HORNBILLS: CHARACTERISTICS, BEHAVIOR, NEST-BUILDING

HORNBILLS

rhinoceros hornbill

Hornbills are a kind of bird named after their the large horn-like bills found on most species. . There are 54 species of hornbill: 23 species living in the savannahs and forest of Africa and 31 species in Asia, living mostly in tropical rain forests. Only four species are found east of the Wallace Line. [Source: Michael Long, National Geographic, July 1999]

Hornbills first appeared in the fossil record about 15 million years ago. They are found in many myths of tribes on Southeast Asia and Indonesia. Borneo hill tribes regard rhinoceros hornbills as deliver of souls to the afterlife. In western Borneo, a celebration honoring hornbills is held every five to seven years. On Sumba, they are symbols of fidelity.

Hornbills are found only in the Old World. Toucans are regarded as their New World equivalent. The largest hornbill are the size of turkeys. The smallest is the size of doves. Many large ones have horn-like casques on their bill. Some bird live as long as 45 years.

Many hornbills are endangered or threatened as a result of deforestation, loss of habitat and hunting for their bills, feathers and meat. Some have fallen prey to poisons left out for other animals. Other are taken by poachers who can sell the chicks of arre species of up to $1,000 a piece.

Websites and Resources on Birds: ; Essays on Various Topics Related to Birds stanford.edu/group/stanfordbird ; Avibase avibase.bsc-eoc.org ; Avian Web avianweb.com/birdspecies ; Bird.com birds.com ; Birdlife International birdlife.org ; National Audubon Society birds.audubon.org ; Cornell Lab of Ornithology birds.cornell.edu ; Ornithology ornithology.com ; Websites and Resources on Animals: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org

Hornbill Characteristics

Hornbill have long curving bills that are mostly yellow and can reach lengths of 13 inches. The bill is an integral part if the hornbill’s skull and is used by the bird to feed, fight, preen, make nests and keep snakes from attacking the vulnerable parts of their body. Bill development is often an indicator of sex and age. Many hornbills have prominent eyelashes.

Many hornbills have prominent casque. The casque is a hollow structure located on top of the bill. The casque seems to serve primarily as a reinforcing ridge along the top of the bill. But may also play a role is sexual selection and amplify the bird’s calls. It may also be used by males to fight with other males. In many species it has been modified into a hollow resonator. The casque of helmeted hornbill it is a block of solid ivory and helps make the skull 11 percent of its body weight. The shape of the casque is often the easiest way to determine species.

Hornbills have strong neck muscles that support the head and two fused vertebrae in the neck, a feature unique among birds. These features stiffen and strengthen the neck, give power to the bill and turn the head into a kind of pick axe

seeds dispersed by hornbills

Hornbills have bare facial skin and long eyelashes. Their eyes are often brightly colors with greens, reds, yellows and blues. The throat skin may form wattles, or inflation sacs. They have strong claws which allow then to grip the sides of trees like woodpeckers.

The feathers of hornbills or mostly black, gray or brown. Some species have white feathers that give them distinctive markings. Some species have long tail feathers. The loud whooshing noise emanating from some large hornbills as they fly is produced by gaps in the hornbill’s wing feathers and air being compressed in these gaps. Large hornbills lack feather that allow for smooth air flow. The wing beats of some species can be heard a half mile away.

Hornbill Behavior

Most hornbills are sedentary and live in defined territories. All the species save one that live in Africa live in savannahs and grasslands. Most of those that live in Asia dwell in the forests. Sometimes the forest dwellers fly beyond their territories to search for fruit. Sometimes the savannah dwellers migrate during the wet and dry seasons.

Hornbills make loud calls. Each species has its own distinctive calls. Helmeted hornbills of Malaysia produce noises that sound like hooting and laughter. The great Indian hornbill roars. Von der Decken’s hornbills clucks. Some species produce exaggerated displays while calling. The largest hornbill, the five-kilogram south ground hornbill, produces a booming deep bass call that can be heard 2½ miles away.

Hornbills are generally monogamous. Many mate for life. On the Indonesian island of Sumba, they are symbols of fidelity. Pairs usually share and defend a territory that ranges in size from 10 hectares to 100 square kilometers. Copulation usually tales place during the last phase of nest building. A few species form groups whose goals are to defend the group territory and help a dominant pair breed.

Males are slightly larger than females but females are more courageous, choosing to fight monitor lizards and snakes that males back off from.

Hornbill Feeding

rufous-necked hornbill

Hornbills primarily feed on fruit, figs and insects. Many species collect fruit in their neck pouch and hide them in caches. Some have to ability to clasp fruit, insects and other food with the tip of their bill and deftly toss it in the air and catch it their gullet like a person catching a piece of popcorn in their mouth. As a rule hornbills don’t drink. They get all the water need from their food. Only four species have ever been observed drinking.

Some hornbills have a fairly diverse diet. Male great hornbills bring up to 13 meals of fruit a day to nesting females. One male was observed delivering 150 figs in one visit, regurgitated one after another, as well as beetles, snakes, giant scorpions, geckos, bats and young of other birds. Females reportedly like some variety to their diet and have refused food if they are brought to much of the same thing. In Africa, there are some ground species of hornbill that methodically search through their territories for living animals such as large insects, snakes and frogs.

