Distance sampling with camera traps 669


FIG. 1 Study area in the trans-Himalayan region and subalpine region of the Upper Bhagirathi basin, with the locations of camera traps used for estimating densities of the bharal Pseudois nayaur, and Himalayan musk deer Moschus leucogaster, respectively. The inset map shows the location of the Bhagirathi basin in Uttarakhand State, Western Himalaya, India.


rocks or in valleys could remain undetected, irrespective of their distance from the observer. Camera traps are an efficient tool for detecting elusive


and rare species in remote habitats (Burton et al., 2015; Rovero & Zimmermann, 2016), and extending the point transect method to accommodate data from camera traps could help solve some of the issues related to the violation of the assumptions underlying classic distance sampling (Howe et al., 2017). Distance sampling with camera traps has recently been tested for estimating the populations of Maxwell’s duiker Philantomba maxwellii (Howe et al., 2017) and the western chimpanzee Pan troglodytes versus (Cappelle et al., 2019) in Côte d’Ivoire.However, the efficacy of this technique in mountainous terrain has yet to be tested. Mountain ungulates are threatened by hunting for meat


and body parts (Sathyakumar et al., 2013a,b), habitat loss (Namgail et al., 2007; Kittur et al., 2010) and competition with livestock (Mishra et al., 2004; Bhattacharya et al., 2012b) throughout theHimalaya. Here,we focused on theHimalayan


blue sheep or bharal Pseudois nayaur and the Himalayanmusk deer Moschus leucogaster, both of which are affected by anthropogenic impacts (Mishra et al., 2004; Bhattacharya & Sathyakumar, 2011). The bharal is a social species of the Caprinae subfamily. It is associated with alpine and steppe mountain pastures, and subalpine slopes devoid of tree cover (2,500–5,500 m; Prater, 1980;Sathyakumar & Bhatnagar, 2002). The species is categorized as Least Concern on the IUCN Red List and listed in Schedule I of the Indian Wildlife (Protection) Act, 1972. In contrast, the Himalayan musk deer is solitary and sedentary, remain- ing within a defined home range throughout the year. The musk deer, a primitive deer-like ruminant, is a member of the family Moschidae. In the Indian Himalayan region, the southern side of the Greater Himalaya, it is restricted to areas between 2,500mand the treeline (Green, 1985; Sathyakumar et al., 2013b). It is categorized as Endangered on the IUCN Red List (Timmins & Duckworth, 2015) and listed in the Indian Wildlife (Protection) Act, 1972, in Schedule I.


Oryx, 2021, 55(5), 668–676 © The Author(s), 2021. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S003060532000071X


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