Wreathed Hornbill

The wreathed hornbill is a tropical bird belonging to the Old World hornbill family Bucerotidae. Sometimes called the bar-pouched wreathed hornbill, it is distinguished by the blue-black band on its inflatable throat sac and by the long, curved bill that develops characteristic ridges or “wreaths” on the casque as the bird matures. Males display striking contrasts of black plumage, white facial areas and a vivid yellow throat, whereas females are uniformly darker with blue throat skin. Occupying evergreen forests from Northeast India and Bhutan across mainland Southeast Asia to the Greater Sunda Islands, the species plays a vital ecological role as a long-distance seed disperser. It is currently listed as Vulnerable owing to widespread habitat loss and hunting pressures.

Taxonomy and Evolutionary Relationships

The species was first formally described in 1812 by the English naturalist George Shaw, who assigned it to the genus Buceros. Subsequent taxonomic revisions placed it in Rhytidoceros, Rhyticeros, and later Aceros. Contemporary ornithological consensus recognises the wreathed hornbill as a monotypic member of Rhyticeros, a genus defined by relatively low, ridged casques.
Mitochondrial DNA analyses comparing multiple hornbill species show a close phylogenetic relationship between Rhyticeros undulatus, members of Aceros, and the Visayan hornbill (Penelopides panini). These findings support the view that casque structure and feeding ecology have coevolved across related lineages.

Physical Description

Adult wreathed hornbills possess black plumage, black legs and feet, pale yellow bills and bare reddish skin around the eyes. Their white tails and gular markings contrast sharply with the dark body. Sexual dimorphism is evident: males exhibit bright yellow throat skin and a white neck, while females show blue throat skin and overall darker plumage. Young birds possess less distinct differences, with colouration and gular pigmentation becoming more pronounced with age.
They are medium-sized hornbills, with adults achieving notable body length and mass. Their heavy bills and large casques are supported structurally by the fusion of the first two cervical vertebrae, a feature typical within the family.

Bill Morphology and Casque Function

The bill casques of hornbills consist of lightweight, air-filled chambers encased in keratinous layers. In the wreathed hornbill, the upper bill is marked by serrated ridges near its base, which grow forward and periodically shed as the bird ages. Various functions have been proposed for the casque, including:

• Amplification of vocal calls
• Reinforcement for physical pounding
• Enhancement of courtship displays
• Visual signalling of age and dominance

These selective pressures collectively contribute to the diversity of casque formations seen across hornbill taxa.

Distribution and Habitat

The species thrives primarily in tropical evergreen forests, extending from southern Bhutan and Northeast India through Bangladesh and mainland Southeast Asia into Sumatra, Java, Borneo and smaller Indonesian islands. It has been observed at elevations reaching several hundred metres depending on region.
In Northeast India, the bird inhabits both untouched and selectively logged forests from Assam’s Nameri National Park to Namdapha National Park in Arunachal Pradesh. Seasonal movements occur between lowland breeding areas and higher-elevation non-breeding zones. Surveys in Bhutan and Myanmar indicate scattered but consistent presence, including flocks numbering up to 50 individuals.

Behaviour and Social Ecology

Wreathed hornbills are highly social and most active during early morning foraging periods. Field studies in Pakke Tiger Reserve show that birds rest during midday heat and resume feeding in the afternoon. They typically form larger flocks than other sympatric hornbill species, with group sizes in some regions exceeding 60 individuals.
Hunting pressure influences population density, as shown in Arunachal Pradesh where heavily hunted areas display significantly lower numbers. Although capable of long-distance flights between islands and forest patches, the species is not migratory.
GPS-tracking research reveals extensive daily movements during the breeding season, often several kilometres per day, illustrating the bird’s importance in maintaining ecological connectivity through seed dispersal.

Vocalisations

The primary call is a loud, double-noted yelp likened to coo-cuk or wuff-wurff. Typically delivered in sequences from perches or during flight, the second note is more forceful and carries farther. Calling involves a distinctive posture in which the bird thrusts its head backward, displaying the brightly coloured throat sac. Additional vocalisations include low-pitched, bisyllabic barking sounds used in social contexts.

Diet, Feeding Strategies and Seed Dispersal

The species is predominantly frugivorous, consuming large fruits—especially figs—and a higher proportion of drupe-bearing species than many other hornbills. Opportunistic feeding on insects, snails, crabs and small reptiles increases during breeding periods.
Wreathed hornbills forage mainly in the forest canopy but descend when necessary to gather fallen fruits or small prey. Seasonal variation in fruit availability prompts long-range flights to track productive feeding areas.
Their feeding behaviour employs ballistic food transport, in which the bird grips the fruit at the bill tip and throws its head back to swallow the item whole. This technique allows exploitation of large fruits inaccessible to smaller frugivores and ensures whole seeds pass through the digestive tract undamaged, thereby enhancing germination prospects. Their role as primary long-distance seed dispersers is fundamental to maintaining tropical forest diversity and structure.

Reproductive Biology

The wreathed hornbill forms monogamous pairs and exhibits strong biparental care. Nesting occurs in natural tree cavities—usually large ovals—located in mature forests or degraded foothill habitats. Nest heights vary widely but are typically positioned well above ground level for protection.
Females seal themselves inside the cavity using mud or droppings, leaving only a narrow slit for receiving food from the male. She incubates a clutch of one to three eggs for approximately forty days and normally raises a single chick to fledging after a nesting cycle lasting between 111 and 137 days. Both parents remain with the juvenile for months following fledging, reinforcing pair bonds and survival prospects.

Threats to Survival

Major threats to the species include habitat loss through illegal logging, forest fragmentation and agricultural expansion, along with direct hunting. In parts of Arunachal Pradesh, local communities traditionally hunt wreathed hornbills for food, medicinal use of gizzards and fat, ornamental feathers, and casque pieces for ceremonial headgear. Hunting for sport and market trade further exacerbates population declines.
The combination of slow reproductive rates, specialised nesting requirements and reliance on intact forest makes the species particularly vulnerable. These pressures have contributed to its classification as Vulnerable on the IUCN Red List, with population numbers continuing to decline across much of its range.