IndexIntroductionReasons for isolationConclusionIntroductionAcross the world, biodiversity loss has increased exponentially in recent years and according to BirdLife International (2018), approximately 1469 bird species are threatened with extinction. Of these, 222 species are considered critically endangered. Biodiversity loss due to human-caused land use changes results in species loss, especially in the tropics, where both species diversity and human pressures on natural environments are high (Dirzo and Raven, 2003) . More biodiversity is lost in some habitats than others, leading to a distorted geographic distribution of threatened species. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay While some species have received attention from conservationists (e.g. the spoon-billed sandpiper Calidris pygmeus and the Indian bustard Ardeotis nigriceps; the Indian government has prepared guidelines for the GIB recovery program: see www. indiaenvironmentportal.org), others for example, Jerdon's Courser Rhinoptilus bitorquatus, Himalayan Quail Ophrysia superciliosa and Manipur Bush Quail Perdicula manipurensis, have received little attention in India despite the first two being critically endangered and the third endangered of extinction (BirdLife International, 2013). Dedicated investigations (Jeganathan et al., 2002 for Jerdon's Courser; Choudhury, 2006 and Baral et al., 2013 for Himalayan Quail) have not helped improve our understanding of their status. The White-bellied Heron Ardea insignis (WBH) has received little attention until recently, with the preparation of a single species conservation action plan (Price and Goodman, 2015). According to the IUCN Red List it is critically endangered (BirdLife International, 2017). Figure 1 shows the historical and recent distribution of WBH; previously the heron was limited to the undisturbed swamps, reeds and marshes of eastern Nepal and Sikkim Terai, Bihar (north of the Ganges River), the duars of Bhutan up to northern Assam, eastern Pakistan (Bangladesh) , Arakan, and Northern Burma (= Myanmar) ( Ali and Ripley, 1987; and Walters 1976). In the last two decades it has been reported in Assam, from Kaziranga National Park (Barua and Sharma 1999), Jamjing and Bordoloni of Dhemaji district (Choudhury 1990, 1992, 1994), Dibru-Saikhowa National Park (Choudhury 1994) and Pobitara Wildlife Sanctuary (Choudhury 1996a). In Arunachal Pradesh, it has been reported in the Namdapha Tiger Reserve, particularly in its fast-flowing rivers, namely Noa-Dihing, Namdapha and Debannalla (Choudhury 1996b, Maheswaran 2007, 2008). The Namdapha population is estimated to consist of seven individuals (Mondal and Maheswaran, 2014). In northern Myanmar, WBH has been described as common along the Mali Kha River at Putao (Smythies 1953) and on the Irrawady River (Stanford & Ticehurst 1939). ). However, records in Myanmar as far south-east as Toungoo and Pegu suggest migration or other post-breeding dispersal (Hancock and Kushlan, 1984). King et al. (2001) in the course of their investigations mentioned that herons were sighted in 1998 and 1999 along a large river near the village of Ziyardum (northwest of Putao) and on the Nan Lam (Wasadam) River on a bed of pebbles. It is possible that these sightings were the first sightings of this species in Myanmar for many years. Figure 1: Map showing the global distribution (recent and historical) of WBH (map downloaded from: BirdLife International, 2017) The heron population has remained lowfor many decades and probably since the beginning of the 19th century, as few sightings have been recorded throughout the species' range (Ali & Ripley, 1987); although this may have been a result of ornithologists' limited access to these remote protected areas and security challenges. According to Kushlan (2007), the 1% conservative population's WBH threshold remains at 6 individuals and the global population at 250-1000. BirdLife International (2017) estimated the WBH population at 70–400 individuals. However, Price and Goodman (2015) estimated the global WBH population to be fewer than 60 individuals. This number is highly prone to extinction if not adequately protected with immediate conservation actions. According to Szabo et al. (2012), the reasons for the extinction of bird species are many and cannot be traced back to a single cause, but extinction often occurs when new threats emerge from outside the evolutionary experience of the species (Brook et al . 