest Research Institute, Dehradun, 248 006, INDIA.


Nearly 3,500 wild tigers (Panthera tigris Linnaeus 1758) occur in Nepal as well as 12 other range countries in Asia. In Nepal, they are restricted in isolated Chitwan - Parsa, Bardia - Khata and Suklaphanta populations in a land base of about 4,700 km2 of National Park, buffer zone and corridor forests where the prey densities are still high in few Protected Areas (PAs).

Camera trap was used in the past to document the minimum tiger numbers but the estimation of more realistic number is crucial when number declined to two fifth of its population in the last decade (1996-2006).

The occupancy, distribution and tiger density are important information for management and conservation policy formulation. Realizing this need, this study was undertaken.

The major wild prey species of tiger are spotted deer (Axis axis), wild pig (Sus scrofa), sambar (Rucervus unicolor), swamp deer (Rucervus duvaucelli duvaucelli), barking deer (Muntiacus muntjak), hog deer (Heylaphus porcinus) and gaur (Bos gaurus) in Nepal.

To evaluate the occupancy of tiger in Nepal's Terai Arc landscape (TAL), sign survey was conducted in 96 grids (area 225 Km2) in 14 districts, including PAs. To assess correlation of the tiger occupancy with the availability of wild prey, and the human disturbance with the habitat use by the tiger, the sign of human disturbances (fire, timber cut, fuel wood collection, sign of poaching) and prey presence were recorded during the winter season.

To estimate the density of tigers wild prey in PAs of Nepal's TAL, distance sampling was conducted along the predefined line transects during the summer season.

To estimate the abundance of tigers in PAs of Nepal's TAL, passive camera traps were employed during the dry season.

Use of the area by tiger was higher in prey rich areas with lower human disturbances. Prey depletion has been recognized as an important factor driving the current decline of wild tiger populations and hence a significant constraint on their recovery. Therefore, to increase tiger occupancy, otherwise suitable areas that have low prey bases should be managed with an important focus on increasing the primary prey base for tigers. Tiger occupancy was mainly influenced by large sized prey such as sambar, swamp deer, rhino, gaur and chital in PAs whereas by chital and wild pig outside, indicating that the conservation of large sized prey would help build tiger occupancy in tiger habitats outside PAs. Monitoring larger area with lower cost by using existing experienced technicians with nominal training provided a reasonable indication of the use of area by tiger. This result clearly indicated need for management intervention to improve the habitat conditions and also to reduce the human induced pressures in critical tiger habitat.

Availability of ungulate predicts the possibility of tiger availability. The higher tiger abundance in Chitwan National Park (CNP) with effective protection had shown stable tiger population in two consecutive years. Use of Churia habitat by tiger was documented and was possible due to the availability of wild ungulate in Churia. The tigers of CNP share the range with Parsa Wildlife Reserve (PWR). As the tiger status seems improving in CNP, the PWR would receive the tigers. The habitat management, waterhole development and stringent protection would help improve the status of prey base and thereby the tigers in PWR.

Though the wild prey base is reasonably high in Bardia National Park (BNP), about 50% of the tiger’s number declined over a decade. The reason could be poaching and reduction of prey base during the insurgency period. The overall improved protection, declaration of 180 Km2 of buffer zone towards north and establishment of Banke National Park (BaNP) towards east has increased the legal protection of the area and provided the working opportunity with people. The upgraded status of Khata corridor by Government of Nepal (GoN) and functional use of the corridor by tiger with Katarniaghat Wildlife Sanctuary generate immense hope that the tiger number could come back to what was there a decade ago. This would require consistent intelligence, networking and youth involvement program in Khata corridor. Action should be initiated to enhance the prey status after assessing the prey base in BaNP and locating functional movement route of tigers from BNP to BaNP to facilitate the tiger movement and longer use leading to establishment in the newly declared BaNP.

