Description
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.
Range and Habitat
Great hornbills are found in India, Southwestern China, Bangladesh, Western Ghats of India, Thailand, Mainland Southeastern Asia, Malaya, and Sumatra.
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.
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.
Behavior
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. |
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Great Hornbill Nest Camera: Courtesy of St. Louis Zoo WMP Streaming Video (199mb, 24 minutes) |
Conservation 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.