Tiger reappearance in Bhutan’s Bumdeling Wildlife Sanctuary: a case for maintaining effective corridors and metapopulations

Abstract

The tiger Panthera tigris is globally ‘Endangered’ (Goodrich et al., 2015). The Himalayan Kingdom of Bhutan is an important stronghold (Tempa et al., 2019) for this ecologically and economically important apex predator (Estes et al., 2011; Thinley et al., 2018). Here, we report the reappearance of the tiger in Bumdeling Wildlife Sanctuary (BWS) in north-eastern Bhutan (Fig. 1a), after a likely absence of 12 years. Bumdeling Wildlife Sanctuary is bordered by China in the north and India in the east, and covers 1520 km2 across the districts of Trashiyangtse, Mongar and Lhuentse (Fig. 1a). Altitudes range from 1500 to 6450 m above sea level and the sanctuary contains 745, 42 and 334 species of plants, mammals and birds, respectively (BWS, 2013). Other large predators present in the sanctuary include the snow leopard P. uncia, common leopard P. pardus and dhole Cuon alpinus. They subsist on a diverse ungulate community comprising sambar Rusa unicolor, muntjac Muntiacus muntjac, blue sheep Pseudois nayaur, musk deer Moschus chrysogaster, serow Capricornis thar and goral Naemorhedus goral. There are approximately 800 people who are resident in BWS, predominantly living as subsistence agro-pastoralists (BWS, 2013). Evidence of tiger presence in BWS was initially based on an anecdotal sighting at Thiling village in Sherimuhung Geog in 2001 (subdistrict; Fig. 1b); a claim of 12 yaks predated by tiger between 2003 and 2004 at Rongmateng village in Khoma Geog (Fig. 1b); and sanctuary personnel documenting tiger pugmarks in 2004 at Dongla within Yangtse Geog (Fig. 1b). However, camera trapping in BWS after 2004, including a comprehensive National Tiger Survey (NTS) from 2014 to 2015, failed to capture any tiger images (Thinley et al., 2015). This absence of sightings puzzled local tiger biologists, given the historic presence of tigers in the area, adequate prey availability, minimal hunting and no tiger poaching. Dissatisfied by the poor camera trapping results, sanctuary staff intensified field surveys in 2016 and a tiger pugmark was detected above Rigsumgeonpa monastery in Bumdeling Geog (Fig. 1b). Concurrently, three horses and eight sheep were depredated at Tsango village in Khoma Geog, allegedly by a tiger. Subsequent camera trapping at these livestock predation sites captured 22 tiger images (Fig. 2a,c), confirming at least one individual’s presence within BWS. Opportunistic camera trapping exercises in 2017 yielded nine tiger images (Fig. 2d) near Pangliwog village in Bumdeling Geog, and five images in Sherimuhung Geog. A 2018–2019 study of wildlife in water catchments in BWS and its environs yielded further three tiger images (Fig. 2e) above Gangkardung village in Bumdeling Geog within BWS, and 11 images (Fig. 2b) outside BWS and above Bayling and Bimkhar villages in Yangtse Geog. Analysis of all 50 images revealed a single male tiger, which did not match any of the 68 individual tigers identified in the NTS. This animal could have been an irregular transient not detected in pre-2016 camera trapping, but now resident at BWS. It is unlikely to have ranged from China or India given the functional extinction of the tiger in China (Qin et al., 2015), and no existing tiger records in India adjacent to BWS, due to rampant poaching (Passang Dorji, Forest Ranger, Trashiyangtse Range, Pers. Comm.). The male tiger in BWS is more likely to have originated from populations (Tempa et al., 2019) in either Wangchuck Centennial National Park via Corridor 8, or from Phrumsengla National Park via Corridor 7 (Fig. 1a). The reappearance of the tiger in BWS showcases the effective functionality of Bhutan’s biological corridors. Ensuring this and other tigers’ future survival in BWS entails regular anti-poaching patrols and camera trap monitoring; compensation or insurance programs to offset tiger-related livestock depredation; and designation of a corridor connecting BWS to Sakteng Wildlife Sanctuary (SWS; Fig. 1a). SWS is also linked to Jhomotshangkha Wildlife Sanctuary (JWS; Fig. 1a); both sanctuaries recorded tigers during the NTS, potentially harboring important metapopulations. Radio-collaring of tigers in BWS, SWS and JWS will substantiate ecological research on these metapopulations and confirm the functionality of associated corridors.