Colours of Wildlife: Trumpeter Hornbill

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Trumpeter Hornbill

Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"

Trumpeter Hornbill by Willem

I'm not done with prehistoric critters by any means, but let's get back to the present just for an interlude. Here I present to you a portrait of one of my own all-time favourite kinds of birds, a Trumpeter Hornbill, Bycanistes bucinator. It is sometimes classified in the genus Ceratogymna along with some other large, forest hornbill species of Africa. In Afrikaans we call it a 'Boskraai' or 'Forest Crow' even though hornbills and crows are only very distantly related. It's just that these large, mainly black, forest-living birds reminded the first Boers who saw them of crows. Though I don't illustrate it here, the belly, rump, the tips of the wing feathers and of the outer tail feathers, are white, the rest of the plumage glossy black. These birds reach an overall length of 55 cm/22" and can weigh up to 900 g/1 lb. The species gets its name for its loud, trumpeting calls. It is closely related to the Silverycheeked Hornbill. Trumpeter hornbills inhabit well-wooded countryside with large, fruiting trees from South Africa northward to southern Kenya. The species avoids the main equatorial rainforest belt, where it is replaced by other hornbill species.

I fell in love with this species more than twenty years ago when I first saw them in the wild in the Lake St. Lucia region in northern Kwazulu-Natal. The coastal forests there sport several very large trees such as Water Berries or Wild Figs that bear the fruit these hornbills love. They occur in pairs or small groups, usually of related birds. They set out to feed every morning, flying from their roosting trees. They look extremely comical in flight. They have these enormous heads with huge beaks, stretched out ahead of them on their long necks, and then behind there comes this skinny little body and wings that look utterly inadequate to the task of keeping that huge head in the air – and yet, they manage! Their heads are not nearly as heavy as they look; much of its volume is the loose, shaggy head and neck feathers, and the bill with the enormous casque is also very lightly constructed. The casque is mostly hollow, with a fine internal structure of struts to strengthen it while keeping its weight minimal. But they do look completely top-heavy.

At the Saint Lucia reserve I also was fortunate to see a baby of this hornbill up close. It was a youngster that they were hand-rearing; I can't remember any more what happened to it or maybe its parents. But it was an extremely cute little thing, very confiding and engaging-looking, perched on its handler's hand. Even though its casque was only half-developed, its head already looked bigger than its body. The casque seems to grow from behind, extending further forward as the bird matures. Only adult males get the 'full' casque with a tip extending as far forward as the tip of the main bill; juveniles and females have casques with a blunt end about halfway down the length of the bill. In males, casque size and also shape can vary a lot between individuals. When a male is in breeding condition, the rear of his casque gets a reddish 'blush' from active blood vessels, as you can see in my painting.

Science still doesn't know exactly what the casque is for. It may turn out to have several uses. Being big and hollow, it might be a resonating camber which amplifies the hornbill's trumpeting calls. These are mournful, braying sounds somewhat reminiscent of a crying baby. The calls are far-carrying and must have some use in proclaiming the territory of a family group, while also making it easy for females in breeding condition to find males. The casque of the male is also likely used for display, the bigger-casqued males dominating those less well-endowed, making them the favourites of the females. Finally, the casque may help with temperature control. Its large surface area may be a good radiator of heat, which may help the hornbills keep cool in the often-hot tropical and subtropical forests they inhabit.

The huge bill is used as a delicate fruit-picking tool. Figs such as figs or berries are grasped in the bill tip and plucked from their twigs. The bird then throws its head back and tosses the item back into its throat to swallow. A larger fruit may be crushed in the bill first. Some fruits have large seeds which the hornbills regurgitate after digesting the pulp. These seeds, having had the treatment of a hornbill's digestive system, are primed for germination and so the birds play a valuable role in propagating forest trees. Though fruit comprises about 90% of their diets, trumpeter hornbills also eat some animal food such as caterpillars, spiders and other invertebrates, and even eggs and small chicks of other bird species.

In their breeding behaviour, trumpeter hornbills are typical for their family. They form strictly monogamous couples. The male calls, sometimes in flight, to show off to the female. Before nesting, he will bring her food items, to prove his commitment to providing for her. This is extremely important: a female will be utterly dependent on her mate once she's incubating her eggs. She seeks out a large cavity in a tree, and there she, with her mate's help, immures herself by walling off the cavity entrance with mud pellets sometimes augmented by her own droppings and some food items. In the end, only a narrow slit is left open. The male uses this to pass food into the cavity to the female. She loses her wing and tail feathers and grows a new set while inside. After the chicks have hatched, they will also squirt their droppings through the slit so as not to befoul the nest. The male now has to do heavy-duty food collection to provide for them all. The female remains with the chicks until they're ready to fledge, then they all break out. They can't fly well at first, and for five to seven days will stay in the vicinity of the nest. Then they will start flying out with their parents to feed. In captivity, this species can live for more than twenty years; life expectancy might be a bit shorter in the wild.

Trumpeter hornbills are still very widely ranging, common in suitable habitat, and tolerant of some human activity, but are likely to be impacted by ongoing deforestation over much of the continent. For the moment they are secure but they need to be monitored. We need to stop cutting down the big trees at any rate, for many reasons besides protecting the habitat of these (and many other) charismatic birds.

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