Rhinoceros Hornbill and the Horned Guan: Birds and Their Features
Two Birds With Head Ornamentation
Like mammals, some birds have horn-like structures on their head. Two birds with interesting head ornamentation are the rhinoceros hornbill and the horned guan. The first bird has a large and impressive casque. The casque is orange and extends over part of the bird’s head and bill. It’s sometimes curled upwards at the tip like the horn of a rhinoceros. The animal's population is classified as vulnerable. The second bird has a thick and upright horn that’s bright red and contrasts beautifully with the glossy back feathers on the upper part of the body. Unfortunately, this species is endangered.
The word "rhinoceros" is of Greek origin -- "rhino" meaning "nose", and "ceros" meaning "horn." This means that the Rhinoceros Hornbill's name could be translated to "Nose Horn Hornbill!"— The National Aviary Website
Hornbill Family, Range, and Habitat
The rhinoceros hornbill has the scientific name Buceros rhinoceros. It belongs to the class Aves (like all birds), the order Bucerotiformes, and the family Bucerotidae (hornbills). The members of the hornbill family are large birds with big bills. Their casque varies in appearance. Some species have a large casque while others have just a bump on their upper bill or no visible cache at all.
The rhinoceros hornbill is found in Indonesia, Malaysia, and Thailand. It lives in the rainforest and emits a call that is often described as a "honk". The bird is sometimes heard before it's seen. The call can be heard in the video below.
Physical Features of the Rhinoceros Hornbill
Probably the first thing that most people would notice about the bird is its impressive casque. The casque sometimes looks like a third bill, especially when it's straight. If it's strongly curved upwards, it looks more like a horn. In a mature bird, it's a mixture of yellow, orange, and red in colour.
The males and the females have a casque of almost the same size (though the female's is slightly smaller), so the structure can't be used to tell them apart. If someone is close enough to see the bird's eyes, a male can be distinguished from a female. The male's eyes have a red iris (the part of the eye that surrounds the central pupil), as shown in the photo above. The females have a white iris and a red ring around the outside of the eye, as shown below.
The bird is mostly black in colour, with the casque providing a colourful highlight. The belly is white. The feathers at the top of the legs are white and have a fuzzy appearance. The long tail is also white but has horizontal black bands on both its upper and lower surface.
Facts About the Casque
According to the National Aviary, the casque takes up to six years to reach its final size. The beak and the casque are white at first. During its life, the bird frequently runs its bill (and the attached casque) over an oil gland under its tail during the preening process. This action gradually changes the casque's colour.
The casque is made of spongy keratin. Keratin is a protein in the human body as well as in birds. It's found in our skin cells, hair, and nails. It's also found in animal claws. The protein exists as fibres. The firmness of structures containing keratin in influenced by how compact the fibres are and by structural variations in the keratin molecules. The casque of the rhinoceros hornbill has a relatively low weight because of its spongy composition.
The casque of Buceros rhinoceros is believed to amplify the bird's calls. It's thought to act as a resonating chamber and to be significant in communication, especially during the mating process.
Diet and Feeding
The rhinoceros hornbill spends most of its life in the tree canopy. The bird is a good flier. It has an omnivorous diet. It eats a lot of fruit—especially figs—but occasionally eats small animals. Its beak is long but its tongue is short. It often grabs hold of its food with the tip of its beak and then jerks its head back to move the food into its throat.
The bird is an important distributor of seeds. Many seeds are unharmed during their journey through the animal's digestive tract, and some are even helped by the conditions in the gut. When the bird drops feces containing the seeds, they are able to germinate. Since the bird is often in a new place when this happens, it enables the plant to spread.
Rhinoceros Hornbill Reproduction
Rhinoceros hornbills usually mate for life. They have an unusual and interesting method of reproduction. After mating and shortly before the eggs are laid, the female finds a hollow space in a tree and enters it. The male and the female then build a wall of mud, regurgitated food, and feces to seal the female in the tree. A small opening is left, through which the male feeds the female.
Once her eggs are laid and hatched, the mother and her family stay in the tree until the youngsters are about three months old. The mother periodically drops the feces produced by the group through the chamber opening, which keeps the area reasonably clean.
About three months after the birth of the chicks, the female breaks out of the hole. The family—reportedly including the chicks—then rebuild the wall. The chicks stay in the hole for another three months and are cared for by their parents. The youngsters then break the wall and fly away.
The video below shows part of a mating display in the species as well as preening behaviour. It has no sound, but the behaviour is interesting to see.
Population Status of the Rhinoceros Hornbill
The International Union for Conservation of Nature (IUCN) maintains a Red List. The list describes species and categorizes their population status. Buceros rhinoceros has been placed in the "Vulnerable" category, based on a 2018 assessment. The population is said to be decreasing.
The rhinoceros hornbill lives in primary evergreen forest. The IUCN says that the bird is currently widespread within its range, but its total population is thought to be low. Unfortunately, its habitat is undergoing rapid deforestation. In addition, the bird is attractive to hunters. It's caught for food and for the use of its casque and feathers in ceremonial dress and events.
The bird lives in some protected areas. This is helpful, but it's not enough. The IUCN has proposed certain conservation actions, including the following ones.
- Determine the rate of contraction of the bird's range.
- Investigate the cause of range contraction.
- Attempt to protect the animal's habitat in the areas where it's most vulnerable.
