Justification of Red List Category
This species is restricted to large tracts of undisturbed forest within a region experiencing high rates of deforestation. High hunting pressure is likely exacerbating the population decline caused by habitat loss. The species is suspected to undergo a large population reduction over the next three generations. Therefore, it is listed as Vulnerable.
Consistent population densities within protected areas in west and northeast India and Thailand of between 1.3 and 4 individuals per km2 indicate that the population within these sites, given the approximate habitat that lies within a suitable elevation range, can be estimated on a precautionary basis at 23,000 - 71,000 individuals. This is placed in the band 20 - 49,999 individuals, roughly equating to 13,000 - 27,000 mature individuals. Outside protected areas, even if adjacent, population densities can be considerably lower, often well below 1 individual per km2 (Gale and Thongaree 2006, Mudappa and Raman 2009, Naniwadekar et al. 2015).
An analysis of deforestation between 2000 and 2012 estimated forest loss within the species's range at 26.1% over three generation lengths (55.2 years) (Tracewski et al. 2016). The species is generally intolerant of forest disturbance and additionally severely threatened by hunting. Thus, its actual rate of population decline is likely greater than the estimate decline based on forest loss alone. The rate of decline is tentatively placed in the band 30-49% over three generations. Since this species has a long generation length, with three generations stretching over 55 years, there is insufficient evidence to calculate the magnitude of reduction over the past three generations. Assuming the recent rate of decline remains constant, the species is projected to decline by 30-49% over the next three generations.
Buceros bicornis has a wide distribution, occurring in China (rare resident in west and south-west Yunnan and south-east Tibet), India (locally fairly common, but declining), Nepal (local and uncommon, largely in protected areas), Bhutan (fairly common), Bangladesh (vagrant), Myanmar (scarce to locally common resident throughout), Thailand (widespread, generally scarce but locally common), Laos (formerly common; currently widespread but scarce and a major decline has occurred), Vietnam (rare and declining resident), Cambodia (rare), peninsular Malaysia (uncommon to more or less common) and on Sumatra, Indonesia (now rare).
The bulk of the population is found in India, where it is restricted to the Himalayan foothills, hill forests in northeast India and, disjunctly, the wet evergreen forests of west India. In the north and northeast there continue to be records from Uttarakhand, Uttar Pradesh, West Bengal, Assam, Meghalaya, Arunachal Pradesh, Nagaland and Mizoram, while in the wet western forests it occurs in Maharashtra, Goa, Karantaka, Kerala and Tamil Nadu (R. Naniwadekar and A. Datta in litt. 2016). Most are found within protected areas, principally National Parks (Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), Wildlife Sanctuaries (Birand and Pawar 2004, Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), Tiger Reserves (Birand and Pawar 2004, Mudappa and Raman 2009, Rahmani 2012, R. Naniwadekar and A. Datta in litt. 2016), and Reserved Forests (R. Naniwadekar and A. Datta in litt. 2016). The species was not recorded in unprotected forests in a state-wide survey of Arunachal Pradesh, although a significant population does occur in Reserved Forests (Naniwadekar et al. 2015). Outside of protected areas, the species is in severe decline or even locally extinct (Naniwadekar et al. 2015, J. Praveen in litt. 2018). An interview-based survey across Arunachal Pradesh indicated that the species had been lost from five out of 16 sites in recent decades, including from two protected areas (Naniwadekar et al. 2015).
In Nepal, Great Hornbill is present in Royal Chitwan and Bardia National Parks, though at relatively low density.It is patchily common in Bhutan, with the Mangde Chhu valley, the Royal Manas and the southern part of the Jigme Singye Wangchuck National Park the stronghold of the species in the country and populations apparently stable (Spierenburg 2005).
The Chinese population is restricted to the southwest of the country, with scattered reports in south Yunnan along the international borders (P. Lo in litt. 2016) and it is common at lower elevations in Yingjiang, from where there are breeding records (P. Lo in litt. 2016).
In Myanmar it is poorly known, though there are recent records from Sagaing and Kachin states in the north and from Nat Ma Tung National Park in the west of the country (King et al. 2001, eBird 2017).
An assessment of all hornbills across Thailand found Great Hornbill to be one of the more habitat tolerant species, yet the area of occurrence for the species is only approximately one third of the area of suitable habitat present in 1992 (Trisurat et al. 2013). The species has been extirpated from the Mae-Ping-Omkoi protected area complex in north Thailand (Pattanavibool et al. 2004). Away from the north it occurs in most protected-area complexes in the country and is present in particularly high densities in Khao Yai National Park (R. Naniwadekar and A. Datta in litt. 2016).
In Laos the species still present in Nakai-Nam Theun National Biodiversity Conservation Area, but appears to have declined considerably since being historically described as common.
It is now highly localised in Vietnam, with most recent records from Cat Tien National Park and Deo Nui San in the south, but also from Phong Nha-Ke Bang National Park in central Vietnam (eBird 2017).
The Cambodian population is concentrated in southern Mondulkiri in the southeast and the Cardamom and Elephant Mountains in the southwest, with small numbers also present where patches of evergreen forest persist in the north of the country (Goes 2013).
In Peninsular Malaysia it remains widespread and is present in several protected areas and is common on the island of Langkawi (R. Naniwadekar and A. Datta in litt. 2016, eBird 2017). However, the loss of lowland forest throughout the country is considered to have greatly reduced the area of suitable habitat present. On Sumatra it is now highly localised and very infrequently seen following extensive destruction of lowland forests (K. D. Bishop in litt. 2012).
