Distance sampling with camera traps 675
imprecise estimates of the target species’ availability for detection can cause erroneous estimates. Care should thus be taken in selecting the appropriate time period of animal activity and availability for detection (Howe et al., 2017). Distance sampling with camera traps has paved the way
for a new analytical approach to estimate the abundance of both group-living and solitary mountain ungulates in rug- ged and inaccessible terrains of the Himalaya. It can to some extent overcome the logistic constraints associated with rugged terrain and harsh weather that affect other methods such as point counts and transects sampling. These traditional methods are difficult to implement effec- tively in a high-altitude, rugged and remote landscape be- cause they require cover of most vantage points in a single day or within a defined, short period of time (Singh & Milner-Gulland, 2011). In addition, the low number of de- tections often limits the conventional analytical process. Indirect observations such as dung counts can be useful but require estimation of the decay rate, which is often dif- ficult to obtain (Buckland, 2001; Kuehl et al., 2007). Distance sampling with camera traps can work for longer periods in the field and may help to overcome the challenges presented by low numbers of detections and observer bias (Cappelle et al., 2019). An important advantage of camera traps over conventional distance sampling is that they are better suited to monitor solitary, elusive and nocturnal species such as the Himalayan musk deer. Camera traps have been extensively used to survey the snow leopard Panthera uncia. A slight modification in the sampling design (modified camera placement) could help gain information on its main prey species, including the bharal, the ibex Capra sibirica, the argali Ovis ammon and the musk deer. Despite these advantages, there are limitations to the use of
camera traps, including the high cost of the cameras and the extensive time required to process photographs and videos. Substantial numbers of camera traps would be required to improve the precision of density estimates derived from distance sampling with camera traps (Cappelle et al., 2019). Despite the high initial cost, we believe this approach could help improve abundance estimations for both group living and solitarymountain ungulates in rough, mountainous ter- rain where conventional techniques cannot be implemented.
Acknowledgements This work is part of a project initiated un- der the National Mission for Sustaining the Himalayan Ecosystem (NMSHE) Programme funded by the Department of Science and Technology, Government of India (grant no.: DST/SPLICE/CCP/ NMSHE/TF-2/WII/2014[G]). The Miriam Rothschild Travel Bursary Programme provided funding for a 4-week internship for R. Pal with S. T. Buckland at St Andrews University, UK.We thank the Director and Dean of theWildlife Institute of India for their guidance and support; D.V.S. Khati, Principal Chief Conservator of Forests and Chief Wildlife Warden, Uttarakhand, for granting research permission; Sandeep Kumar, Divisional Forest Officer and former Deputy Director, Gangotri National Park, and Shrawan Kumar for their sup- port and cooperation; and L. Corlatti for reviewing the manuscript.
Author contributions Conception of study: SS, RP, TB, QQ; data collection: RP; data analysis: RP, STB, TB; writing: all authors; revi- sions: QQ, STB, SS.
Conflicts of interest None.
Ethical standards This work was carried out with permission from Uttarakhand Forest Department (Letter no. 836/5-6) and abided by the Oryx guidelines on ethical standards.
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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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