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As biodiversity is distributed unevenly around the globe, so are threats to species and vulnerability to extinction. A practical conservation approach is to prioritize the focus of conservation efforts. Approaches that spatially prioritize biodiversity conservation such as hotspots (Myers et al., Reference Myers, Mittermeier, Mittermeier, da Fonseca and Kent2000), endemic bird areas (Stattersfield et al., Reference Stattersfield, Crosby, Long and Wege1998), crisis ecoregions (Hoekstra et al., Reference Hoekstra, Boucher, Ricketts and Roberts2005), global 200 ecoregion (Olson & Dinerstein, Reference Olson and Dinerstein1998) and the Last of the Wild (Sanderson et al., Reference Sanderson, Jaiteh, Levy, Redford, Wannebo and Woolmer2002) are used by international conservation organizations to prioritize and allocate conservation efforts. These approaches have been successful in influencing donors and funding agencies to invest in these regions (Brooks et al., Reference Brooks, Mittermeier, da Fonseca, Gerlach, Hoffmann and Lamoreux2006; Grenyer et al., Reference Grenyer, Orme, Jackson, Thomas, Davies and Davies2006; Wilson et al., Reference Wilson, McBride, Bode and Possingham2006). Although each approach uses different criteria, Bhutan, as part of the biodiverse Eastern Himalayan region, has been recognized as a conservation priority area by all these five approaches (Olson & Dinerstein, Reference Olson and Dinerstein1998; Stattersfield et al., Reference Stattersfield, Crosby, Long and Wege1998; Myers et al. Reference Myers, Mittermeier, Mittermeier, da Fonseca and Kent2000; Hoekstra et al., Reference Hoekstra, Boucher, Ricketts and Roberts2005.

Although Bhutan is recognized as part of most biodiversity conservation priority networks, few efforts have been made to document the country's biodiversity. Most of the existing information, particularly for mammals, is based on historical samples, anecdotal sources and sign surveys carried out in a few protected areas. These methods have detected common and large mammals but missed rare and elusive species such as most wild felids. Breakthroughs in camera-trapping technology have made it possible to study many of these rare and elusive species and the method has become commonplace for the inventory of many terrestrial species (Srbek-Araijo & Garcia, Reference Srbek-Araujo and Chiarello2005; Azlang & Lading, Reference Azlan and Lading2006; Tobler et al., Reference Tobler, Carrillo-Percastegui, Leite Pitman, Mares and Powell2008), including felids and other carnivores (O'Connell et al., Reference O'Connell, Nichols and Karanth2010).

In Bhutan the only previous published camera-trap study was of the tiger Panthera tigris and common leopard Panthera pardus in the central part of the country (Wang & Macdonald, Reference Wang and Macdonald2009). Here we report the results of a camera-trap survey, with a focus on wild felids, in the lower foothills of Bhutan, in Royal Manas National Park.

A grid of 2.5 × 2.5 km cells was overlain on our study (Fig. 1) area using ArcGIS v. 9.3 (ESRI, Redlands, USA). Clusters of 30 cells were systematically sampled close to Manas base camp, taking into consideration logistic and security constraints. Within a cell we set up cameras in locations based on the presence of felid sign (mostly of tiger) such as pug-marks, scrape marks, scent marks and scats. To maximize the probability of capturing wild felids we placed cameras along trails and river basins and beds that had the highest density of signs within a grid cell. At each station two cameras (passive infra-red Reconyx HC500 Hyperfire; RECONYX, Inc., Wisconsin, USA) were set 6–7 m apart at a height of 45 cm, to photograph both flanks of any passing animal (Karanth, Reference Karanth1995). Camera sensitivity was set very high, to record all species. The first camera trap was established on 7 November 2010 and the last on 17 November 2010, and we used data from 17 November 2010 to 12 February 2011. Camera traps were monitored twice per month, whenever possible, to replace batteries and renew camera memory cards.

Fig. 1 Bhutan, showing the protected area network, including designated biological corridors and the study area in Royal Manas National Park (RMNP). BWS, Bumdeling Wildlife Sanctuary; JDNP, Jigme Dorji National Park; JSWNP, Jigme Singye Wangchuck National Park; KWS, Khaling Wildlife Sanctuary; PWS, Phibsoo Wildlife Sanctuary; SWS, Sakteng Wildlife Sanctuary; TNP, Thrumshingla National Park; TSR, Torsa Strict Nature Reserve; WCP, Wangchuck Centennial Park.

Images were classified into independent events based on several criteria. If the same animal was captured multiple times within 1 minute then it was classified as a single event. If two or more animals were captured in a single image, all animals were considered independent events. For tigers, common and clouded leopards Neofelis nebulosa we identified individuals based on stripe patterns on flanks, head, tail and limbs. For all wild felids we calculated photographic rates as number of independent events divided by total trap nights (Carbone et al., Reference Carbone, Christie, Conforti, Coulson, Franklin and Ginsberg2001; Rovero & Marshall, Reference Rovero and Marshall2009).

From a total of 2,036 trap nights we confirmed the presence of six species of wild felids (Table 1, Supplementary Plate S1) and 28 other species of terrestrial mammals (Supplementary Table S1, Plate S2) in our study area of 74 km². Of the six species, the common leopard was captured by almost all camera stations and had the highest photographic capture rate (Table 1). Of the smaller felids, leopard cat was the most common. Marbled cat Pardofelis marmorata and Asiatic golden cat Pardofelis temminckii were the least common. Although, our study was not designed for estimating abundance, we detected 10 individual tigers, 20 individual common leopards and seven individual clouded leopards.

Table 1 The six species of wild felid photographed by camera trap (Supplementary Plate S1) in Royal Manas National Park (Fig. 1), with their Red List category (IUCN, 2012), number of photographic events, photographic rates (number of independent events divided by total trap nights) and number of days required for one event, ordered by photographic rate.

* LC, Least Concern; NT, Near Threatened; VU, Vulnerable; EN, Endangered

Our study indicates that Royal Manas National Park is a hotspot of wild felid diversity. Comparable wild felid diversity has been documented in the nearby Jeypore-Dehing rainforest in the north-eastern Indian state of Assam (CEPF, 2010) and from the Yungas biosphere of Argentina (Di Bitteti et al., Reference Di Bitteti, Albanesi, Foguet, Cuyckens and Brown2011). Both of these studies were conducted in much larger areas (500 km² in India, > 1,000 km² in Argentina). We consider that the six species of felid detected in the Park is a minimum as we also expect that at least two other species, the jungle cat Felis chaus and fishing cat Prionailurus viverrinus, inhabit the area because they are known to be in Manas National Park, India, which boarders our study area (Roy, Reference Roy1992). A camera-trap survey in Manas National Park in India from November 2010 to February 2011 reported five species of felids, including the jungle cat (Borah et al., Reference Borah, Sharma, Das, Rabha, Kakati and Basumatri2012). Three months after our survey a jungle cat was captured just west of our study area within the Royal Manas National Park. We may not have detected the fishing cat because because we did not place camera trap near their typical riverine habitat.

Conservation organizations and institutions have to allocate their resources to areas where conservation impact can be maximized in terms of number of species conserved per unit cost (Wilson et al., Reference Wilson, McBride, Bode and Possingham2006). Our results show that Royal Manas National Park is a diverse hotspot for wild felids. If the objective of conservation is to save the greatest number of species from extinction, then focusing conservation efforts and resources in areas such as Manas will be most effective in meeting conservation objectives.