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Animal Fact Sheets

Range Map

Stable in the Wild


(Aceros cassidix)

Classification and Range

Hornbills are classified in the order Coraciiformes, which includes kingfishers, todies, motmots, bee-eaters, rollers, hoopoes and other related species. The 54 species of hornbills are further classified into the family Bucerotidae.

The Sulawesi hornbill is endemic to the Indonesian island of Sulawesi and smaller nearby islands.


Red-knobbed hornbills inhabit primary lowland forest and forest edge from sea level to about 3,600 feet (1,097 m) in elevation.

They occasionally range up to 5,900 feet (1,798 m) in elevation. Radio-telemetry studies have shown that red-knobbed hornbills may cover as much as 23 miles (37 km) per day, passing through degraded habitat in search of fruiting.

Physical Charateristics

The adult male's crown and back of head are reddish brown, face and neck are pale red or cream-colored, body and wings are black, and the tail is all white. A male's bill is yellow with orange-brown ridges ("chevrons") across the base of both mandibles, and features a tall red wrinkled ridge (also called the casque ridge) on the upper mandible near the eyes. The skin around the eyes is pale blue and the eyelids are dark blue. The bare throat skin is dark blue with a black band through the lower edge and turquoise skin below the band. The male has orange or red eyes, while legs and feet are black.

The adult female is smaller than the male, with similar coloring. The female's casque is yellow, while the head and neck are all black. The female's throat skin has a smaller black band and the eyes are brown or orange.

Both sexes of immature red-knobbed hornbills have plumage like the adult male when first emerging from the nest cavity. However, their casque ridge is undeveloped and the bill is pale yellow with a red wash at the base. Juveniles have pale facial skin and dark brown eyes with a yellow rim. At 10-13 months of age, the casque of juveniles begins to develop and the female begins to molt into adult head and neck colors (i.e. black). The juvenile male's plumage remains the same with the casque growing larger and redder.

Life Span

Life expectancy in the wild could be approximately 20-35 years. Researchers need information from long-term banding studies to accurately know life expectancy.

Historical records of red-knobbed hornbills in captivity provided misleading information, as husbandry issues were underdeveloped and birds died after just a few years. Presently, the oldest living bird in captivity is a wild-caught male that a zoo acquired in 1989. Because it was wild-caught, its exact age is unknown. Life expectancy in captivity probably exceeds that of wild birds. With improved husbandry, more information on longevity will become available on captive-hatched birds.


In the wild: Various fruits (especially figs) are the major part of their diet. Red-knobbed hornbills also eat small invertebrates as a small part of their diet.

At the zoo:Soaked (dried) figs, apples, papayas, bananas, grapes, blueberries, pear, melon, tofu, and cooked yams.


Sulawesi red-knobbed hornbills probably reach sexual maturity at 5-6 years. In Sulawesi, the breeding season normally occurs from June to September. If the first clutch fails, the birds will re-nest and try again in July or August. Most North American captive births result in hatchings between April and June.

The birds find a natural cavity (caused by lightning strikes, natural decay, etc.) in a large tree and the female seals herself inside. She creates a mixture of feces, food, and feathers into a clay-like substance to seal off the enclosure. A narrow vertical slit in this hard wall provides space for the female to defecate and the male to regurgitate food to the female (and nestlings). She remains inside the nest, incubating two to three white eggs for approximately 30-35 days. During incubation, the female depends entirely on the male to provide her with food. After hatching, the female remains in the nest, brooding the chicks for approximately another 90 days.

Life Cycle

In the wild, the chicks emerge from the nest some 30-40 days after the adult female has exited the nest cavity. It is rare that more than one chick successfully fledges. After confinement inside the cramped nest for as much as 130 days, the fledgling is not a strong flyer. It takes a day or two of exercising its muscles to enable the fledgling to keep up with its parents.Parents continue to feed the juvenile as they forage together in the forests.

In the tropics, food resources vary with space and time. Not all trees provide fruit during the same period of time and fruiting trees often grow far apart. During the non-breeding season, up to 50 hornbills may feed together in the same tree. Eventually, juveniles begin eating on their own. Adults return to the nest in the next breeding season, leaving immature and unpaired birds to roam among fruiting trees.

Toucan or Hornbill?

While toucans and hornbills share many physical characteristics, they are two completely different families of birds. Many people look at hornbills and immediately call them "the Fruit Loops toucan." This confusion is understandable. Both groups of birds have long, sometimes colorful bills. They both nest in cavities in tropical regions, and feed predominantly on fruits. However, this is where the similarities end.

Toucans live only in Central and South America; hornbills live only in Africa and Asia. Toucans are more closely related to woodpeckers, while hornbills are more closely related to kingfishers. The similar appearance of toucans and hornbills is an excellent example of a phenomenon called convergent evolution. This theory hypothesizes that two or more different species from different families and geographically separated locations have adapted similarly to fit an available niche in nature.

An Impenetrable Bond

Because the female depends so much on the male to provide (food) for her and the nestlings, courtship occurs throughout the year to build and maintain strong pair bonds. The male and female invest much time developing this bond, so it is to their advantage to remain together year after year, returning to the same nest site to breed and raise their young.

