Cambodia & Nature: Everything You Need to Know About the Great Hornbill

Great hornbills (Buceros bicornis) are widespread across Asia, found mainly in forest canopies, and are occasionally spotted in neighborhoods of the Cambodian capital, perched on gutters or in a few trees. This isn't migration or a new range expansion. While hornbills are threatened by the gradual loss of their natural habitat, the ones seen in the capital are most likely birds that have escaped from their owners.

Great hornbill, Buceros bicornis

Great Hornbill

The great hornbill (Buceros bicornis), also known as the concave-casqued hornbill, is one of the largest members of the hornbill family. It is found across the Indian subcontinent and Southeast Asia. Its impressive size and coloring give it a prominent place in many cultures and tribal rituals. The great hornbill has a fairly long lifespan, living up to 50 years in captivity. It is primarily frugivorous but opportunistic, and may prey on small mammals, reptiles, and birds.

Description

The great hornbill measures 95 to 130 cm in length, with a wingspan of 152 cm and a weight of 2 to 4 kg. Females are smaller than males and have bluish-white eyes rather than red, though the skin around the eye sockets is pink. Like other hornbills, they have prominent “eyelashes.”

The bird's most striking feature is the bright yellow and black casque atop its massive bill. The casque is U-shaped when viewed from the front, with a concave top and two ridges on the sides that form points at the front — hence the Latin epithet bicornis (“two-horned”).

Great hornbill, Buceros bicornis

The back of the casque is reddish in females, while the underside of the front and back of the casque is black in males.

The casque is hollow and has no known function, but is believed to be the result of sexual selection. Male hornbills are known to engage in “aerial casque-butting,” striking each other in flight. The male spreads the yellow secretion from the preen gland over its primary feathers and bill to give them their bright yellow color. The bill's cutting edge is black and has a serrated margin that wears down with age.

Wingbeats are heavy, and the sound produced by the birds in flight can be heard from a distance. Their flight consists of stiff wingbeats followed by glides with the wingtips spread and curved upward. They sometimes fly at great height above the forest.

Taxonomy

The species was formerly divided into two subspecies: cavatus, from the Western Ghats, and homrai, the nominate form from the sub-Himalayan forests. The Sumatran subspecies was sometimes called cristatus. Variation between populations mainly concerns size, with Himalayan birds larger than those in the south, and the species is now considered monotypic.

Hornbills have bones with hollow air cavities extending to the tips of the wing bones. This anatomical feature was noted by Richard Owen, who dissected a specimen that died at the Zoological Society of London in 1833.

Distribution and Habitat

Great hornbills are found in the forests of India, Bhutan, Nepal, mainland Southeast Asia, the Indonesian island of Sumatra, and northeastern India. The species' distribution is fragmented across its range in the Indian subcontinent and Southeast Asia.

On the subcontinent, they are found in a few forested areas of the Western Ghats and in forests along the Himalayas. Deforestation has reduced their range in many parts of India, such as the Kolli Hills, where they were recorded in the 1860s. Their distribution extends into Thailand, Cambodia, Myanmar, Malaysia, and Sumatra. Their habitat consists of dense forests in hilly regions.

Great hornbill, Buceros bicornis

Despite its wide range, the great hornbill occurs at low densities and is unevenly distributed. Its population is declining rapidly in many regions, including Cambodia. The conservation NGO Wildlife Alliance is helping stabilize populations in Cambodia by protecting vital habitat in the Cardamom Mountains and working to save the species from the illegal wildlife trade.

The home range of males is approximately 3.7 km² during the breeding season and approximately 14.7 km² for the rest of the year.

Food and Feeding

Great hornbills are generally observed in small groups, with larger groups sometimes gathering near fruiting trees. In the wild, the great hornbill's diet consists mainly of fruit. Figs are a particularly important food source. Vitex altissima has been noted as another significant food source. Great hornbills also feed on lipid-rich fruits from the Lauraceae and Myristicaceae families, such as Persea, Alseodaphne, and Myristica. They obtain all the water they need from their fruit diet. They are important dispersers of many forest tree species. They also eat small mammals, birds, small reptiles, and insects.

They forage along branches, moving in a hopping motion in search of insects, bird nests, and small lizards, tearing at bark and inspecting it. Prey is caught, tossed into the air, and swallowed.

Reproduction

During the breeding season (January to April), great hornbills become very vocal. They form duets beginning with a loud “kok” call given roughly once per second by the male, which the female then joins. The pair then calls in unison, blending into a rapid mix of “roars and barks.” They prefer mature forests for nesting. Tall, old trees — particularly emergents that rise above the canopy — appear to be preferred nesting sites. They form monogamous pairs and live in small groups of 2 to 40 individuals. Collective courtship displays involving up to 20 birds have been observed.

The female builds a nest in the hollow of a large tree trunk, sealing the opening with a cement made mainly of droppings. She remains sealed inside, relying on the male to bring her food, until the chicks are half-grown. During this time, the female undergoes a complete molt. The chicks are featherless and appear quite plump. The clutch consists of one or two eggs, which she incubates for 38–40 days.

Great hornbill, Buceros bicornis

Young birds show no trace of a casque. After the second year, the front edge separates from the culmen, and during the third year it becomes a transverse crescent whose two edges grow outward and upward, while the front section widens to reach the width of the back edge. Full development takes five years.

The Roost

Roosting sites are used regularly, and the birds arrive punctually at sunset from long distances, following the same routes each day.

Several large trees in the surrounding area may be used, with the birds choosing the highest, sparsely leafed branches. They compete for spots until dusk fully sets in. When sleeping, they draw their neck back and hold their bill tilted upward.

In Captivity

Very few hornbills are kept in captivity, and few breed successfully. Nesting females are extremely easy to capture, and wild-caught birds are mostly females. Breeding hornbills in captivity is notoriously difficult, with fewer than a dozen successful attempts recorded. Their extreme selectivity in choosing mates and their long, strong pair bonds make them difficult to maintain for breeding purposes.

In captivity, hornbills eat fruit and meat. A few have been tamed in captivity, but hornbill behavior in captivity is described as very tense. Captive specimens are largely inactive and bask in the sun with wings spread.

Conservation

Due to habitat loss and hunting in certain regions, the great hornbill is assessed as Vulnerable on the IUCN Red List of Threatened Species. It is listed under CITES Appendix I. Population declines have been recorded in many regions, including Cambodia. In Southeast Asia, the birds are frequently shot by poachers.

Cultural Significance

Tribal populations threaten the Indian great hornbill by hunting it for its various parts. The bill and head are used as amulets, and the flesh is considered medicinal. Young birds are considered a delicacy. Tribes in parts of northeastern India and Borneo use the feathers in headdresses, and skulls are often worn as decoration.

CG, courtesy of GibbonWoot