2008). The WBH has not been recorded in Nepal since the 19th century and is considered “regionally extinct” (Inskipp et al., 2016). In the early 1960s, many national and international agencies helped the Nepalese eradicate malaria. Many wetlands were drained just to eliminate the malaria mosquito, while the remaining wetlands were lost as settlement progressed (Harris 1992) over the years. This may be one reason why herons have disappeared along with the Sarus crane (Grus antigone) from the Terai of southwestern Nepal, although the latter continue to occur in significant numbers in the south-central plains. It should be noted that there has been only limited ornithologist access to remote areas of northeast India or across the border into northern Myanmar, with access to Namdapha only since the 1980s. Poor road networks, rugged terrain and logistical difficulties have been the reasons attributed to poor surveys targeting avifauna and other wildlife in the region (Srinivasan et al. 2010). Very little is known about the breeding habits of this species, with recent information coming from Bhutan (RSPN, 2007). The observation of a pair of adult herons courting and nesting within the Namdapha Tiger Reserve, Arunachal Pradesh, India (Mondal and Maheswaran, 2014) was the only record in the country to date. We observed white-bellied herons for 858.45 hours starting from 2013. -2016 while foraging in rivers such as Noa-Dihing and Namdapha within Namdapha. The continuous focal sampling method (Altman, 1974; Martin and Bateson, 2007) was used to record various foraging activities of herons. During the foraging observations, the start and end time of each foraging period, the number of foraging attempts (defined as the number of times the heron hits the water with its beak in search of prey; Figure 3) and the number of fish caught. The herons were seen hitting the water (Figure 4) 1121 times, of which only 403 attempts were successful. As the results suggest, the herons made fewer successful attempts (64%) versus 36% unsuccessful ones. Additionally, the species had a strike rate of 1.3 strikes/hour and a catch rate of 0.5 fish/hour. In Bhutan, heron catches were infrequent and almost similar to those recorded in India, i.e. 11 fish in 78 hours (0.45 fish/hour) and also similar to those of Goliath herons (0.332). In Bhutan, the hit rate was 1.2 hits per capture (RSPN, 2011). This implies that herons had easier access to fisheries in Bhutan compared to their counterparts in Namdapha, India. Reasons for Isolation From recent observations, the WBH appears to have limited its distribution and foraging habitatsto fast-flowing rivers throughout its range, including Myanmar, Bhutan and India (Pradhan et al. 2007; Maheswaran, 2007), ranging from 60 m to 1300 m altitude (Choudhury, 2000). It is an established fact that over the last decade or so, habitat destruction and alteration have become rampant in the Indian landscape as human population (for example, Assam in the Brahmaputra floodplains has a human density of 400/km2 ; World Bank, 2014) has increased many times. The expansion of agriculture and the reclamation of natural wetlands for agriculture, particularly rice, have reduced the habitats of much native fauna, including waterfowl that depended directly on these habitats. Other studies (Seitre and Seitre 1992; Milberg and Tyrberg 1993; Butchart et al. 2006; Blackburn et al. 2004) reaffirm that habitat loss due to agricultural expansion and overexploitation has affected species worldwide and this single reason remained a major cause of extinction and sometimes acted simultaneously (Didham et al. 2005). In Assam and Arunachal Pradesh, tropical moist forest cover, which is the most diverse and found at lower altitudes, declined by 1.38% per year between 1994 and 2002 compared to tropical and subtropical evergreen forests ( Kushwaha and Hazarika, 2004). . With the loss of wetlands in the plains, herons may have been forced to remain in the tropical and subtropical evergreen forests of northeastern India and the more temperate forests of Bhutan as these ecosystems, unlike the plains, took longer to witness severe habitat changes such as road/dam construction and jhum cultivation. The declaration of some important habitats as protected areas, including national parks and sanctuaries, has provided refuge to species such as the white-winged duck (Cairina scutulata) and the WBH from the direct impacts of habitat alteration, hunting and fishing, as these actions are prohibited within protected areas. The heron's preference in current times to choose isolated rivers in the region as its preferred habitat may have helped it to remain unaffected by the hunting pressure exerted by the local population on other species outside of protected areas. However, it becomes difficult to establish the above statement as no data on inter- and intra-species interactions have ever been collected from