Justification of Red List Category
This large hornbill qualifies as Vulnerable because it has a rapidly declining population as a result of the destruction of evergreen forest and hunting.
Density estimates in Thailand from 3 different sites have varied between 3.69 birds/km2 (Jornburom et al. 2010) in Huai Kha Khaeng Wildlife Sanctuary to 5.5 birds/km2 in Thung Yai Naresuan Wildlife Sacutaty (Jinamoy et al. 2013) and 8.06 birds/km2 in Thung Yai Naresuan West. Density estimates in Arunachal Pradesh, north-east India were 6.9 birds/km2 in Namdapha Tiger Reserve (Naniwadekar and Datta 2013) and 6.12 birds/km2 in Eaglenest Wildlife Sanctuary (Shukla et al. 2016). Based on these population estimates, coupled with an the extent of suitable habitat remaining within the occupied range of the species estimates that the global population is 12,000-15,000 individuals (R. Naniwadekar, A. Datta and P. Lo in litt. 2016). This is equivalent to 7,900-9,900 mature individuals, rounded here to 7,000-10,000 mature individuals.
Across much of its range, forest has been cleared at a rapid rate. In combination with intense hunting pressure (see Datta 2009, Naniwadekar et al. 2015a, Naniwadekar et al. 2016), these processes are inferred to be driving rapid population declines, placed here in the band of 30-49% decline over three generations (28.2 years; Bird et al. 2020).
Aceros nipalensis is currently known from Bhutan, north-east India, Myanmar, southern Yunnan and south-east Tibet, China, Thailand, Laos and Viet Nam. It has declined dramatically and is now very rare across much of its historical range. It is thought to be extinct in Nepal, and to be close to extinction in Vietnam (J. C. Eames in litt. 2007); it has also disappeared from many areas in Thailand.
The species remains widespread in Bhutan in the temperate and sub-tropical zones below 2,400m west to the Phuentsholing area, particularly the Mangde Chhu and Kuri Chhu valleys, and the species occurs at good densities in the Royal Manas, Phrumshengla, Jigme Singye Wangchuck National Parks (Spierenburg 2005), Phibsoo, Jomotshangkha, Bumdeling (southern parts) Wildlife Sanctuary, and Jigme Khesar Strict Nature Reserve. It is commonly also found in the districts of Zhemgang, Trongsa, Mongar, Lhuentse, Trashigang, Samdrup Jongkhar, Tsirang, Sarpang, and Chhukha in Bhutan (Penjore 2010, Dorji 2013, Sherub 2017).
In India the largest populations and greatest extent of suitable habitat are in Arunachal Pradesh, Sikkim, and the northern (Himalayan) part of North and West Bengal (Naniwadekar et al. 2016, R. Naniwadekar and A. Datta in litt. 2016). Relatively high densities (>6 birds per km2) have been recorded from both Namdapha Tiger Reserve and Eaglenest Wildlife Sanctuary (Naniwadekar and Datta 2013, Shukla et al. 2016). An earlier study in Arunachal Pradesh found significantly lower densities of hornbills outside Protected Areas primarily because of habitat degradation and hunting (Naniwadekar et al. 2015a). It is also present in eastern Nagaland with additional records from Cherrapunji in the Khasi Hills in Meghalaya, the Lushai Hills in Mizoram, near Jatinga in Assam and northern Manipur (Choudhury 2009, R. Naniwadekar et al. 2016), although only an estimated 1,280 km2 of suitable habitat remains in five of the north-eastern states (Naniwadekar et al. 2015a, Naniwadekar et al. 2016). Habitat-use probability of the the species was negatively associated with human population with populations having declined extensively across its range due to mature forest loss and hunting (BirdLife International 2001). The species was previously found in higher elevations (500-2,000 m) (Kemp 2001), explaining the positive association of the habitat-use probability with elevation. The species may now be primarily restricted to eastern portions of Nagaland due to much of the larger landscape being lower than its preferred elevation range. Moreover, in the Fakim-Saramati landscape, carcasses in villages have confirmed its presence here (A. Datta in litt. 2020). In Arunachal Pradesh, extent of suitable habitat is estimated to be around 2,500 km2 (Shukla et al. 2016), while in North Bengal, it may be around 500 km2 (A. Datta in litt. 2020). 75% of hornbill habitat in Arunachal Pradesh, India (where most of the species may be found) is also unprotected and is therefore at risk of habitat loss. The total extent of suitable habitat in India may be less than 5,000 km2 (A. Datta in litt. 2020).