This species frequents wet evergreen and mixed deciduous forests, ranging out into open deciduous areas to visit fruit trees and ascending slopes to at least 1,560 m in south India (Mudappa and Raman 2009) and up to 2,000 m in Thailand (Poonswad et al. 2013). The abundance of this species tends to be correlated with the density of large trees, required for nesting, and it is therefore most common in unlogged forest (Datta 1998). Known nest trees include Tetrameles nudiflora, Dipterocarpus gracilis, Dipterocarpus turbinata, Cleistocalyx nervosum, Shorea faguetiana, Hopea odorata, Neobalanocarpys heimii, Palaquiuum ellipticum, Mangifera indica, Bombax ceiba, Mesua ferrea and Syzygium gardneri (R. Naniwadekar and A. Datta in litt. 2016). It has also been reported to nest in the non-native tree Grevillea robusta (R. Naniwadekar and A. Datta in litt. 2016). In general, habitat-use seems to be negatively associated with human population (A. Datta and R. Naniwadekar in litt. 2018).
Figs comprise a major part of the diet (Kannan and James 1999, Datta and Rawat 2003, Naniwadekar et al. 2015b) but the species also takes eggs, amphibians, reptiles, insects, mammals and small birds (Kemp and Boesman 2017). The breeding season begins in March in northeast India, and between December and January in other parts of the range; throughout, the nesting period lasts around four months (Poonswad et al. 2013). As the female is incarcerated and dependent on the male during this time, home range size is considerable smaller (0.7 - 7 km2 [Poonswad and Tsuji 1994, R. Naniwadekar and A. Datta in litt. 2016]) than during the non-breeding period when it has been recorded as 138 km2 in Thailand (Keartumsom et al. 2011) and c. 50 km2 in northeast India (R. Naniwadekar and A. Datta in litt. 2016).
Forest loss likely has detrimental impacts on this species throughout its range, particularly as it shows a preference for forest areas with large trees that may be targeted by loggers. A deforestation analysis from 2000-2012 estimated the rate of forest loss within the species's range at 26% over three generations (Tracewski et al. 2016). Forests are lost to illegal logging and land conversion mainly for housing and agricultural developments, from small-scale agriculture to large-scale plantations. Because of its exceptionally large home range, the species requires extensive tracts of undisturbed forest and is unable to persist in areas where lowland forest has been reduced to small fragments (Chang et al. 2013). Proximity to human population is strongly avoided (A. Datta and R. Naniwadekar in litt. 2018). In the species's stronghold in north-eastern India, only 5% of the landscape offers suitable habitat (Naniwadekar et al. 2016).
Hunting poses a substantial threat to the species. Because of its predictable behaviour when regularly visiting the same feeding sites, it is easily targeted by local hunters. A survey in north-eastern India found that the species is mainly hunted for food as well as for its casque and tail feathers, which are used as adornments by local communities (R. Naniwadekar and A. Datta in litt. 2016, A. Datta and R. Naniwadekar in litt. 2018). Moreover, the species is highly prized for its fat, which is used for a variety of purposes, ranging from medical treatments to gun polish (A. Datta and R. Naniwadekar in litt. 2018). The species is also captured for the pet trade (Eames 2008), with chicks reported as being collected in south India and Thailand (R. Naniwadekar and A. Datta in litt. 2016), and may also be taken as 'bycatch' by hunters targeting Helmeted Hornbill Rhinoplax vigil (R. Wirth in litt. 2017).
Conservation Actions Underway
CITES Appendix I. The species is captively bred in zoos (Jensen 2008). It occurs in several protected areas across its range. The ecology of the species has been studied since 1981 as part of long-running research at Khao Yai National Park in Thailand (Poonswad et al. 1987, Poonswad 1995, Poonswad et al. 1998, 2005). Active management of nesting cavities has been used to augment breeding success in the wild (Poonswad et al. 2005). Hornbill Nest Adoption Programs have been implemented in Budo Sungai-Padi National Park in southern Thailand since 1994 (Pasuwan et al. 2011) and in forests adjoining Pakke Tiger Reserve in Arunachal Pradesh, northeast India since 2011 (Rane and Datta 2015). Urban donors are encouraged to 'adopt' wild hornbill nests and the funds raised are used to pay for nest guardians to monitor and protect the nest sites. An additional nest monitoring and protection program is underway in Kerala with the Kadar community and the forest department (Bachan et al. 2011). Artificial nest boxes have been installed with some success at sites in Thailand (Pasuwan et al. 2011) and southern India (James et al. 2011).
Conservation Actions Proposed
Monitor populations across its range to determine the magnitude of declines and rates of range contraction. Campaign for the protection of remaining extensive tracts of lowland forest throughout its range. Develop a programme to reduce hunting of the species through raising awareness of the status of the species within communities that target the species. Develop the existing captive breeding population to support future reintroduction and supplementation efforts.
c.100 cm. A very large black hornbill with a black band across the white tail; neck and throat yellow; white bands on the wing-coverts; male has a flat casque with a black rim which is double-pointed at the front, the female has a smaller casque without the black rim; casque only developed in mature individuals (>5 years). Voice Gives a series of short rroh calls.
Text account compilers
Benstead, P., Khwaja, N., Martin, R., Hermes, C., Taylor, J., Westrip, J., Gilroy, J.
Praveen, J., Lo, P., Naniwadekar, R.N., Datta, A., Wirth, R., Bishop, K.D.
BirdLife International (2019) Species factsheet: Buceros bicornis. Downloaded from http://www.birdlife.org on 22/11/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/11/2019.