The tiger Panthera tigris is categorized as Endangered on the IUCN Red List (Goodrich et al., Reference Goodrich, Wibisono, Miquelle, Lynam, Sanderson and Chapman2022) and the snow leopard Panthera uncia as Vulnerable (McCarthy et al., Reference McCarthy, Mallon, Jackson, Zahler and McCarthy2017). Poaching, prey depletion, habitat loss and fragmentation, human–wildlife conflict and climate change are threatening both species (Seidensticker, Reference Seidensticker2010; Mir, Reference Mir2020; Rashid et al., Reference Rashid, Shi, Dong and Sultan2021). The global tiger population is estimated to be 2,608–3,905 (Nowel & Jackson, Reference Nowell and Jackson1996; Seidensticker et al., Reference Seidensticker, Christie, Jackson, Seidensticker, Christie and Jackson1999; Goodrich et al., Reference Goodrich, Wibisono, Miquelle, Lynam, Sanderson and Chapman2022) and that of the snow leopard is estimated to be 2,710–3,386 (McCarthy et al., Reference McCarthy, Mallon, Jackson, Zahler and McCarthy2017). Both species are umbrella species and play crucial roles in the functioning of the ecosystems they inhabit (Sunquist et al., Reference Sunquist, Karanth, Sunquist, Seidensticker, Christie and Jackson1999; Ripple et al., Reference Ripple, Estes, Beschta, Wilmers, Ritchie and Hebblewhite2014).

Habitat overlap of tigers and snow leopards in Bhutan has been previously reported based on evidence of tigers (pugmarks, livestock killed and camera-trap images) in known snow leopard habitat above 4,000 m altitude (Thinley et al., Reference Thinley, Lhendup and Dorji2015; Dendup et al., Reference Dendup, Dorji, Jamtsho, Wangchuk, Tshering and Dorji2021a). However, there has been no evidence of the two species sharing the same area, despite the burgeoning use of camera-trap surveys.

The 4,374 km² Jigme Dorji National Park is the second-largest protected area in Bhutan (Fig. 1). The Park contains elevations ranging from 1,200 to > 7,000 m, and experiences four distinct seasons. The Park has five distinct vegetation types: subtropical, warm temperate, cool temperate, subarctic/cold temperate forest and rhododendron scrub (Dendup et al., Reference Dendup, Wangdi, Jamtsho, Kuenzang, Gyeltshen and Tashi2021b). More than 5,000 people live in the Park, and they are permitted to harvest natural resources. However, to control indiscriminate resource collection the Park is delineated into four conservation management zones (Table 1), and people can only collect resources from the multiple-use zone (Dendup et al., Reference Dendup, Dorji, Jamtsho, Wangchuk, Tshering and Dorji2021a).

Fig. 1 Jigme Dorji National Park, Bhutan, indicating locations of the 56 camera-trap locations including those where only tigers Panthera tigris were photographed and those where both tigers and snow leopards Panthera uncia were photographed.

Table 1 The conservation management zones of Jigme Dorji National Park, Bhutan (Fig. 1).

The National Park has been identified as an important source site for tigers (Tempa et al., Reference Tempa, Hebblewhite, Goldberg, Norbu, Wangchuk and Xiao2019; Dendup et al., Reference Dendup, Lham, Wangchuk and Jamtsho2023). During the countrywide tiger survey conducted in 2014–2015, six individual tigers were identified in the National Park (Department of Forests and Park Services, 2015), and the 2021–2022 tiger survey also identified six individuals (Dendup, Reference Dendup2022; Dendup et al., Reference Dendup, Lham, Wangchuk and Jamtsho2023). The 2014–2016 countrywide snow leopard survey identified 31 individuals in the National Park, the highest number in a protected area in the country, followed by Wangchuck Centennial National Park with 17 individuals (Thinley et al., Reference Thinley, Lham, Wangchuk and Wangchuk2016). Here we report the habitat overlap and co-occurrence of tigers and snow leopards from a countrywide camera-trap survey that focused on tigers.

During October 2021–January 2022, camera traps (HyperFire 2, Reconyx, Holmen, USA) were installed in a grid of 56 5 × 5 km cells at altitudes of 1,200–4,300 m. Within each grid cell one camera-trap station comprising two camera traps was placed on human or animal trails along ridges or valley bottoms or at water holes, to maximize the probability of capturing tigers and their prey. The two camera traps were separated by at least 2 m, to avoid image distortion from each camera's flash. Cameras were mounted to a tree or a wooden pole 30–45 cm above the ground and 2.0–2.5 m away from trails, to enable images to capture tigers and other animals in full frame.

A total of 478 and 31 independent images of tigers and snow leopards, respectively, were captured over a total of 1,528 trap-nights (independent images of the same species are those captured > 30 minutes apart). Based on the unique stripe patterns of tigers and the unique spots and rosettes of snow leopards, six tiger individuals were identified in 21.4% (12 out of 56) of the camera-trap stations and two snow leopard individuals were identified in 5.4% (3 out of 56) of the camera-trap stations. All three stations that captured snow leopards also captured tigers, but with temporal differences in the capture events (Plate 1, Table 2). These three camera-trap stations were at 3,615–4,010 m altitude, in mixed conifer forest and alpine meadow, one in the core zone and two in the multiple-use zone.

Plate 1 Images of tigers Panthera tigris and snow leopards Panthera uncia captured at the same camera-trap locations in Jigme Dorji National Park, Bhutan (Fig. 1), at (a) 4,010 m; (b) 3,885 m; and (c) 3,615 m altitude (Table 2).

Table 2 Temporal differences in the occurrence of snow leopards Panthera uncia and tigers Panthera tigris photographed at three camera traps in Jigme Dorji National Park. For location IDs, see Plate 1.

During 1990–2010, forest cover in Bhutan increased by 1,147 km², a mean annual increase of 59 km², and there has also been an overall reduction in grassland, shrubland and barren areas. These changes have been attributed to the establishment of plantations, and changing climatic conditions (Gilani et al., Reference Gilani, Shrestha, Murthy, Phuntsho, Pradhan and Bajracharya2014). The upward movement of forests as a result of climate change could have increased the habitat for tigers and reduced snow leopard habitat, as has been reported previously for the common leopard Panthera pardus (Lovari et al., Reference Lovari, Minder, Ferretti, Mucci, Randi and Pellizzi2013). The habitat in which the tigers and snow leopards co-occur should be conserved both for their welfare and for that of other species, as the conservation of umbrella species is beneficial to other species within the same ecosystem (Alexander et al., Reference Alexander, Cusack, Chen, Shi and Riordan2016).

Photographic evidence of these two apex predators at the same camera traps in three separate locations is testimony of the effectiveness of conservation measures that have been implemented in the National Park. However, two of the three locations are in the multiple-use zone and therefore management is required to prevent habitat degradation in this zone or to explore the feasibility of incorporating the area into the transition zone, where traditional, sustainable use of natural resources is permitted only for a certain period (Jigme Dorji National Park, 2021). Our findings corroborate previous reports of the occurrence of tigers in presumed snow leopard habitat in Bhutan, and confirm habitat overlap and co-occurrence of the two species. These insights will be of value to researchers planning further work on these species.