Currently three subspecies are recognised: B. r. rhinoceros occurs in south Thailand, Peninsular Malaysia and Sumatra; B. r. borneoensis occurs in Borneo, and B. r. silvestris in Java.
Distribution: Sunda subregion; south Thailand, Peninsular Malaysia, Borneo, including Brunei and western Indonesia; locally extinct in Singapore.
Description: 99-125 cm. Male 2465-3000 g; female 2040-2330 g. Very large hornbill with black plumage except for white thighs and vent; tail white with broad black band. Male has large ivory-white bill with some bright orange at the base of upper mandible and yellow colouring from preen oil extended to about one third of the bill; the casque is the typical ‘horn” bill, with prominent reddish orange horn-like shape and black thick line along the rear edge, but thinner along both sides and curved to front. Eyes are red with black orbital skin. Female is smaller with a smaller casque, without black line on it; white eyes and red orbital skin. Borneo subspecies is generally smaller with shorter, broader casque sharply upturned and curled at tip; Javan subspecies has broader black tail band and forward-pointing straight casque, but with some individual variation. Juveniles have smaller casqueless bills.
Voice: The call in flight is a characteristic penetrating disyllabic ger-ronk that can be heard over several km, often as a duet. The male’s call near the nest is a regular deep ho-ok note, answered by the female’s similar, slightly higher and softer note. Wings give out a loud whooshing sound in flight.
Habits: Found in extensive tracks of primary Sundaic rainforest; extends into mature secondary forest, and occasionally seen flying over disturbed areas or plantations to and from feeding grounds. From sea level and coastal swamp forest into lower montane forest, recorded to 1,400 m elevation. Feeds mainly on fruits, especially many figs, but also lipid-rich capsules and drupes. In a tropical rainforest of southern Thailand, among non-fig fruit Polyalthia sp (Annonaceae), Aglaia spectabilis (Meliaceae) and Oncosperma horridum (Arecaceae) are dominant. Also takes animal food on an opportunistic basis, often below the canopy, and especially during the breeding season to feed protein to the young. Prey includes invertebrate animals as well as lizards, rodents, tree frogs and bird eggs. In a survey from southern Thailand published in 2011 it was found that of food per weight brought to the nest, 72% was figs, 24% other fruits and 4% animal prey, with 63 g/obs.hr delivered to nests. It is largely sedentary and usually seen in pairs or small family groups feeding high in the canopy of large forest trees; outside of the breeding season it may travel in search of fruiting trees, particularly figs, and flocks of up to 25 birds, often mainly immatures, might form.