Table of contentsIntroductionReasons for isolationConclusionIntroductionGlobal loss of biodiversity has increased exponentially in recent years and, according to BirdLife International (2018), approximately 1,469 bird species are threatened with extinction. Of these species, 222 are considered critically endangered. Biodiversity loss due to human-induced land-use change results in species loss, particularly in the tropics where species diversity and human pressures on natural environments are high (Dirzo and Raven, 2003 ). Some habitats lose more biodiversity than others, leading to an asymmetrical geographic distribution of threatened species. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Although some species have attracted the attention of conservationists (e.g., the Spoon-billed Sandpiper Calidris pygmeus and the Great Indian Bustard Ardeotis nigriceps; the Indian government has prepared guidelines for the recovery program of the GIB: see www.indiaenvironmentportal.org), others, for example, Jerdon's courser Rhinoptilus bitorquatus, Himalayan quail Ophrysia superciliosa and Manipur quail Perdicula manipurensis, in India, have received little attention despite the fact that the first two are critically endangered and the third is endangered (BirdLife International, 2013). Specific surveys (Jeganathan et al., 2002 for the Jerdon's Courser; Choudhury, 2006 and Baral et al., 2013 for the Himalayan Quail) have not improved 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, the species is critically endangered (BirdLife International, 2017). Figure 1 shows the historical and recent distribution of the WBH; previously the heron was restricted to undisturbed swamps, reed beds and marshes of eastern Nepal and Sikkim Terai, Bihar (north of the Ganges), duars of Bhutan to northern Assam, East Pakistan ( Bangladesh), Arakan and northern Burma (= Myanmar) (Ali and Ripley, 1987; and Walters 1976). Over the last two decades, it has been reported from Assam, Kaziranga National Park (Barua and Sharma 1999), Jamjing and Bordoloni of Dhemaji district (Choudhury 1990, 1992, 1994), Dibru National Park -Saikhowa (Choudhury 1994) and Pobitara wildlife reserve (Choudhury 1996a). In Arunachal Pradesh, it has been reported from the Namdapha Tiger Reserve, particularly from its fast-flowing rivers, namely Noa-Dihing, Namdapha and Debannalla (Choudhury 1996b, Maheswaran 2007, 2008). The Namdapha population is estimated at seven individuals (Mondal and Maheswaran, 2014). In northern Myanmar, WBH has been described as common along the Mali Kha River in Putao (Smythies 1953) and on the Irrawady River (Stanford & Ticehurst 1939). ). However, records in Myanmar as far south as Toungoo and Pegu suggest migration or other post-breeding dispersal (Hancock and Kushlan, 1984). King et al. (2001) during their surveys mentioned that the herons were seen in 1998 and 1999 along a large river near the village of Ziyardum (northwest of Putao) and the Nan Lam (Wasadam) river on a pebble bed. It is possible that these sightings are the first sightings of this species in Myanmar in many years. Figure 1: Map showing global distribution(recent and historical) of the WBH (Map downloaded from: BirdLife International, 2017) The heron population has remained low for many decades and probably since the early 19th century, as few sightings have been recorded anywhere in the range of the species (Ali & Ripley, 1987); although this may be due to limited bird watcher access to these isolated protected areas and security concerns. According to Kushlan (2007), 1% of the protected population's WBH threshold remains at 6 individuals and the global population at 250-1,000. BirdLife International (2017) estimated the WBH population at between 70 and 400 individuals. However, Price and Goodman (2015) estimated the global WBH population at fewer than 60 individuals. This number is highly prone to extinction if not adequately protected through immediate conservation actions. According to Szabo et al. (2012), the reasons for the extinction of bird species are numerous and cannot be attributed to a single cause, but extinction often occurs when new threats emerge outside of the species' evolutionary experience (Brook et al. 2008). The WBH species has not been observed 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 solely to eliminate the malaria mosquito, while the remaining wetlands disappeared as colonies expanded (Harris 1992) over the years. This may be one reason why herons disappeared along with the Sarus Crane (Grus antigone) from the southwestern Terai of Nepal, although the latter continue to be present in significant numbers in the south-central lowlands. It should be noted that heron access is limited. birders in remote areas of northeast India or across the border in northern Myanmar, with access to Namdapha only from the 1980s. The poor road network, rugged terrain and Logistical difficulties are 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 sighting of a pair of adult herons courting and nesting in the Namdapha Tiger Reserve, Arunachal Pradesh, India (Mondal and Maheswaran, 2014) was the only record from the country so far. We observed White-bellied Herons for 858.45 hours from 2013-2016 while feeding in the 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 heron feeding activities. During 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 at the search for prey; figure 3) and the number of fish captured were recorded. The herons were seen striking (Figure 4) the water 1,121 times, of which only 403 attempts were successful. As the results suggest, herons