There are records distributed throughout northwestern Myanmar, where it is perhaps locally common. The species is present in Kachin State, Chin State, and Sagaing through to Magwe Division in the south (Naing 2015). Recent records also show that the species may occur in restricted parts of southeastern Myanmar (eBird 2020). In Thailand, Rufous-necked Hornbills are now restricted to the Western Forest Complex, occurring in Huai Kha Khaeng, west Thailand Yai Naresuan Wildlife Sanctuary, Umphang Wildlife Sanctuary and Mae Wong National Park (Poonswad et al. 2013, Jinamoy et al. 2014). However, the species appears to have become extinct at Doi Inthanon and Doi Suthep-Pui National Park. The extent of suitable habitat in the country has been estimated at 1,315 km2, of which 1,288 km2 lies within protected areas (Trisurat et al. 2013). Suitable habitats additionally covers over 11% of world heritage sites within the region (Jinamoy et al. 2014). It is considered to still occur in the Nakai-Nam Theun National Biodiversity Reserve in Laos, though there is little recent information on the population in the country, which is also the case for the present situation in China. Previously, the species occurred at Xishuangbanna Nature Reserve in Yunnan, with numerous specimens obtained in the 1950-60s, but there have been no confirmed records for more than a decade (P. Lo, R. Naniwadekar and A. Datta in litt. 2016). The only recent confirmed records in China are from Medog, southern Tibet and Nangunhe Nature Reserve in southwest Yunnan in 2006, with further unconfirmed sightings in Tengchong on the western slope of Gaoligongshan (P. Lo, R. Naniwadekar and A. Datta in litt. 2016). A small population persists in Yen Bai province, Vietnam, and there is also an earlier confirmed record for Pu Mat National Park (Le Manh Hung et al. 2004).
It inhabits subtropical primary evergreen and deciduous forests generally between 300-2,400 m but has been recorded up to 2,900 m and locally down to 150 m. A significant frugivore, fruits of 21 plant species have been recorded in its diet in India, 17 in Thailand, and 35 in Bhutan (Chimchome et al. 1997, Naniwadekar et al. 2015b, Sherub 2017), however in Thailand, almost 22% of its diet was comprised of animal matter: crabs, snakes, cicadas and amphibians (Chimchome et al. 1997). In Bhutan, 13 animal species such as crabs, bird chicks, beetles, caterpillars, and even small mammals like squirrels and rats were recorded in the diet (UWICER 2017). The main food plants during the non-breeding season in Arunachal Pradesh were Canarium strictum, Prunus ceylanica, Ficus drupacea, Ficus altissima, Ficus geniculata, Machilus duthiei and Beilschmiedia assamica (Naniwadekar et al. 2015b). Unlike Great Hornbill Buceros bicornis, figs do not dominate the diet (Chimchome et al. 1997, Naniwadekar et al. 2015b). In Mongar district, Bhutan, species belonging to 20 families dominated by Lauracear and Anacardiaceae were recorded in their diets (UWICER 2017).
The nesting season in India and Bhutan begins in April, while in Thailand it commences in January; the duration of the nesting period is between 105-152 days (Poonswad et al. 2013). Tall, wide-girthed trees are required for breeding; nests have been recorded in Cleistocalyx nervosum in Thailand and in Terminalia myriocarpa, Altingia excelsa and Syzygium spp. in Arunachal Pradesh (Datta 2009, R. Naniwadekar in litt. 2016). Shorea robusta and Schima wallichi were also recorded as nest trees in Buxa TR (Pradhan et al. 2020). In Buxa TR, North Bengal, nest entry occurred between the end of March to the first week of May. The nesting cycle ranged from 99 to 121 days with chicks fledgling between mid-July to August (Pradhan et al. 2020).
The female seals herself inside the nest cavity with droppings and fruit pulp, emerging with the chick at the end of the nesting period. Clutch size is one to two eggs. In Huai Kha Khaeng in Thailand, the estimated nesting success was 68% and an adult pair raised, on average, 1.3 chicks per nest (n = 22 pairs) (Poonswad et al. 2013).
Generally the species is considered sedentary and territorial, but there is some evidence of seasonal movements in search of patchily distributed fruit resources (Tifong et al. 2007). The home range size of three individuals tracked by radio telemetry was approximately doubled during the non-breeding season when compared with the breeding season; around 12-16 km2 versus 6 km2 (Tifong et al. 2007). As the male is entirely responsible for feeding the female within the nest cavity during the breeding season, his foraging distance is greatly restricted.
