Form a superspecies with Great Hornbill, hybirdisation has been reported both in the wild and in captivity. On basis of larger size, bird from Sumatra have been suggested as a subspecies, B r.sumatranus , but appear inseparable from nominate. Currently three subspecies are recognized: B. r. rhinoceros occurs in south Thailand, Peninsular Malaysia and Sumatra; B. r. borneoensis occurs in Borneo, and B. r. silvestris in Java.
Size 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 coloring 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 side 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 trip; Javan subspecies has broader black tail band and forward-pointing straight casque, but with some individual variation.
Juvenile has smaller casqueless bill. 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 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.
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.
Form sea level and coastal swamp forest into lower montane forest,recorded to 1,400 m elevation. Feeds lipid-rich capsules and drupes. In a tropical rainforest of southern Thailand, among non-fig fruit Polyalthai (Annonaceae), Aglaia (Meliaceae) and Oncosperma horridum (Arecacae) are dominant.
Also takes animal food on an opportunistic basic,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 food per weight brought to was found to the nest, 72% was figs, 24% other fruits and 4% animal prey, with 63g/obs.hr delivered to nests.
It is largely sedentary and usually seen in pairs on 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 from.
The nesting season in the equatorial belt is largely aseasonal; egg-laying has been recorded in Jan, Mar-Jun, Sep and Nov. In southern Thailand, female seals her nest in Mar and a chick fledges in Jul.The nest in natural cavity 6-46 m (average 22 m) up in large and tall forest trees mainly of Dipterocarpaceae (42% of total 56 nest trees), particularly Hopea and Shorea probably rarely nests in limestone cliffs.
The female will seal the nesting hole until only a narrow elongated slit remains,through which the male will feed her and later the chick. 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 period is 37-46 days.
The female will emerge from the nest 39-51 days after the chick hatches; the nesting period is 52-90 days. Total nesting cycle in southern Thailand is 122 days plus/ minus 10 days, even longer than for sympatric populations of Great Hornbill.
