Hornbills of Africa, Asia, and Indonesia

Colourful Birds with Big Bills and Strange Nests

Oct 31, 2009

Like the familiar showy Great Hornbill, Ground Hornbill, and Rhinoceros Hornbill, most hornbills are black and white with bright bills, eyes, and skin patches.

All hornbills are fairly large birds with the smallest being about thirty centimeters (a foot) long from the tip of the bill to the tip of the tail, and the largest more than a metre and a half (five feet) long. Some, like the Helmeted Hornbill, have tail feathers up to a metre long (three feet). Most hornbill species are black and white but their bills and bare skin patches are bright shades of red, orange, and yellow. The birds add this colour themselves using oil from the preen gland.

Hornbills are particularly memorable birds because of the structure called a casque located over the bill. The casque is strikingly large and brightly coloured in many species and makes the already large bill appear thick and oversized. Anyone who has observed nesting hornbills will remember their fascinating sealed nests as well.

What is a Hornbill’s Casque For?

It’s hard to imagine what the bulky casque on the upper bill of a hornbill is there for. In most cases it’s not as heavy as it looks: it’s composed of keratin, the same material that human fingernails are made of, and it’s hollow, with only slender supports inside. The Helmeted Hornbill’s casque is an exception: the front of the casque in this species is a heavy chunk of keratin called hornbill ivory.

Scientists think that hornbill casques have various functions, and these differ between species:

Hornbill Habitat and Diet

Most hornbills live in forests, however some are savannah species and a few prefer wetlands. Those that live in open savannah are meat eating predators, while forest species are often fruit eaters. Forest hornbills often search for fruit trees in large flocks, and are instrumental in spreading fruit seeds over large distances in their droppings.

Hornbill Nests – Cavity Fortresses

Hornbills nest in cavities, usually in trees. The female, sometimes assisted by the male, selects a nest site and proceeds to seal up the opening with mud. When the opening approaches being too small for her to fit through, she goes inside and continues her work, now using feces and food remains, and sometimes outside materials provided by the male. When only a narrow vertical slit remains, the nest is ready.

The female hornbill lays her eggs and tends the young, feeding them food brought by the male and passing soiled nesting material out through the slit. At the same time, she molts and begins to grow new flight feathers. In some species, she does not open the nest until the young are ready to fledge. In others, she removes the barricade when the chicks are about half grown and helps the male continue to feed the chicks while the chicks reseal the hole.

In up to a third of hornbill species, a from of cooperative breeding takes place, in which some males and young birds assist a breeding pair instead of breeding themselves. This lightens the feeding and nest cleaning duties of the males and increases the chances of nesting success.

The large ground hornbills are an exception to the usual hornbill breeding strategy. They do not seal their nests, nor do they remove soiled nesting material. Female Ground Hornbills don’t molt during the nesting period.

Hornbill Conservation

Hornbills have been hunted throughout their range for generations. People use them for food and traditional medicines, hunters use heads and feathers for camouflage, and various parts, particularly the beak and casque, are used in costumes and rituals. Hornbill ivory is prized as a carving material.

Today, hornbills are threatened by various things, notably hunting and habitat loss. Two species are listed as critically endangered on the IUCN Red List of Species, two are listed as endangered, and five are vulnerable.

Due to their large size, impressive appearance, and fascinating nesting habits, hornbills are particularly interesting birds. They are often seen in captivity.

Sources:

Firefly Encyclopedia of Birds. Perrins, Christopher ed. Buffalo: Firefly Books, 2003

The copyright of the article Hornbills of Africa, Asia, and Indonesia in Wild Birds is owned by Rosemary Drisdelle. Permission to republish Hornbills of Africa, Asia, and Indonesia in print or online must be granted by the author in writing.