The wild prey base is high in Suklaphanta Wildlife Reserve (SWR), where tiger’s population declined to about 60% in 8 years. The potential reason could be poaching. The use of the area by tiger in the eastern and northern part of the Reserve was lower than the rest of the Reserve. The habitat encroachment coupled with human induced pressure could be the reason for this. Removal of the encroachment will help to restore the last remaining few tigers in SWR. The improved protection has stabilized the tiger in later years but there are very few breeding females to contribute population growth significantly. The area is connected with the Reserve Forest of Pilibhit Forest Division and Kishanpur Wildlife Sanctuary (KWS) in UP, India and conserving the forest between the KWS and Pilibhit forest may help regaining the population in SWR.

In Nepal, a total of 121 adult tigers (100-194) were estimated in 2009, of this CNP had 91 adult tigers. In CNP, the number of tiger has increased to 125 (95-183) in 2010 thereby adding 34 adults more when whole Park including churia was surveyed by camera traps. Better estimation tools are available, providing realistic estimation of the number and density of tigers by using capture recapture analysis framework. The density estimation using camera trap is based on the estimation of boundary strip width which is widely viewed as weak link (Karanth et al. 2006, Soisalo and Cavalcanti 2006) and overestimation by using half the mean maximum distance (MMDM) moved by the individual tigers (Dice 1938, Stickel 1954). The use of Spatially Explicit Capture recapture (SECR) models to overcome the geographical closure issue in combination with habitat mask has been useful. To overcome key problems of individual heterogeneity in capture probabilities, movement of traps, presence of potential holes in the array and ad hoc estimation of sample area by adopting Bayesian approach of analysis of the hierarchical model using data augmentation is providing better results (Royle et al. 2009 a, b). The free software SPACECAP (Singh et al. 2010) provides reasonable estimates developed using the Bayesian approach though the software needs to be more users’ friendly and less time demanding in its operation.

The TAL’s potential as a long-term stronghold for tigers, as indicated by the sign of presence in 10 of the 14 TAL districts, emphasizes the need to re-establish breeding habitat and dispersal corridors across this region (Wikramanayake et al. 2004, Barlow et al. 2009).

The camera trap in 20 day session may not be sufficient for Churia as indicated by this study and further testing is needed to come up with higher maximum capture of tigers with sufficient recaptures allowing estimating tiger with higher confidence. Monitoring tigers to differentiate between the breeding and non-breeding sections of the population will increase power to detect change and improve inferences regarding population status and long-term viability. This demands minimum of two years of camera trap in the same area and recording the evidence of cubs accompanying females. Alternatively, traditional monitoring with pug mark and tracing should be carried on larger area (Barlow et al. 2009).

University and local volunteers along with staff members from government and conservation partners in a team were used to generate quality data in one hand, and first hand field experience to the volunteers working in the core PAs in the other hand. This has helped to build the trust amongst managers and volunteers have realized the challenges of protecting PA holding the endangered species as tiger, rhino and wild elephant. This in turn would help to get more support from community, and help to improve the quality research by the university volunteers in future.

The joint resolution between Nepal and India (June 30, 2010) has opened up new collaborating avenues for conservation of tiger. Coinciding the monitoring of tiger with the trans-boundary PAs to gather the information on transient tigers would further strengthen the information for both the countries. Future collaboration on genetic studies, focussing the transboundary PAs, corridors and tiger habitat for tiger meta-population studies, piloting use of the Monitoring System for Tigers-Intensive Patrolling and Ecological Status (MSTrIPES) in Nepal’s PAs and regular regional-local level trans-boundary meetings could be taken up for the benefit of the biodiversity conservation for both the countries.

The database prepared from this project was handed over to respective Parks and NTNC field offices. The hands on training to maintain and update is essential. Linking the MIS, ID based monitoring of rhino and MIST would provide information which would definitely help more access to researchers and managers in need.

At glance, the stronghold of tigers as a source population in Chitwan complex, potential to increase the tigers in Bardia and Suklaphanta complex and introduction/re-introduction of prey species in prey depleted area may certainly contribute to the global aim of doubling the tiger by 2022.