Tiger Monitoring in Bhutan Using Non-invasive Genetic Tools

Large carnivores are one of the most threatened group of animals in the world. They suffer from prey depletion, persecution by humans, and habitat loss and fragmentation which are extensively driven by anthropogenic activities. One such species is the tiger Panthera tigris. Tigers are found in thirteen countries in Asia and are protected across the range; however, tiger numbers have declined as an after effect of habitat loss, prey depletion and poaching. Human-induced changes have reduced the tiger\u27s historical range to about 7% in which a little more than 3900 tigers are found. Most of these individuals currently exist in small and highly structured populations. Obtaining reliable estimates of population size and density and a solid understanding of the connectivity between populations are critical to understanding crucial aspects of effective tiger conservation. Bhutan, with a vast expanse of contiguous pristine forest cover, abundant prey, and active conservation policies, form a very critical part of tiger conservation in South Asia. However, due to limited funds, monitoring is erratic. Camera traps are a sought-after tool for monitoring tiger population and density in Bhutan, but costs have been a limiting factor. Therefore, we evaluated non-invasive genetic sampling (NGS) as an effective alternative to camera trapping for monitoring tigers in Bhutan. We carried out systematic camera trap and scat surveys in Royal Manas National Park in Southern Bhutan in 2018 and compared density, variability, and costs between the two methods. The densities were estimated under a spatially-explicit capture-recapture framework, and camera trap and NGS produced a density of 2.38 tigers/100 km2(95% CI 1.11-4.02) and 3.6 tigers/100km2(95% CI 1.06-12.23) respectively. Density and other parameters were estimated more precisely using camera traps, but the field and equipment cost was high as compared to single-session genetic sampling. When controlled for sampling effort, NGS performed better. There is also no information regarding population connectivity and gene flow in tigers within Bhutan. We genotyped 24 individuals using thirteen microsatellite loci and found that Bhutanese tigers overall have a high genetic variation (He=0.75). Individual-based and multivariate analyses indicated three genetic clusters within the sampled individuals; however, the overall genetic differentiation was low (FST=0.44). Our results suggest that Bhutanese tigers can be a source of genetic variation in the region and could play a crucial role in the long-term persistence of the species. We strongly recommend a transboundary and landscape-level conservation approach using common genetic data sets to understand tiger dispersal, threats, and other factors influencing dispersal events