India and elsewhere. When habitats surrounding major cities and towns in northeast India began to feel pressure from human interventions after the 1990s, species like WBH may have remained in the remotest corners of major forest areas in northeast India, especially in Arunachal Pradesh and Assam, but only within protected areas. , competition with other fish-eating species for space and food, as well as human disturbance in the remaining wetlands (outside of protected areas) in northeastern India, may have pushed the species further towards a habitat that remained their current permanent habitat. Dense forests with fast-flowing Namdapha rivers provide food (Figure 2) and breeding space for WBH in India, perhaps this habitat rarely preferred by other piscivorous birds (Maheswaran, 2008). One possible explanation for why other piscivorous birds do not prefer Namdapha may be that open wetlands in the lowlands are remote and wandering birds in search of food find it increasingly difficult to locate any suitable habitat other than the fast-flowing rivers inland. dense patches of evergreen forest which in turn are not suitable for other colonial species that feed on fish present in the region (except cormorants). The WBH has large dimensionsbodies, together with a low fertility rate (RSPN, 2007) and probable shyness towards human presence even within protected areas where human interventions are minimal. Collectively these reasons may have been attributed to the species being pushed further into isolation. Effects of isolation on the heron Maccarone et al. (2012) hypothesized that once a bird reaches a remote site, it faces less competition from other birds and is able to participate in prey capture all the time. In the case of the Namdapha WBH, the success rate is lower despite the fact that the reserve is remote and has no other foraging flocks, except the great cormorants Phalacrocorax carbo (Maheswaran, 2008). On some occasions (n=4) we saw the herons chasing the cormorants whenever the latter got very close to the herons, especially while the herons were actively searching for food. However, we once saw a cormorant chasing the heron that had the beak of a fish. The cormorant tried to steal the fish from the heron but failed in his attempt. Also, herons were seen near the black storks but both ignored each other. The reason why herons and cormorants showed aggressive behavior towards each other could be because they both preferred fish of almost similar size, while the Black Stork always foraged on the banks of the main river and saw small fish caught (4-9cm). In Bhutan, on two occasions, while two foraging herons were closely approached by great cormorants, the herons flew away from the site in search of another site (RSPN, 2011). This shows that great cormorants are one of the potential competitors of herons in India and Bhutan than any other species of fish-eating birds. Among many groups of animals, aggregations occur primarily during foraging (Krause and Ruxton 2002), even among wading birds (e.g., Erwin 1983b, Kersten et al. 1991, Master et al. 1993). Several hypotheses have been proposed to explain how individuals benefit from foraging in mixed-species aggregations. There is evidence that mixed-species aggregations of wading birds often form in areas of high prey density (Kushlan, 1976b, Erwin et al. 1985, Smith 1995). Whereas other studies have shown that wading birds locate their feeding sites by taking advantage of the presence of other foragers; this is often called “local improvement” (Krebs 1974, Kushlan 1976, Caldwell 1981, Erwin 1983b). Similarly, foraging success may also be improved by obtaining additional information about the location of prey availability within an area (Valone 1989, Valone and Giraldeau 1993), or they might learn foraging tactics from new types of prey. other collectors (Krebs and Inman, 1992, Beauchamp et al. 1997). It has been shown elsewhere that some species of wading birds simply act as focal or target members that attract others to mixed-species congregations in search of food (Kushlan 1977, Smith 1995, Strong et al. 1997). Dark-plumaged WBHs do not attract other species like their white-plumaged counterparts. Similarly, by foraging in groups, some species benefit significantly because they expend less energy foraging alone (Hafner et al. 1982, Master et al. 1993). The WBH appears to be a predominantly solitary eater, although it has been recorded in small groups of four to five individuals; with a single record of six individuals in a swamp lined with elephant grass (Choudhury 2000; Mondal and Maheswaran, 2014). Additionally, it has been observed with the gray heron (Ardea cinerea) and others.