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 (BirdLife International 2001).
An assessment based on population densities from sites in Arunachal Pradesh, north-east India and western Thailand coupled with an estimate of 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, these processes are suspected to have driven rapid population declines.
Aceros nipalensis is currently known from Bhutan, north-east India, Myanmar, southern Yunnan and south-east Tibet, China, Thailand, Laos and Vietnam. 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 tropical zones west to the Phuentsholing area, particularly the Mangde Chhu and Kuri Chhu valleys, and the species occurs at good densities in the Royal Manas, Thrumsing La, and Jigme Singye Wangchuck National Parks (Spierenburg 2005).
In India the largest populations and greatest extent of suitable habitat are in Arunachal Pradesh and the northern (Himalayan) part of West Bengal (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, R. Naniwadekar and A. Datta in litt. 2016). 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 and A. Datta in litt. 2016), although only an estimated 1,280 km2 of suitable habitat remains in these states (Naniwadekar et al. 2015a, R. Naniwadekar in litt. 2016).
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). It is not clear if any remain in the southeast of the country.
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). 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).
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 600-2,000 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, and 17 in Thailand (Chimchome et al. 1997, Naniwadekar et al. 2015b), however in the latter almost 22% of its diet comprised animal matter: crabs, snakes, cicadas and amphibians (Chimchome et al. 1997). 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).
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). 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). Where Great Hornbill does not occur, the casque is used in ceremonial headgear, while the tail feathers are occasionally sought for cultural reasons and some communities use the body fat for a purported medical value (R. Naniwadekar and A. Datta in litt. 2016). In eastern Arunachal Pradesh the head of the species is frequently displayed in houses, being 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, Thrumshing La National Park, Jigme Singye Wangchuck National Park, 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). The Hornbill Nest Adoption Program has been established in India focusing on protecting the nests of Rufous-necked Hornbill outside protected areas in central and western Arunachal Pradesh (R. Naniwadekar and A Datta in litt. 2016).
Conservation Actions Proposed
Conduct further surveys to clarify its distribution and status in Myanmar, Laos and Vietnam. Monitor trends in selected key populations. 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
Davidson, P., Benstead, P., Derhé, M., Bird, J., Hermes, C., Mahood, S., Peet, N., Tobias, J.
Naniwadekar, R.N., Datta, A., Lo, P., Eames, J.C.
BirdLife International (2020) Species factsheet: Aceros nipalensis. Downloaded from http://www.birdlife.org on 13/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 13/08/2020.