Rhinoceros Hornbill – Buceros rhinoceros

Rhinoceros hornbills are usually 99-125cm long (both male and female). The male usually weighs more with average weights of 2.4-3kg; the female is lighter with average weights between 2-2.4kg. 

These hornbills are very large, with black plumage, except for white thighs and vent; the tail is also white with a broad, black band. 

Rhinoceros hornbills are listed as Vulnerable on the IUCN Red List and have a declining population trend. Illegal logging and agricultural development are among the biggest threats to this hornbill species. This species is also impacted by hunting. It is caught for food, trade and the use of body parts (mostly the casque and tail feathers) in ceremonial dress. 

Male rhinoceros hornbills have large ivory-white bills with some bright orange at the base of the upper mandible. Yellow is present on the bill which is from the preening oil, and extends along 1/3 of the bill. They have a typical ‘horn bill’, which is reddish orange and has a horn-like shape. It has a thick black line along the rear edge, but thinner along both sides and curving to the front. Males have red eyes with black orbital skin. 

Male Javan Rhinoceros Hornbill (Buceros rhinoceros silvestris) photographed at Chester Zoo (May 2021)

Female rhinoceros hornbills are smaller and also have a smaller casque which doesn’t have a black line on it. Females have white eyes with red orbital skin. 

The rhinoceros hornbill subspecies have a few differences between them. The Borneo subspecies is generally smaller and have shorter, broader casques that are sharply upturned and curled at the tip. 

The Javan subspecies (Chester Zoo’s rhinoceros hornbills) have broader black tail bands and forward-pointing, straight casques, but also have some individual variation. 

The juveniles have smaller, casqueless bills. 

There are thought to be 3 rhinoceros hornbill subspecies. B. r. rhinoceros occurs in south Thailand, Peninsular Malaysia and Sumatra. B. r. borneoensis occurs in Borneo, and B. r. silvestris is found in Java. A fourth subspecies of B. r. sumatranus has been suggested for Sumatran rhinoceros hornbill, but they appear to be inseparable from their original grouping of B. r. borneoensis

Rhinoceros hornbills are found in the Sunda subregion, south Thailand, Peninsular Malaysia (Kalimantan, Sumatra and Java) Borneo, including Brunei and western Indonesia; they are locally extinct in Singapore (2001). 

They are found in extensive tracks of primary Sundaic rainforest; they extend into mature secondary forest and are occasionally seen flying over disturbed areas or plantations to and from feeding grounds. They can be found at sea level and coastal swamp forest into lower montane forest, recorded to around 1,400m elevation. 

They feed mainly on fruits, especially many figs, but also lipid-rich capsules and drupes. They will eat other fruits in different locations such as the tropical rainforest in southern Thailand. They will also be opportunistic and take animal food, often below the canopy, especially during the breeding season to get enough protein into the young. The prey they feed on includes quite a variety of different items, including invertebrate animals (insects), lizards, rodents, tree frogs, and bird eggs. 

A study from southern Thailand showed an average amount of food brought to the nest, and found around 72% of total food weight was figs, 24% was other fruits and 4% was animal prey. With around 63g/obs.hr delivered to nests. 

They are largely sedentary and are usually seen in pairs or small family groups, feeding high in the canopy of large forest trees. Outside of breeding season, they may travel in search of fruiting trees, particularly figs, and flocks of up to 25 birds. 

They have a largely aseasonal breeding season. Egg-laying has been recorded in January, March-June, September and November. In southern Thailand, females have been seen sealing their nests in March and a chick has been seen fledging in July. 

The nest is a natural cavity in a tree, averaging 4-46m high in the tree, most usually around 22m, mainly Dipterocarpaceae trees. 

The female will seal the nesting hole until only a narrow elongated slit remains. The male will feed her, and later the chick through the narrow slit remaining. The male will regurgitate fruits from its gullet; it carries animal prey into the nest in the tip of its bill. 

1-2 eggs are laid; the incubation is 37-46 days. The female will emerge from the nest 39-51 days after the chick hatches; the nestling period is around 52-90 days. Total nesting cycle in southern Thailand is 122 days plus/minus 10 days. 

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