Justification of Red List Category
This species is largely restricted to extensive tracts of primary evergreen forest within a region experiencing high rates of deforestation. Even though the species is widespread within its range, high hunting pressure is exacerbating the population decline caused by habitat loss. The species is thus suspected to undergo a large population reduction over the next three generations. Therefore, it is listed as Vulnerable.
The population size of this species has not been quantified. The species is widespread throughout its range, but occurs at low densities, even in suitable habitat (Poonswad et al. 2013).
In Peninsular Malaysia, Sungai Tekam Forestry Concession (Pahang State) population density was found to be 1.6 groups/km2 in primary forest and 2.3, 1.8, 1.2, 0.4 groups/km2 in 0-6 month, 1-2 year, 3-4, 5-6-year-old logged forest respectively (Johns 1987). In Kuala Lompat (Krau Wildlife Reserve) the population density was 2 individuals/km2 (Medway & Wells 1971). In Sarawak, Upper Baram and Batang Ai National Park had population densities of 0.27 individuals/km2 (Chin & Jantan 2001) and 0.96 individuals/km2 (Meredith 1995) respectively. In Sabah, Crocker Range Park and Tawau Hills Park had population densities of 0.94 individuals/km2 and 5.67 individuals/km2 respectively (Lakim & Biun 2005).
An analysis of deforestation between 2000 and 2012 estimated forest loss within the species's range at a rate equivalent to 35% over three generation lengths (42 years) (Tracewski et al. 2016). Being largely restricted to primary forests and intolerant of habitat conversion, the species is additionally threatened by hunting. Thus, its actual rate of population decline is likely greater than the estimate decline based on forest loss alone, possibly exceeding 35% over three generations. The rate of decline is therefore placed in the band 35-40% over three generations. Since this species has a long generation length, with three generations stretching over 42 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 35-40% over the next three generations.
Buceros rhinoceros is confined to the Sundaic lowlands of extreme south peninsular Thailand (where it is locally considered to be endangered, and the only suitable habitat is in extensive primary forest in the Hala Bala area [Trisurat et al. 2013]), Sabah, Sarawak and Peninsular Malaysia, Kalimantan, Sumatra and Java, Indonesia and Brunei (BirdLife International 2001). It is locally extinct in Singapore.It can be found in Peninsular Malaysia, Sabah and Sarawak but is absent from the smaller States such as Melaka, Penang and the Federal Territories. Its stronghold remains in large forest complexes and protected areas (Davison 1987; Davison 1995; Lim & Tan 2000; Wells 1999; Chong 1998; Chong 1993; Siti Hawa Yatim 1993; Siti Hawa Yatim et al. 1985; Ong et al. 2000; Choo and Teresa 2001; Norsham and Teresa 2001; Abdul Kadir Abu Hashim 2002; Wells 1999; Yeap & Perumal, in press; Wells 1990; Yong et al. 2011).
This species occurs in extensive areas of primary lowland and hill forest, extending into tall secondary forest and swamp forests, up to 1,400 m.When foraging, it crosses occasionally disturbed areas and plantations (Poonswad et al. 2013).
It mainly feeds on fruits, but also takes small animals like arthropods, lizards, tree-frogs and bird eggs (Kemp and Boesman 2018). It will eat a variety of fig species and often takes advantage of ripened trees (Zainal Zahari Zainuddin et al. 1998; Choo 2000). They are usually seen in pairs. Other smaller hornbill species, for example the Oriental Pied hornbill, Bushy-crested hornbill and Black hornbill avoid feeding at the same section or level of the fruiting fig tree as Rhinoceros hornbills. In some instances, they wait near the fruiting fig tree and approach when the Rhinoceros hornbills have left.
The Rhinoceros hornbill also forms large groups of up to 15 individuals (mostly young adults), which can be seen roaming the forest canopy together in Belum-Temengor Forest Complex (Yeap C.A. pers. obs.).
It breeds seasonally, with nests being placed in natural tree cavities in 9-15m height (Kemp and Boesman 2018). Breeding has been recorded in several Peninsular Malaysian States of Pahang, Selangor, Johor, and Perak (Kaur et al. 2015; Wells 1999). In Sabah, fledglings have been noted in Sungai Segama (Fogden 1965) and adult birds have also used artificial nests in Kinabatangan with a chick fledging successfully (HUTAN 2019). Nest tree species used by the hornbills include Koompassia malaccensis (Kaur et al. 2015). Breeding in Lanjak Entimau Wildlife Sanctuary, Sarawak has been recorded between November and March (L. Sir in litt. 2020).
Forest destruction in the Sundaic lowlands of Indonesia has been extensive as a result of commercial and illegal logging, as well as agricultural development. An analysis of forest loss from 2000 to 2012 estimated forest loss within the species's range at 43.8% across three generation lengths (Tracewski et al. 2016). Additionally, the species is known to be impacted by hunting. It is caught for food, trade and the use of body parts (namely its casque and tail feathers) in ceremonial dress (Kinnaird and O'Brien 2007, Kemp and Boesman 2018), especially on Borneo by the Iban and Orang Ulu communities (L. Sir in litt. 2020). The species may also be taken as ‘bycatch’ by hunters targeting Helmeted Hornbill Rhinoplax vigil (R. Wirth in litt. 2017). The rate of decline due to hunting is uncertain, however hunting for feathers and casques is likely to increase for commercial and cultural purposes via online platforms in Kalimantan, Indonesia (Y. Hadiprakarsa, pers. comm.)
Conservation Actions Underway
CITES Appendix II. Occurs in several protected areas, including Taman Negara National Park (Malaysia), Gunung Leuser, Bukit Barisan Selatan and Way Kambas National Parks and Berbak Game Reserve (Sumatra), Bukit Baka Bukit Raya National Park and Kapuas Hulu District (West Kalimantan, Indonesia) and Danum Valley Conservation Area (Borneo). The known North American ex situ population of this species is approximately 75 birds. Median life expectancy of this population is approximately 20 years, but individuals have lived well into their 30s. The age at first breeding in the population is five years old and birds have had offspring in their late 30s. The population has been growing over the last 20 years, driven by consistent reproduction at multiple institutions (AZA studbook, currently through November 12th 2018 and Species360, as of December 31st 2019; as reported by P. Schutz in litt. 2020).
c.90-100 cm. Very large black hornbill with black plumage, white thighs and vent and black band across the white tail; orange bill and prominent red horn-shaped casque with thick black line along the rear edge. Voice Gives a series of short, resonant rroh calls.
Text account compilers
Datta, A., Clark, J., Patil, I.
Aik, Y.C., Benstead, P., Gilroy, J., Hadiprakarsa, Y., Hermes, C., Kheng, S., Kinnaird, M., Martin, R., O'Brien, T., Schutz, P., Sir, L., Taylor, J., Westrip, J.R.S. & Wirth, R.
BirdLife International (2021) Species factsheet: Buceros rhinoceros. Downloaded from http://www.birdlife.org on 16/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/10/2021.