Location at the Zoo

Sulawesi red-knobbed hornbills are on exhibit in the large enclosure north of the Conservation Aviary in the Temperate Forest. The Temperate Forest also includes the Family Farm, Bug World, Wetlands, and Asian Cranes. Other birds on exhibit in the Conservation Aviary include: various pheasant species, curassows and trumpeters from South America, and several softbills (jays, laughing thrushes, turacos, whistling thrushes, birds of paradise, mynahs).

Conservation Connection

Red-knobbed hornbills are not an endangered species and are common throughout their range. Other species of hornbills are not so fortunate, as at least four species are listed as endangered.

The Sulawesi red-knobbed hornbill is endemic to the island of Sulawesi, which is slightly larger than the state of North Dakota and encompasses just 73,057 square miles (189, 216 km2). Therefore, the red-knobbed hornbill's habitat is restricted and the small size of Sulawesi limits its future survival. Today, the biggest threat to this hornbill is logging, which results in loss of habitat. Excessive logging removes the required large trees with naturally occurring cavities. To fully assess the status of this species, researchers need more studies to determine if the population is stable or declining.

Hornbills are important because they help disperse seeds throughout the forest. They regurgitate larger seeds, and pass smaller seeds through their feces. It may be that forests need hornbills as much as hornbills need forests. The presence of nesting hornbills is a sign of a healthy Asian tropical rain fore.

Woodland Park Zoo is Helping - With Your Support!

Each in-situ project supported by the zoo aims to provide a broad, holistic approach to conservation, encompassing research, education, habitat and species preservation. This includes comprehensive, cooperative strategies to link the needs of animals with the people who share their ecosystems.

Woodland Park Zoo (WPZ) supports Dr. Randall Kyes of the University of Washington. Each year, Dr. Kyes offers a lengthy field biology course to students from Manado University in northern Sulawesi. They live for several weeks in Tangkoko Dua-Sudara Nature Preserve, learning various field techniques while observing Celebes black apes. The most obvious avian species in this preserve is the red-knobbed hornbill, which the students learn about. It is hoped that through these field classes, local Indonesians will take on future responsibility as guardians of their local flora and fauna.

Since 1999, WPZ staff, volunteers, members and friends have adopted more than 255 hornbill nests in southern Thailand. This is a win-win situation for all involved: the hornbills get protected, the researchers obtain data, and the villagers get much needed cash to improve their lives.

An outcome of the above program was the construction and staffing of the Conservation-Education Center in Tapoh Village, Narathiwat Province in southern Thailand. WPZ has supported this Education Center since 2001.

How You Can Help!

The effort to save animal species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in WPZ and other conservation organizations of your choice. Let your elected representatives know your views on protecting endangered species and wild habitats. Please do not buy products made from wild animal parts.

Find out how you can adopt a hornbill nest at the Hornbill Nest Adoption Program page. One hundred percent of the adoption money (at a price of $150 per nest per year) goes directly to the villagers who guard nests in neighboring Budo-Sungai Padi National Park. Along with protecting the birds and nest sites, they collect valuable data for the Hornbill Research Foundation. At the end of the breeding season, nest results are sent to each adopter. Included with these results are colored photos of the birds at the nest and the local villager who protected it.

Sources and Suggested Reading

del Hoyo, J., Elliot, A. & Sargatal, J. eds. 2001. Handbook of the Birds of the World, Volume 6. Mousebirds to Hornbills. Lynx Edicions, Barcelona, Spain. 589 p.

Kemp, A.C. 1995. The Hornbills. Oxford University Press, Oxford, UK. 302 p.

Kinnaird. M.F. 1995. North Sulawesi: A Natural History Guide. Wallacea Development Institute, Jakarta, Indonesia. 83 p.

Kinnaird, M.F. & O'Brien, T.G. 1993. Preliminary observation on the breeding biology of the endemic Sulawesi red-knobbed hornbill (Rhyticeros cassidix). In: Tropical Biodiversity. 1:107-112.

Kinnaird, M.F. & O'Brien, T.G. 1999. Breeding ecology of the Sulawesi red-knobbed hornbill, Aceros cassidix. In: Ibis 141: 60-69.

Kinnaird, M.F., O'Brien, T.G. & Suryadi, S. 1996. Population fluctuation in Sulawesi red-knobbed hornbills: tracking figs in space and time. In: Auk 113(2): 431-440.

Kowalczyk, E. 2006. North American Regional Studbook: Genus Aceros. (unpublished but distributed to ISIS and AZA facilities). 114 p.

Michi, H. 1993. Der Celebeshornvogel. Gefierderte Welt. 117(3): 78-83.

Poonswad, P. 1993. Forest flagships. In: World Birdwatch 15(3): 14-17.


Red-Knobbed Hornbill Taxonomy

Phylum: Chordata
Class: Aves
Order: Coraciiformes
Family: Bucerotidae
Genus: Aceros
Species: A. cassidix

Red-Knobbed Hornbill Fascinating Facts

  • Hornbills rarely drink standing water. They get most (if not all) of their moisture from the foods they eat!
  • Hornbills are often heard before seen. They lack covert feathers that cover gaps between flight feathers. In flight, the air goes through the quills of the large flight feathers creating a loud "whoosh, whoosh" sound as they fly above the canopy of the forest!
  • In Indonesia, the Sulawesi red-knobbed hornbill is known as "Burung Tahun," or the Year Bird. The red chevrons on the sides of the base of the bill are thought to tell the age of the bird with a new stripe acquired with each year. However, some of these plates shed or fall off, and are not an indicator of the bird's true age.