Bhutan has designated more than half of its territory as protected, with biological corridors for maintaining habitat connectivity and facilitating wildlife movement between protected areas comprising c. 8% of the country (DoFPS, 2025). Although structural connectivity (i.e. topographical habitat continuity) is well documented, functional connectivity (realized animal movement) remains poorly validated with corridor-specific field evidence (Wildlife Conservation Division, 2010; Hilty et al., Reference Hilty, Worboys, Keeley, Woodley, Lausche and Locke2020). Documenting the use of these corridors by wide-ranging carnivores such as the tiger Panthera tigris is therefore essential for evaluating whether corridors function as intended.

The 419 km² Biological Corridor 7, which covers an altitudinal range of 797–4,370 m (Fig. 1) connects Wangchuck Centennial and Phrumsengla National Parks and Bumdeling Wildlife Sanctuary in north-eastern Bhutan (DFOM, 2023). Although tiger presence is confirmed in adjacent protected areas, national camera-trap surveys conducted in 2014–2015 and 2021–2022 did not record tigers within this corridor (DoFPS, 2015, 2023). Here, we present photographic evidence of tiger presence in Biological Corridor 7 and evaluate the seasonal ecological conditions associated with these detections.

Fig. 1

(a) Location of Biological Corridor 7 within Bhutan’s network of protected areas and corridors, which connects Wangchuck Centennial National Park, Phrumsengla National Park and Bumdeling Wildlife Sanctuary. (b) Locations of 31 paired camera-trap stations in a 3 × 3 km grid of 47 cells in Biological Corridor 7. A tiger Panthera tigris was recorded at Stations 29 and 30 in February 2025 (Plate 1).

Long description

Panel A: A map of Bhutan highlighting the protected areas and biological corridors. The map shows the location of Biological Corridor 7, which connects Wangchuck Centennial National Park (WCNP), Phrumsengla National Park (PNP), and Bumdeling Wildlife Sanctuary (BWS). The map includes international boundaries, protected areas, and biological corridors. Panel B: A detailed map of Biological Corridor 7 with a 3 by 3 kilometer grid. The grid contains 47 cells and marks the locations of 31 paired camera-trap stations. Stations 29 and 30 are highlighted as locations where a tiger was recorded in February 2025. The map also shows elevation variations within the corridor.

Plate 1

The left and right flanks of an adult male tiger Panthera tigris photographed in Biological Corridor 7 (Fig. 1) in February 2025. Markers 1–5 denote key features used for identification: (1) unforked mid-flank band, (2) single sweeping hip stripe, (3) evenly spaced tail rings, (4) thin parallel shoulder cluster, and (5) short lower flank bar.

We conducted a multi-species camera-trap survey in Biological Corridor 7 using a grid of 47 3 × 3 km cells (Fig. 1b) during January–July 2025. We deployed paired stations in 31 accessible cells across altitudes of 858–3,687 m for a total of 5,144 trap-nights. The design followed standard tiger and prey camera-trap survey methods and previous camera-trap research in biological corridors in Bhutan (Karanth & Nichols, Reference Karanth and Nichols2017; Letro et al., Reference Letro, Fischer, Duba and Tandin2022). Stations were along or at likely travel routes such as ridgelines, saddles and waterholes; inaccessible terrain was avoided (Karanth & Nichols, Reference Karanth and Nichols2017; Letro et al., Reference Letro, Fischer, Duba and Tandin2022). Each station was equipped with two motion-triggered infrared cameras (Panthera Xenon V7, Panthera, USA; Reconyx HF2 Pro, Reconyx, USA; or Cuddeback Ambush Professional, Cuddeback, USA) mounted 30–45 cm above ground and programmed to capture 1–3 photographs per trigger; paired cameras were spaced 3–4 m apart to minimize cross-triggering (Karanth & Nichols, Reference Karanth and Nichols2017). Independent events were defined using a 30-minute separation rule (Sollmann, Reference Sollmann2018). Tiger identity was determined by comparing stripe patterns with national catalogues, and verified by the Bhutan Tiger Centre (DoFPS, 2015, 2023). To examine seasonal conditions, we summarized independent prey events (barking deer Muntiacus muntjak, sambar Rusa unicolor and wild pig Sus scrofa) and human/cattle events by season (late winter: January–February; spring: March–May), standardized as events per 100 trap-nights (Hilbe, Reference Hilbe2011). Camera trapping continued until July, but the seasonal comparison was restricted to late winter and spring because these periods bracketed the tiger detections and had comparable survey effort. Prey event counts were modelled using negative binomial regression, with the logarithm of trap-nights included as an offset to account for variation in sampling effort, and with season, elevation scaled per 500 m, and a season × elevation interaction as predictors. Fitted values were used to estimate the expected number of prey events and the probability of recording at least one prey event per 100 trap-nights along the altitudinal gradient (Hilbe, Reference Hilbe2011).

