Rufous-necked Hornbill in Bhutan

The rufous-necked hornbill (Aceros nipalensis) is a large forest hornbill of the foothills and middle hills of the eastern Himalaya. The male is unmistakable, with rufous head, neck and underparts, a black back and wings, a broad white wing band visible in flight, and a long pale-yellow bill set against blue facial skin. The species is assessed as Vulnerable on the IUCN Red List, with a global population estimated at around 1,500 to 7,000 mature individuals and a continuing decline driven by logging, hunting and the loss of mature nest trees.^[1][2]

In Bhutan the species occurs in mature broadleaf and mixed forest of the southern foothills and middle hills, especially in Royal Manas National Park, Jigme Singye Wangchuck National Park, Phibsoo (Phipsoo) Wildlife Sanctuary, Phrumshengla National Park and the lower elevations of Bumdeling Wildlife Sanctuary. Population trends in Bhutan have not been precisely quantified, but published surveys indicate that the country supports one of the most secure remaining populations in the species' range, particularly in the central and south-central protected area network.^[3][4]

This article covers the species' identification, its Bhutanese distribution, habitat preferences, breeding biology, threats and the legal and institutional protections currently in force.

Identification

The rufous-necked hornbill is a large bird, with adults around 117 centimetres long. The male has rich rufous head, neck, breast and belly, glossy black back and wings, a broad white tip to the tail and a yellowish bill ridged with dark casque markings. The female is smaller, with the rufous areas replaced by black, but retains the same wing pattern and bill shape. In flight the heavy whoosh of the wings carries through valley forests for hundreds of metres and is often the first cue to its presence.^[2]

Distribution and habitat in Bhutan

Published surveys record the species across the southern and central forest belt. Tshering, Penjor and colleagues have documented its presence in the dzongkhags of Samtse, Chhukha, Sarpang, Zhemgang, Mongar, Trashigang and Samdrup Jongkhar, with reliable detections along the Punatshangchhu and in the Manas catchment. The species is reported between roughly 150 and 2,200 metres above sea level, although it concentrates in mature evergreen broadleaf forest between about 600 and 1,800 metres.^[3][5]

Royal Manas National Park, sharing a contiguous block of subtropical broadleaf forest with India's Manas Tiger Reserve, is regarded as the country's single most important hornbill stronghold. Phibsoo Wildlife Sanctuary, immediately west of Manas, holds the only sal-dominated forest in Bhutan and is similarly important. Jigme Singye Wangchuck National Park covers the central forest core and connects these two areas through biological corridors.^[3][6]

Habitat and ecology

The species depends on tall, structurally intact broadleaf forest with large emergent trees suitable for nesting cavities. Like other Asian hornbills, the female seals herself into a tree-hole nest with a wall of mud and droppings, leaving only a narrow slit through which the male feeds her and the chicks throughout incubation and the early nestling period. The nest tree is therefore a critical resource, and the loss of mature emergents to selective logging or natural die-back is a recognised limiting factor.^[2][7]

The diet is mainly fruit, particularly figs, with seasonal additions of small vertebrates, large invertebrates and nestling birds. As a long-distance fruit disperser the species plays a documented ecological role in the regeneration of mature broadleaf forest, a role amplified in the relatively intact forests of the southern Bhutanese belt.^[1][2]

Threats

The Bhutan-focused work by Tshering and colleagues identifies four principal threats: timber extraction, road construction, the clearance of forest for power transmission lines and the gradual die-back of nesting trees. Hunting pressure, while a serious problem elsewhere in the species' range, is reported as comparatively low within Bhutan's protected areas because of the country's strong forest law enforcement, although casual disturbance and accidental disturbance during forestry operations remain documented concerns.^[3][5]

Habitat modelling work using MaxEnt by researchers including Penjor and Choki has projected a contraction of suitable habitat under climate-change scenarios, with shifts towards higher elevations and more easterly latitudes by mid-century. The same modelling identifies the central-southern forest corridor as the area most likely to retain suitability under all projected scenarios.^[8]

Legal protection and monitoring

Within Bhutan the species is listed in Schedule I (totally protected) under the Forest and Nature Conservation Act and its associated rules. It is also listed in Appendix II of the Convention on International Trade in Endangered Species (CITES). Monitoring within protected areas is carried out by the Department of Forests and Park Services, with technical support from the Royal Society for Protection of Nature (RSPN) and the Bhutan Bird Conservation Society. The species is one of the flagship birds for conservation messaging in the southern foothill parks.^[3][9]

References

1. Rufous-necked Hornbill Aceros nipalensis species factsheet — BirdLife DataZone
2. Rufous-necked hornbill — Wikipedia
3. Tshering, Penjor and others, “Distribution and Threats of Rufous-necked Hornbill (Aceros nipalensis) in Bhutan”
4. Rufous-necked hornbill — IUCN Hornbill Specialist Group
5. Distribution and Threats of Rufous-Necked Hornbill in Bhutan — International Journal of Scientific Research
6. Royal Manas National Park — UNESCO World Heritage Centre Tentative List
7. Rufous-necked hornbill species page — Thai National Parks
8. Penjor and others, “Understanding the impact of climate change on the habitat of the rufous-necked hornbill in Bhutan” — Ornithology Research, Springer Nature
9. Aceros nipalensis — IUCN Red List