Introduction

The Terai Arc Landscape (TAL), at the foothills of the Himalayas in northern India, boasts approximately 14% of the global tiger population (Qureshi et al., 2023).  Amangarh Tiger Reserve (TR) in the western TAL provides a buffer to the dispersing  tiger individuals of Corbett TR and harbours a significant breeding population of tigers (Qureshi et al., 2023). Tigers rely on large home ranges, undisturbed habitats and abundant large wild ungulates to flourish (Karanth et al., 1999, Sunquist et al., 1981). The proposed Kandi road, connecting Kotdwar to Ramnagar towns of Uttarakhand at the inter-state border of Uttar Pradesh and Uttarakhand and running east to west along Corbett TR, cuts through the tiger connectivity between Corbett TR and Amangarh TR (DownToEarth 2024). This proposed road, may isolate the tiger population of Amangarh TR, increasing its vulnerability to local extinction caused by demographic and environmental stochasticity (Caughley 2002, Purvis et al., 2000). Further, the depletion of prey base abundance may threaten the tiger population and become a significant constraint on their recovery (Karanth & Stith, 1999, Wikramanayake et al., 2002, Harihar et al., 2009). Understanding population parameters of prey species such as density, group size and social organisation, which are inherently linked to ecosystem effectiveness, is crucial for conservation-related decisions (Jathanna et al., 2003, Witmers 2005, Skalski et al., 2010). Various techniques have been used to assess such population parameters for the prey base (Dinerstein 1980, Karanth et al.,1992) and distance sampling is a robust statistical method to estimate the density and abundance of the prey base. This method also accounts for missed animals during the surveys by estimating detection probability using effective strip width (Buckland et al., 2015). We applied this method to generate baseline information on wild prey base for long-term conservation of tigers in Amangarh TR.

This study focuses on ungulates, a critical food source for large carnivores. They constitute a significant portion of the prey consumed by carnivore populations across numerous protected areas in India (Schaller, 1967; Johnsingh, 1983; Karanth & Sunquist, 1995; Biswas & Sankar, 2002). It is also important to understand the ecosystem services that ungulates are providing to the habitats upon which they survive. Therefore, monitoring wild prey base becomes an essential part of the conservation and management of large carnivores.

Study Area

Amangarh TR (95 km²) is situated in the Himalayan foothills in the Bijnor district of Uttar Pradesh and forms the southern boundary of Corbett Tiger Reserve. The forested area of the TR (80.6 km²) was sampled (Fig. 1). Before the formation of Uttarakhand state in 2000, Amangarh was buffer area of the Corbett TR. Amangarh TR has a tiger density of 9.34 (±1.96 SE) /100 km^-2 (Qureshi et al., 2023). Tigers use Corbett and Amangarh as a continuous habitat and move towards Terai West Forest Division and eventually to Ramnagar Forest Division (Bisht et al., 2019; Qureshi et al., 2023). The broad forest type is deciduous with sal and teak dominated forest and a generally flat terrain (altitude varies from 240 m to 270 m above sea level). Amangarh TR consist of sal , sal-mixed, plantation, scrubland and riverine vegetation types across its 9 beats. Amangarh TR is also one of the strongholds of Van Gujjar (a forest-dwelling nomadic tribe) population. They live inside the forest in traditional huts (also known as Deras) alongside their livestock and rely on the forest for grazing and lopping trees to sustain their herd. Hussain et al. (2012) reported 73 Van Gujjar families (557 individuals) inhabiting the area with 1690 units of livestock.

Figure 1: The location of Amangarh Tiger Reserve in Uttar Pradesh,
various land use land cover classses (acquired from living atlas of ESRI) and distribution of transects.

Methodology

Line transect based distance sampling (Eberhardt, 1978; Burnham et al., 1980; Buckland et al., 1993, 2001) was used to estimate the abundance of ungulates. In distance sampling, estimates are based on observed distances of animals from a line or point to model species detectability and estimate absolute density (Buckland et al. 1993). With a well-described theoretical framework and comprehensive software, distance sampling has become a widely used technique across a broad spectrum of species and is often used for large-scale monitoring of species that can be visually detected in reasonable numbers (Kumar 2000; Focardi et al. 2005). A total of 12 transects were marked in all the 9 beats of Amangarh TR. The transect length varied from 1-2 km. Transects were distributed randomly representing different vegetation types with respect to animal distribution in the study area (Fig. 1). Each transect was walked 6 times as temporal replicates. Transects were walked twice a day- early morning (06:00-07:00 hrs) and evening (16:00-17:00 hrs), when ungulates remain most active. Data on species sighted, the number of individuals and group composition were recorded. The angular distance was recorded using a handheld compass and a range finder. The start and end points of all the transects were also recorded using Global Positioning System (GPS) eTrex 30 for marking locations of transects on a map. We used Distance 7.5 release 1 software (Thomas et al., 2010) to estimate density and associated variance. Bins width was adjusted according to the collected data and best-fit model was selected based on the lowest AIC (Akaike Information Criterion) value (Fig. 2).