Great Hornbill (Buceros bicornis)
SSP Manager: Melissa Ramsey - San Diego Zoo
The great
hornbill is the most widely kept and largest Asian hornbill in North American
zoos. Like all hornbills, the great hornbill has fused axis and atlas
vertebrae. The have long, heavy bills with a light, hollow casque reaching up to 7.5 inches on the
upper mandible. The casque is rectangular in cross section, double-pointed
in front, round in back, and concave or convex on top. Great hornbills
have bristles around the eyes that resemble eyelashes. Their toes are
syndactylous. Their flight is often noisy as air rushes through the bases
of the flight feathers, which are not covered with stiff coverts. The
plumage is black with patches of white on the neck, abdomen, wings, and
tail; the tail has a subterminal black bar. Preen-gland oil provides a
yellow stain for the bill and some of the white areas.
Great hornbills
are sexually dimorphic with the female having a pearly white iris and
pink to bright red bare circumorbital skin. The male has a deep red iris
with the skin surrounding the eye being black. It has also been noted
that the posterior surface of the casque in males is black, while the
same area in females is red. Males in addition are typically slightly
larger than females, although there can be some overlap in size.
Immature
great hornbills of both genders can remain in the male coloration for
up to four years; although some changes may be noticed prior in the color
of the iris and the color of the back of the casques. The casque does
not begin to develop until the birds are approximately six months in age.
Adult great hornbills reach a height of three to three and a half feet including tail and a possess of wingspan reaching up to 62 inches. The male weighs in at approximately 6.5 pounds, while the female reaches approximately 5.75 pounds. The great hornbill has an estimated life span of 35 to 40 years.
Status
Great hornbills
are listed as Appendix I of CITES, and as "vulnerable" in the
Red Data Book. Sizes of extant free-ranging populations are not known,
however Asian hornbills have been designated as a priority taxon for worldwide
concern and more surveys are being initiated. Although actual numbers
can not be given, the decrease in their habitat is well-documented and
the indication is that the populations are similarly decreasing. Hunting
in Indonesia and India for food and medicine has had an impact on the
population, although the primary cause for decline is the deforestation
of habitat leaving no insufficient food sources and nesting cavities.
Although there are few wild preserves large enough to support viable populations of the larger species of hornbills, there have been documented cases of hornbills re-colonizing areas that have been logged within the past five to thirteen years. The adaptibility may assist with the wild population being sustained in the future. Governments and private conservation groups are working to help great hornbills. Habitat has been protected for the hornbills and the fig trees that comprise the majority of their diet. In Thailand, local people are paid stipends to guard hornbill nests.
Range
Great hornbills
are found in India, Southwestern China, Bangladesh, Western Ghats of India,
Thailand, Mainland Southeastern Asia, Malaya, and Sumatra.
Habitat
The habitat
is primarily the canopy of tall evergreen diptocarp and moinst deciduous
forests, ranging from elevations of 600 meters to 2000 meters. Deforestation
is the main threat to the survival of the great hornbill as it eliminates
both food sources and sites for breeding.
Vocalizations
Great hornbills have a very loud, distinctive call which is typically uttered at the onset of breeding season or when the birds return to the roost. These vocalizations, which can be heard over long distances in the dense forests, can be used in territory defense and for maintaining contact. The male and female can be heard in frequent dueting and the calls can often be distinguished by the differing pitches.
Reproduction
Great Hornbills form a monogamous, territorial pair. The nests are made in natural tree cavities, the trunks of dead trees, or
the primary limbs of living trees. When the female is ready to lay her eggs, she will seal herself into the nest using feces,
mud, wood bark, and food debris. A small slit is left in the sealed cavity for food to be passed into the cavity and fecal material to be expelled.
The clutch of one to two eggs will be incubated for 38 to 40 days prior to hatching. The male will make approximately five visits to the nest per day to regurgitate food to the female and the young.
As the chicks continue to grow, the nest will get crowded, allowing the female to exit the cavity and reseal the nest until the chicks are ready to fledge about one to two weeks following. After the chicks have fledged, the parents will continue to care for them until they are approximately four to five months old. In captivity, the female has been reported to remain in the nest until the chicks have fledged. This could be attributed to an abundant food supply making it unnecessary for her to join the male in the search for food.
Diet
The diet in the wild consists of primarily fruit, but also will include small mammals, lizards, snakes, and insects. In India, it has been reported that the diet consists of up to 73% figs. Additional research has shown that great hornbills play a significant role in dispersing seeds from numerous fruit trees. The seeds are deposited in the fecal material after the remainder of the fruit has been digested.
In captivity, the diet is composed of low-iron pellets, various types of fruits and vegetables, insects, and rodents. Like several other species, the great hornbill can be susceptable to iron storage disease. According to several reports the great hornbills have not been observed to drink water, instead obtaining their fluids through the diet items.
Medical - Squamous Cell Carcinoma
The captive population of giant/Indian hornbills (Buceros bicornis) reached a maximum population in 1983 of 79 birds but currently reports less than 50 birds in the SSP managed population. Since 1990, multiple reports (n=12) have documented invasive squamous cell carcinoma – the most recently in 2010 - of the casque with no gender predisposition. To date, no explanation has been found for the tendency of this neoplasia to occur in this location. Furthermore, extensive pathologic evaluation of both biopsies and post-mortem tissue has not determined an underlying infectious (bacterial, fungal, or viral) cause. To date, only B. bicornis has been identified at risk but the rhinoceros hornbill (B. rhinoceros) is sufficiently close taxonomically to warrant concern.
Plain radiography of the casque and skull in five standard views (both lateral, dorsoventral, ventrodorsal, and rostrocaudal) is the most sensitive tool for early detection of this fatal disease and should be considered annually. Digital images or copies of the radiographs should be submitted to the Veterinary Advisor for cataloguing and review to known SCC birds.
(Gamble, K.C. 2011. Squamous cell carcinoma in Buceros hornbills. In: Fowler, M.E., and R.E. Miller, eds. Zoo and Wild Animal Medicine, Current Therapy 7, in press.)
Coraciiformes Taxon Advisory Group - 
