Hornbills are medium-sized or large birds that dwell in Asia and Africa and are usually found in the jungles. They can be recognized by their long down-turned bills, which are sometimes colorful. There are about 60 species of Hornbills, although some are critically endangered.
Description
Most hornbills are black and white, with chestnut or grey interspersed. Their legs and feet are short and rather weak, somewhat usual for fruit eaters.
Hornbills are known for their large bill, often topped by a large casque. They are recognized by their bold colors, various calls, and rushing wingbeats.
They are not related to toucans, although their appearances are similar. About half the species live in Africa south of the Sahara, half in southern Asia, and a single species in New Guinea.
Most species have long tails, especially the Long-tailed hornbill and the White-crested hornbill, while in the Helmeted hornbill, the central pair of tail feathers is up to a meter (3.2ft) in length. In most species of the genus Rhyticeros, the tail is short and pure white, and the ground hornbills also have short tails.
Hornbills have long eyelashes and stubby legs and toes, with broad soles and partly-fused toes. Hornbills reach sexual maturity between one (Tockus ) and six (Bucorvus) years, and they can live up to about 40 years in the wild.
Bills and Casque
Their most prominent and celebrated feature is the large bill, which normally bears a sizable, brightly colored casque. The bill is long and down-curved, with only the tips of the mandibles meeting properly in most species.
The enormous bills and casques seem useless to hornbills and often appear like an encumbrance. They feed by picking food up between the mandibles’ tips and tossing each fruit back into the gullet, where the stubby tongue can assist the swallowing. The bills also have cutting edges often serrated for breaking up food. Undigested remains, such as pips, are regurgitated or defecated, facilitating seed dispersal.
The large bill is supported by strong neck muscles and another useful adaptation. Hornbills have the first two neck vertebrae (axis and atlas) fused together.
The casque forms a narrow ridge that helps to reinforce the upper mandible. However, in some species, the casque is cylindrical, upcurved, or folded, and in some cases, it can be larger than the bill. The casque is light and made up of thin-walled hollow cells.
The casque is poorly developed in young birds. In adults, it is much larger and more elaborate in males. The casque is a light skin of keratin over a bony support. The casque is used in recognizing the age, sex, and species of an individual, but it also serves to amplify calls.
The casque is used by some of the larger birds, like the Great hornbill of southeast Asia and the Rhinoceros hornbill, to fight or knock down food.
The Helmeted hornbill has a straight, short bill that has a casque of solid keratin attached. This block of keratin weighs up to 10% of their body weight. It is carved by the indigenous Kenyah and Kelabit people of Borneo into earrings or belt buckles.
The ‘ivory’ block was also traded with Chinese travelers visiting Brunei, who would use it for carving and making belt buckles back in the 14th to 17th Centuries during the Ming Dynasty.
Breeding
Breeding seasons depend mainly on food choice, with insect-eaters breeding in the warm wet season, while forest fruit-eaters show little seasonality.
Courtship is done by the feeding of females and mutual preening before copulation in larger forest species. Calls are used to defend a territory, and displays may be shown by an interested male.
The size of the territory can range from as little as 25 acres for the Red-billed hornbill and as big as 39 sq miles for the Southern ground hornbill.
Most hornbills are monogamous, with each member sharing all aspects of the nesting cycle. However, some species use cooperative breeding in which some individuals, usually mature males, do not breed but help a dominant pair to rear their young.
This can be seen in groups of hornbills, with flocks of up to 25 individuals. Immature birds are colored very differently from adults. It is found in species as diverse in form and size as the Brown-backed hornbill, Southern ground hornbill, the White-crested hornbill, Bushy-crested hornbill, and the Philippine brown hornbill.
Nesting
The hornbill is famous for its unique nesting habits. Once courtship and mating are over, the female retires to a hollow tree and seals herself into the chamber with a substance made up of dung and pellets of mud.
The male assists in gathering these materials on the floor and swallows them. The small pellets of mud and saliva are then passed to the female, who remains inside the nest. The female plasters them on the sides of the entrance. The female will also use her droppings, mixed with food remains.
Once complete, there is only a slit-like window that is just big enough to receive the end of the bill. For the next six or eight weeks, the male feeds the female through this opening.