Typically the species occurs in pairs or groups of 4-5 individuals, only occasionally being seen in larger groups of up to 15 (R. Naniwadekar and A. Datta in litt. 2016).
Its dependence on large trees for feeding and nesting makes it especially susceptible to deforestation and habitat degradation through logging, shifting cultivation and clearance for agriculture. Furthermore, viable populations require vast tracts of forest to survive, exacerbating its susceptibility to habitat fragmentation. These problems are compounded by widespread hunting and trapping for food, and trade in pets and casques. Hunting is the primary threat to the species in Arunachal Pradesh, India (Datta 2009, Naniwadekar et al. 2015a), where it is targeted primarily for meat (Naniwadekar et al. 2015a). As compared with the Great Hornbill and Wreathed Hornbill, Rufous-necked Hornbills often occurs in lower densities even in their optimal habitats (Dasgupta and Hilaluddin 2012, Naniwadekar and Datta 2013). In addition, their annual home ranges are small (c. 25 km2), they show strong affinity to hill forests and are not known to make wide-ranging movements (Tifong et al. 2007). This likely makes them more vulnerable to hunting.
Where Great Hornbill does not occur, the casque is used in ceremonial headgear, while the tail feathers are occasionally sought for cultural reasons, meat is consumed and some communities use the body fat for a purported medical value and even for polishing guns (Naniwadekar et al. 2016). In eastern Arunachal Pradesh the head of the species is frequently displayed in houses and was found in 61% of households sampled (Datta 2002).
Conservation Actions Underway
CITES Appendices I and II. The following protected areas support important populations: Royal Manas National Park, Phrumshengla National Park, Jigme Singye Wangchuck National Park, Phibsoo Wildlife Sanctuary, Jomotshangkha Wildlife Sanctuary, Jigme Khesar Strict Nature Reserve, Mangde Chhu and Kuri Chhu valleys, Bhutan; Eaglenest Wildlife Sanctuary, Namdapha Tiger Reserve, and Tale Wildlife Sanctuary in Arunachal Pradesh, India; Nakai-Nam Theun National Biodiversity Conservation Area, Laos, and Um Phang and Mae Wong National Parks and Huai Kha Khaeng and Thung Yai Wildlife Sanctuaries, Thailand. Field surveys have been conducted throughout much of the range of the species in India, with the exceptions of Manipur and Sikkim (Datta 2009, Naniwadekar et al. 2015a, R. Naniwadekar in litt. 2016). Protection and nest monitoring programmes have been established in North Bengal and western Arunachal Pradesh (Pradhan et al. 2020, R. Naniwadekar and A. Datta in litt. 2016). In Bhutan, the species is also listed as a Schedule I species in the Forest and Nature Conservation Act (1995) and as a 'totally protected species' under the Forest and Nature Conservation Rules and Regulations (DoFPS 2017).
Conservation Actions Proposed
Conduct further surveys to clarify its distribution and status in Myanmar, Laos and Viet Nam. Monitor trends in selected key populations. Initiate annual hornbill counts and continue movement and diet composition studies in Bhutan. Protect remaining extensive tracts of forest, extend existing protected areas where appropriate, and strictly control hunting in protected areas. Lobby for improved logging practices that leave patches of old growth or large trees. Design and implement hornbill conservation programmes aimed at reducing hunting levels.
117 cm. Large hornbill with distinctive rufous head and underparts. Males are black above with white-tipped outer primaries, white tail with black basal half, pale yellowish bill with row of vertical dark ridges on upper mandible and almost no casque, blue orbital skin and red gular skin. Female has black head, neck and underparts and slightly duller orbital skin. Juvenile is like male but bill smaller without dark ridges, tail feathers may be narrowly dark-tipped. Voice Loud barking kup or kok notes.
Text account compilers
Datta, A., Patil, I., Fernando, E.
Eames, J.C., Lo, P., Naniwadekar, R.N., Sherub, K., Kinley, Benstead, P., Mahood, S., Derhé, M., Hermes, C., Tobias, J., Peet, N., Davidson, P. & Bird, J.
BirdLife International (2022) Species factsheet: Aceros nipalensis. Downloaded from http://www.birdlife.org on 27/05/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 27/05/2022.