Using distance sampling with camera traps to estimate the density of group-living and solitary mountain ungulates
RAN J A N A PAL,TAP A J IT BHATT A CHAR Y A,QAMAR QURESHI STEPHEN T. BUCKLAND and SAMBANDAM S A THYAKUMAR
Abstract Throughout the Himalaya, mountain ungulates are threatened by hunting for meat and body parts, habitat loss, and competition with livestock. Accurate population estimates are important for conservation management but most of the available methods to estimate ungulate densities are difficult to implement in mountainous terrain. Here, we tested the efficacy of the recent extension of the point transect method, using camera traps for estimating density of two mountain ungulates: the group-living Himalayan blue sheep or bharal Pseudois nayaur and the solitary Himalayan musk deer Moschus leucogaster. We deployed camera traps in 2017–2018 for the bharal (summer: 21 loca- tions; winter: 25) in the trans-Himalayan region (3,000– 5,000 m) and in 2018–2019 for the musk deer (summer: 30 locations; winter: 28) in subalpine habitats (2,500– 3,500 m) in the Upper Bhagirathi basin, Uttarakhand, India. Using distance sampling with camera traps, we esti- mated the bharal population to be 0.51 ± SE 0.1 individuals/ km2 (CV = 0.31) in summer and 0.64 ± SE 0.2 individuals/ km2 (CV = 0.37) in winter. For musk deer, the estimated density was 0.4 ± SE 0.1 individuals/km2 (CV = 0.34)in summer and 0.1 ± SE 0.05 individuals/km2 (CV = 0.48)in winter. The high variability in these estimates is probably a result of the topography of the landscape and the biology of the species. We discuss the potential application of dis- tance sampling with camera traps to estimate the density of mountain ungulates in remote and rugged terrain, and the limitations of this method.
Keywords Bharal, camera trapping, density estimates, musk deer, point transect method, subalpine, trans- Himalaya, Upper Bhagirathi basin
Supplementary material for this article is available at
doi.org/10.1017/S003060532000071X
SAMBANDAM SATHYAKUMAR (Corresponding author, 2027-4706), RANJANA PAL (
orcid.org/0000-0003- orcid.org/0000-0002-6011-104X) and QAMAR
QURESHI Wildlife Institute of India, Chandrabani, Dehradun, Uttarakhand 248001, India. E-mail
ssk@wii.gov.in
TAPAJIT BHATTACHARYA (
orcid.org/0000-0002-1154-4033) Durgapur Government College, Durgapur, India
STEPHEN T. BUCKLAND (
orcid.org/0000-0002-9939-709X) The Centre for
Research into Ecological and Environmental Modelling, University of St Andrews, St Andrews, UK
Received 20 January 2020. Revision requested 29 May 2020. Accepted 22 July 2020. First published online 30 April 2021.
Introduction
ecosystems by influencing vegetation structure (McNaughton, 1979; Bagchi & Ritchie, 2010) and as primary prey for large predators (Bagchi&Mishra, 2006; Sathyakumar et al., 2013a). Population estimates are important for effective conservation management (Singh & Milner-Gulland, 2011; Suryawanshi et al., 2012). Methods to estimate animal abundance include distance sampling (Buckland et al., 2001), track count (Sulk- ava & Liukko, 2007), dung count (Laing et al., 2003), the abundance induced heterogeneity model (Royle & Nichols, 2003), repeated count (Royle, 2004) and the double observer method (Forsyth & Hickling, 1997; Suryawanshi et al., 2012; Suryawanshi et al., 2020). In mountains, however, rugged and steep terrain, inaccessibility and harshweather conditions make these techniques less effective (Singh&Milner-Gulland, 2011). As a consequence, several studies on mountain ungulates
U
have used an indirect index of abundance (e.g. Schaller et al., 1988; Sathyakumar, 1994; Bagchi&Mishra, 2006;McCarthy et al., 2008; Suryawanshi et al., 2010) as an alternative to ab- solute abundance. However, these estimates are less reliable and highly dependent on the assumption of constant de- tection probability throughout the survey period (Yoccoz et al., 2001). In addition, small population sizes, cryptic and elusive behaviour, and patchy distribution of Himalayan ungulates limit the number of observations that can be made for a given survey effort (Singh & Milner-Gulland, 2011). Forest-dwelling mountain ungulates may have activity peaks at night (Cavallini, 1992; Bhattacharya et al., 2012a) and are rarely detected during day-time surveys. Distance sampling is one of the most popular methods
for assessing the density of large herbivores in tropical forests (Buckland et al., 2001). However, meeting the un- derlying assumptions of this method in the mountains is difficult (Corlatti et al., 2015), which can lead to underesti- mation of population sizes. In the mountains, non-random locations of non-linear transects, inaccurate measurements of sighting distance and angle, and elusive behaviour of tar- get species violate the assumptions underlying conventional distance sampling (O’Neill, 2008; Singh & Milner-Gulland, 2011). Furthermore, the structure of mountainous terrain can hamper animal detectability, as animals hidden behind
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (
http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. 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
ngulates are an integral component of Himalayan mammalian fauna and play an essential role in shaping
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