Hornbills

What is a hornbill?

Hornbills are tropical birds named for their unusually large, curved bills, some of which are adorned with a large casque, a hollow structure made from keratin.

Casques, which vary in size and color, serve a number of functions, such as attracting mates and resonating sound, making the birds’ territorial calls more audible. Casques may also provide support when the birds use their beaks to peel off tree bark or dig in soil for insects.

Some hornbill species don’t have casques, such as the red-billed hornbill, which was the model for the character Zazu in The Lion King. (The Walt Disney Company is majority owner of National Geographic Partners.)

Most of the 62 hornbill species spend their time in the trees, except for the family Bucorvidae, the ground-dwelling hornbills.

The largest hornbill, southern Africa’s southern ground hornbill, stands at three feet tall with a four-foot wingspan. The red-billed dwarf hornbill, found in East and Central Africa, is the smallest species, at just under one foot.

Hornbills inhabit a variety of landscapes, including forests, savannas, shrublands, and rocky and high-altitude areas. Almost all species nest in natural cavities, mostly in trees but sometimes on rocky cliffs. These omnivores may dine on anything from fruit and seeds to insects, reptiles, amphibians, and small mammals.

Courtship and reproduction

There are many courtship behaviors, such as clattering bills together or alternating calls in a sort of duet.

Many hornbill species are considered monogamous, but only Montiero’s hornbill of southern Africa is genetically monogamous, meaning neither the male nor the female mate with any other birds. A male will often bring food to its mate, sometimes for an entire year.

Once mated, most hornbill pairs will find an existing tree cavity, and the male will seal the female inside using its own dung mixed with soil or regurgitated food. The male will leave only a small slit, through which he’ll will deliver her food. Protected from predators in this private suite, she’ll generally lay two eggs, which will incubate for about 42 days.

Usually only one chick will hatch or, if both emerge, only one chick will usually survive. Great hornbills of Southeast Asia and Malayan wreathed hornbills have a 40-day egg incubation period, and will brood chicks for as long as four months in the mother’s lair.

About a week before the chick is ready to strike out on its own, the female will tear the door down and leave the shelter. The chick will rebuild the protective wall and stay inside by itself, while both parents provide their offspring with food. Chicks will then fledge after roughly 80 days.

Southern ground hornbills have a different strategy, living in small flocks of up to nine individuals. Only the largest male and female—the alpha pair—will breed, while the rest of the birds help rear the offspring.

Conservation status

Of the 62 hornbill species, 51 species are decreasing in population, eight are stable, and three are data deficient.

The forest-dwelling helmeted hornbill of Southeast Asia is critically endangered due to an illegal trade in the birds’ casques, which has led to an increase in poaching of wild birds. The helmeted hornbills’ casques are softer than ivory and easy to carve into trinkets, jewelry, and other decorative items.

Also critically endangered are the rufous-headed hornbill and Sulu hornbill, both of the Philippines. There are only about 50 Sulu hornbills left in the wild, victims of hunting, human land use, and climate change. In 2019, the International Union for Conservation of Nature launched a decade-long effort to save the Sulu.