Hornbills are important for seed dispersal and help spread the food they eat. They spit out the seeds of some fruit. Fig seeds are dispersed in their droppings. Because they have such a large gape (mouth interior) Great hornbills are able to transport and disperse seeds of trees in the genus Myristica, which tend to be too large for other animals to disperse. These trees rely on Great hornbills for seed dispersal since only a few other birds are able to ingest the seeds intact to later disperse. [Source: Spurthi Paruchuri, Animal Diversity Web (ADW) /=]

Hornbill Nests

All but two species of hornbills nest in tree cavities or rock crevasses that are sealed shut except for a narrow, vertical slit. In places were there are shortages of tree cavities hornbills often fight among themselves and evict other birds or even snakes or large monitor lizards to gain access to a cavity. Most nests are built in tree hollows. A typical one began as a hole pecked by a woodpecker that is enlarged by fungus. Later a bee colony moves in and the hole becomes larger after a bear scrapes it with his claws to gets honey from the bee’s nest.

Being unable to excavate their own cavity into a tree, hornbills pairs use pre-existing tree cavities. They compete with members of their species as well as members of other hornbill species, bees, wasps, monitor lizards, giant flying squirrels, and king cobras for nesting cavities within trees. Pairs attempt to chase away competition, but if the pair becomes too stressed they abandon the cavity in search of another. Males are usually tasked with finding a suitable cavity, and the female has to approves it before it is used. Females only nest in cavities that have narrow entrances. They are often so narrow that they will struggle to enter or exit it.[Source: Ashlynn Pryal, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: When the female is ready to lay her eggs, she seals herself inside the cavity. A very narrow cavity entrance allows the pair to spend less time and energy sealing the entrance than if it were a larger opening. However, if the opening is too small for her to fit, the pair may peck around the entrance to make it larger so the female can get inside. The females seal themselves, with the help of their mate, inside the nest using mud, feces, and fruit peels.

David Attenborough wrote in "The Life of Birds", "The female hornbill is very fussy about the nesting accommodation. To suit her, a tree hole has to be reasonably spacious. It must also have a chimney at the top that will serve as a bolt hole if attacked. Once she has selected it, she invariably improves it by plastering over any crevices or smaller holes. The material she uses varies according to her species." After the females has made herself comfortable in a good nesting site the male brings lumps of soil moistened with his saliva and sometimes augmented with droppings, chewed wood and bark and other detritus. Together they build a wall of mud: he from the outside and she from the inside. The soil is applied with the side of the mouth. Among some species, the male swallows mud and regurgitates it in little balls to the female. First subsidiary entrances are sealed, then the main one is changed into a slit. Much of the work is done by the female. While she is doing this the male brings her food as well as more material for the plastering. Once the wall is complete the female is trapped inside the nest with only a small hole to outside through which to get food and communicate.

Life Inside a Hornbill Nest

The female hornbill is sealed inside. The slit is about a half inch wide: wide enough to pass food through but narrow enough to seal out potential predators such monkeys raptors and other predators that feed on eggs and young birds. If a snake tries to slither the female inside can fight it off with her bill. The sealed nests also act as a chastity belt.

The female of small species lay up to six eggs and incubates them for 25 days. The females of large species lays two eggs and incubates them for 45 days. During this time and after the chicks are born the male is responsible for supplying food. After the chicks have hatched the male may make as many as 70 feeding trips a day, bringing the female and the chicks geckos, seeds, insects, frogs slugs, berries and occasionally snakes. The males of some large forest species swallow fruits and regurgitate them one at a time to the female.

The female ejects her excrement out the opening. She does this by putting her rear end to the hole and shooting her excrement as far as possible. This is done not only to keep the nest clean, reducing the chance of disease, but also to prevent predators from locating the nest by the smell of the excrement. In most cases it takes the chicks a while to master this technique and before they do the female picks up the excrement and toss it out the slot or uses it make repairs on the wall.

Female hornbills remain trapped inside the nest for three to five months, while their eggs are incubating and the chicks grow up. They molt while in the nest, casting out their flight feather shortly before laying the eggs and regrow them before emerging from the nest.

During their time in the nesting, the female and her young are totally dependent on the male for food. If something happens to him, often the whole family perishes. Among species that form nesting groups, the entire group gathers food for the nesting female. Among Rufous hornbills, non-breeding birds in addition to the male may provide assistance by bringing fruit to a female incubating her eggs. Among some African species, when the young chicks grow to a large size the female turns her nest into a split level with the upstairs for her and the downstairs for her chicks.

Hornbill Young Leave Their Nest

The period of confinement for the chicks ranges from around 50 to 90 days. The females of some species breaks out before the chicks fledge to help the male bring back food. Others break out when the chicks fledge. Sometimes the chicks help break down the wall two weeks to a month after the eggs hatch so the female can escape and then help rebuild the wall. In this case, both the female and male work full time collecting food for the chicks which grow up quick and get bigger and hungrier everyday.

When hornbill chicks are 45 to 80 days old their voice changes and parents respond by not bringing food. This encourages the chicks to break out of their walled nest. Typically they break a hole in the wall first and poke their head out and scan the outside world for the first time. It often takes a couple days for it get enough courage to leave. It has fly to leave.

When the chicks are ready to fly they break through wall while its parents squawk loudly in encouragement. Sometime simply getting out takes some effort because by this time the chicks have grown quite large. Often the maneuver one wing out first and pop out and land on branch. Later, with more encouragement from their parents and a little tough-love prodding, they learn to fly.

Image Sources: Wikimedia Commons

Text Sources: Animal Diversity Web animaldiversity.org ; National Geographic, Live Science, Natural History magazine, David Attenborough books, New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Discover magazine, The New Yorker, Time, Reuters, Associated Press, AFP, Lonely Planet Guides, Wikipedia, The Guardian, Top Secret Animal Attack Files website and various books and other publications.

Last updated February 2025