Food is brought to the nest either as single items held in the bill tip or as a stomach full of fruits which are regurgitated one at a time to the young. Food remains are passed out of the nest slit while droppings are forcibly expelled.
The female lays a few oval white eggs with finely pitted shells. In larger species, 1 or 2 eggs are laid, while in smaller species, there may be up to 7. Incubation takes between 25 and 40 days. While incubating, the female begins a complete molt and loses her flight feathers, and, for a time, is flightless.
Among many species (Tockus, Buceros, Rhinoplax, Bycanistes, Ceratogymna, Rhyticeros, Aceros, Penelopides, Anthracoceros), the female breaks her way out of the nest a week or more before the young are ready to leave.
With her feathers regrown, she helps the male feed the young. Once they feed, the young rebuild the entrance, an instinctive behavior. Once they are ready to fly, they will break out of the nest. Until then, they sit with their long tail clamped to their backs.
In other species, the male will continue to feed the female and the young until the end of the nesting cycle.
The nest is ventilated using convection from the slit and provides good insulation. A long escape tunnel is normally built above, which protects from predators.
Diet
The larger forest hornbills are mainly fruit-eaters, and they travel widely in search of good fruit. The irregular fruiting and dispersal of the food source mean that these species are not territorial and tend to gather in large flocks to find suitable food.
Most smaller hornbills are insectivorous, taking small animals and fruit when available. Most of these have permanent territories, but some African species have to fly to new areas to find food after the rainy season.
The White-crested and Helmeted hornbills are known to be sedentary. The white-crested hornbill searches the foliage and forest floor for prey, following troops of monkeys for animals scared out of the trees. The Helmeted hornbill excavates prey from rotten wood and loose bark.
Only the large ground hornbills are almost entirely carnivorous, using their pickax-like bills to take down large prey. Snakes, squirrels, hares, and even tortoises are no match for their bills.
A breeding pair of hornbills have been seen to swallow as many as 69 small fruits and carry them to the nest to be regurgitated. It was observed at one nest of a Silvery-cheeked hornbill that the male delivered an estimated 24,000 fruits, over 1,600 visits spanning the 120-day breeding cycle.
Any small animals are caught if discovered, and in several species, reptiles and rodents are especially sought during breeding as a source of protein for the young.
Behavior
In their native habitat, hornbills are active birds of the forest canopy. They can be seen leaping from bough to bough on the tallest fruit trees, balancing their weight against their large bill. They are large birds, and their flight looks sluggish.
In the morning and evening, the hornbill normally comes to the ground to feed, bathe, and collect damp earth. They can often be seen hopping around on the ground instead of walking.
With about 60 species of hornbill worldwide, it is no surprise that some have exceptional behavior. The Rufous Hornbill Buceros hydrocorax from the Philippines. This is one of the noisiest birds while in flight. Their loudly beating wings make a hissing, whistling sound as the air moves through the flight feathers.
Many large hornbills look huge while in flight. The Great Pied Hornbill Buceros bicornis and the Indian Pied Hornbill Anthracoceros malabaricus are both large, forming crosses against the sky as they fly overhead. The wings are long and broad; the head, neck, and bill stand out prominently in front; and the long, rounded tail trails behind. Flight progresses by a series of flaps and glides.
The two species of ground hornbill—the Abyssinian Ground Hornbill Bucorvus abyssinicus and the Southern Ground Hornbill B. cafer—spend their lives walking the grasslands of Africa, searching for food alongside other birds of the African plains such as the Ostrich, Secretarybird, and bustards.
Ground Hornbills
There are only two species of ground hornbills. Both of these can fly but choose to spend most of their time patrolling the ground.
The Southern Ground Hornbill Bucorvus leadbeateri feeds on reptiles, insects, and mice. The Abyssinian ground hornbill Bucorvus abyssinicus) follows cattle and fires to feed on small animals disturbed by them. The two species of ground hornbills also differ from all the others in not plastering shut the entrance to the nest. They make their nests in holes in cliff faces or cavities in trees or other high places.
Critically Endangered
Three species are Critically Endangered; the Sulu hornbill, Walden’s hornbill, and the Helmeted hornbill.
For more information on the three Critically Endangered species, please click here.