Two independent events involving a single adult male tiger (Plate 1) were recorded in February 2025, with nine photographs across two stations. Seven photographs were captured on 9 February at Station 29 (Nyesa; 2,687 m; evergreen oak forest) and two photographs at Station 30 on 12 February (Shawa; 2,352 m; cool broadleaved forest). The stripe patterns did not match any individual in the national photo-identification database (DoFPS, 2015, 2023). The two stations were c. 3 km apart.

Prey detections were widespread throughout the study area. Effort-standardized event rates were higher in late winter than in spring for barking deer (10.60 vs 6.97), sambar (6.15 vs 3.63), and wild pig (5.58 vs 1.87). Negative binomial models indicated that sambar detections declined with elevation in spring, with an incidence rate ratio of 0.48 per 500 m increase in elevation (95% CI 0.30–0.75, P = 0.002). Across the elevational gradient, fitted models predicted higher expected prey events and a greater probability of recording at least one prey event per 100 trap-nights in late winter compared to spring (Fig. 2). At the two stations where the tiger was detected, human and cattle detections were less frequent in winter than in spring (humans 9.72 vs 21.74, cattle 1.39 vs 22.83 events per 100 trap-nights).

Fig. 2

Predicted prey camera-trap event rates from negative binomial models across elevation in Biological Corridor 7, Bhutan (Fig. 1). Sampling effort was accounted for by including trap-nights as an offset in the models. (a) Expected number of independent prey events per 100 trap-nights; (b) probability of detecting ≥ 1 event in 100 trap-nights. Solid and dashed lines show season-specific fitted means, and shaded ribbons show 95% CI.

These detections provide photographic confirmation of tiger presence in Biological Corridor 7 during late winter 2025. The absence of tiger records in the corridor in previous national surveys in 2014–2025 and 2021–2022 may be attributed to imperfect detection associated with a coarser sampling grid (5 × 5 km) and survey timing (October–December in Biological Corridor 7; DoFPS, 2015, 2023). Higher prey detections and lower human and cattle activity at Stations 29 and 30 in late winter suggest that tiger use of the corridor landscape may be linked to temporarily favourable conditions at mid-elevations. The 4-day interval between the detections at stations c. 3 km apart suggests local movement within the corridor, although this pattern could also reflect local ranging behaviour rather than movement between protected areas (Dhendup et al., Reference Dhendup, Sharma, Painter, Whiteley and Mills2023). These records do not demonstrate long-term occupancy or corridor-scale movement between protected areas. Biological Corridor 7 is a landscape used by both people and wildlife, and roads and settlements can narrow movement routes (DFOM, 2023). To facilitate wildlife movement through the corridor, narrow sections of corridors require targeted actions, such as improving road crossings, maintaining tree cover along movement routes, and constructing wildlife overpasses or underpasses where necessary (Thinley et al., Reference Thinley, Suberi and Dorji2025). We recommend repeated seasonal camera-trap surveys, complemented by non-invasive genetic sampling (Dhendup et al., Reference Dhendup, Sharma, Painter, Whiteley and Mills2023; Jeong, Reference Jeong, Hyun, Marchenkova, Matiukhina, Cho and Lee2024), to assess individual tiger turnover and gene flow through Biological Corridor 7.