made fewer successful attempts (64%) compared to 36% unsuccessful attempts. Additionally, the species had a strike rate of 1.3 fish/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 that of Goliath herons (0.332).In Bhutan, the strike rate was 1.2 strikes per capture (RSPN, 2011). This implies that herons had easier access to fish in Bhutan than their counterparts in Namdapha, India. Reasons for isolation Based on recent observations, the WBH appears to have restricted its distribution and feeding habitats to fast-flowing rivers across its range, including in Myanmar and Bhutan. and India (Pradhan et al. 2007; Maheswaran, 2007), between 60 m and 1,300 m altitude (Choudhury, 2000). It is an established fact that over the last decade, habitat destruction and alteration has become commonplace across the Indian landscape as human population (e.g. Assam in the Brahmaputra floodplains has a human density of 400/km2 World Bank, 2014) has increased several times. The expansion of agriculture and the reclamation of natural wetlands for agriculture, particularly rice, has reduced the habitats of many native fauna, including waterbirds that directly depended 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 that this reason alone remained one of the main factors 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 evergreen 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 northeast India and the more temperate forests of Bhutan, because these ecosystems, unlike the plains, took longer to experience serious consequences. 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 for species such as the White-winged Duck (Cairina scutulata) and the WBH from the direct impact of land change. habitat, hunting and fishing, because these actions are prohibited inside protected areas. The heron's current preference to select isolated rivers in the region as its preferred habitat may have helped it remain unaffected by hunting pressure exerted by local people on other species outside protected areas. However, it becomes difficult to establish this claim because no data has ever been collected on inter- and intra-species interactions in India and elsewhere. When habitats surrounding major cities in northeast India began to feel pressure from human interventions after the 1990s, species like WBH may have remained in the more remote corners of the northeast's core forest areas of India, particularly in Arunachal Pradesh and Assam, but only within protected areas. , competition with other piscivorous species for space and food, in addition to disturbance by humans in the remaining wetlands (outside protected areas) of northeast India, may have driven the species further towards a habitat that remained its current permanent habitat. The thick forests with fast-flowing rivers of the Namdapha provide feeding (Figure 2) and breeding space for the WBH in India, this habitat perhaps rarely being preferred by other piscivorous birds (Maheswaran,2008). A possible explanation for why other fish-eating birds do not prefer Namdapha could be that open wetlands on the plains are remote and wandering birds searching for food find it increasingly difficult to locate habitat suitable other than fast-flowing rivers inland. thick patches of evergreen forest which, in turn, are unsuitable for other colonial piscivorous species found in the area (with the exception of cormorants). The WBH has a large body size, associated with a low fertility rate (RSPN, 2007) and probably shyness towards human presence. even in protected areas where human intervention is minimal. Collectively, these reasons may have been attributed to the species being driven further into isolation. Effects of isolation on the heron Maccarone et al. (2012) hypothesized that once a bird reaches a distant site, it faces less competition from other birds and is able to occupy itself with prey capture the entire 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 for the great cormorants Phalacrocorax carbo (Maheswaran, 2008). On a few occasions (n ​​= 4), we saw herons chasing cormorants when the latter approached very closely, especially when the herons were actively feeding. However, once we saw a cormorant chasing the heron who was holding his beak with fish. The cormorant tried to steal the fish from the heron but failed in his attempt. Additionally, herons were seen near black storks but both ignored each other. The reason why herons and cormorants showed aggressive behavior towards each other could be due to why both preferred fish of almost similar size, while the Black Stork always foraged on the river banks. main and was seen catching small fish (4-9 cm). In Bhutan, on two occasions when two foraging herons were approached closely by great cormorants, the herons flew away from the spot in search of another site (RSPN, 2011). It shows that great cormorants are one of the potential competitors of herons in India and Bhutan, more than any other fish-eating bird species. Among many groups of animals, aggregations occur particularly when foraging (Krause and Ruxton 2002), including 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 grounds using 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 gaining additional information about the location of available prey in a patch (Valone, 1989, Valone and Giraldeau, 1993), or perhaps learning from foraging tactics on novel prey types from other foragers (Krebs and Inman 1992, Beauchamp et al. 1997). Some species of wading birds have been shown elsewhere to simply act as focal or target members that attract others to feeding congregations.