- Restrict hunting of the animal.
Galliformes Order and the Cracidae Family
The scientific name of the horned guan is Oreophasis derbianus. It belongs to the order Galliformes and the family Cracidae. The order includes some birds that are familiar for many people, including turkeys, chickens, grouse, pheasants, partridges, ptarmigans, and quail.
The Cracidae family contains guans, curassows, and chachalacas. The animals live in Central and South America. The range of the plain chachalaca (Ortalis vetula) extends into southern Texas, however. Some members of the family have a casque or a knob above their bill.
Physical Features of the Horned Guan
The horned guan is an attractive animal. It can be seen in the video screen above and in the videos below. Unfortunately, the only suitably-licensed photos of the bird that I've found are of low quality. Some physical features of the horned guan are listed below.
- The bird has a white to pale-yellow beak, a white iris, and a red horn.
- The upper bill is longer than the lower one. Its tip curves downwards over the lower bill.
- The bird's head is dark brown. The head is covered with feathers of a finer texture than the ones on most of the body.
- The head is small in relation to the bulky body. The neck is extensible.
- The upper part of the body is black and has an attractive blue or green sheen.
- The chest and upper belly are white with black flecks.
- The lower belly is light brown.
- The tail is long and black and has a horizontal white band.
- The legs and feet are dark pink to light red.
- On some birds, a small, red dewlap can be seen under the chin.
Males and female horned guans look the same. They can be distinguished by the sounds that they make, as described in the quote below. A vocalizing bird is shown in the video below the quote.
Females produce more guttural types of calls than the deep booming vocalizations of the males. Other sounds include bill-clacking, snorts and clicking. Sounds help identify the sex of this species.— The Dallas World Aquarium
Formation and Structure of the Horn
The horn extends from an unfeathered location on the top of the skull. Its surface is covered with skin. The Saint Louis Zoo has raised two horned guan chicks. According to a photo on their website, a chick's head is at first covered with feathers. The zoo says that the horn starts to form when a chick is about three months old. Two small bumps appear on the head of a chick. The bumps gradually twist together as they grow and eventually form the typical, unfeathered horn of the animal. The mature horn is about two inches long.
According to the last reference below, the bird's horn is an integumentary outgrowth. The integument is the protective outer layer of an animal and consists of skin plus hair, feathers, scales, and nails or claws. The guan's horn may contain a small core of bone that is an extension of the skull, but most of its structure is composed of keratin. The function of the horn may be to attract a mate.
Daily Life of the Bird
The horned guan lives in the high-elevation cloud forests of southeastern Mexico and Guatemala. It appears to spend most of its life in the trees, where it feeds, preens, and sleeps, but it comes to the ground at times. It's usually seen on its own. It does fly, but it's not a very strong flier. A horned guan is shown taking to the air in the video below, though unfortunately the video ends after the bird has taken off.
The guan eats mostly fruit, leaves, and flowers. It also eats some animals, including insects and small vertebrates. When the environment is dry, the bird leaves the trees once a day in order to bathe in the dust on the ground. Many other bird species dust bathe. It's thought that the activity helps to remove parasites from the skin and keeps the feathers in good shape. In some species, the dust baths have been found to control the amount of oil on the feathers and keep the substance at the optimum level.
The male mates with several females in a season. Dust-bathing is part of the courtship ritual. The nest is usually created in the trees. Some researchers have discovered nests on the ground, however. There may well be aspects of the bird's life that haven't yet been discovered. It's still a slightly mysterious animal.
The female produces two eggs per clutch. She incubates them for around thirty-six days. Unlike the case for the rhinoceros hornbill, only the female cares for the hatched youngsters.
LC: Least Concern
NT: Near Threatened
CR: Critically Endangered
EW: Extinct in the Wild
Population Status of the Horned Guan
According to the IUCN, the horned guan is endangered. The status is based on a 2016 assessment. The organization says that the bird's population is decreasing and that only 600 to 1700 adults exist. The problem is mostly due to human actions. The upland forests where the bird lives are being destroyed as coffee plantations move up the mountains. The forests are also being destroyed for logging purposes and to create land for various forms of agriculture. New roads are being built, which makes it easier for humans to enter and modify the forest. In addition, the birds are hunted for their flesh.
The Future for the Birds and Other Wildlife
Nature has created some impressive animals. In many cases, humans are causing or contributing to the decrease in the populations of animal species, as in the two birds discussed in this article. Creating conservation plans is an excellent action, but the plans must be put into action in order the protect animals that are in trouble. Satisfying the needs of humans in a particular area and the needs of the wildlife that lives there is sometimes tricky. It's a problem that we need to resolve.
- Rhinoceros hornbill information from the National Aviary
- Facts about Buceros rhinoceros from the Dallas World Aquarium
- More information about the bird from Zoo New England
- The rhinoceros hornbill entry on the IUCN Red List
- Facts about the horned guan from the Saint Louis Zoo
- Information about the guan from the Dallas World Aquarium
- Horned guan sound recordings from Dibird.vom
- Oreophasis derbianus entry on the IUCN Red List
- Chick births and bird facts (including information about the rhinoceros hornbill and the horned guan) from the Saint Louis Zoo
- Integumentary morphology of modern birds from Integrative and Comparative Biology, Oxford Academic Press
© 2020 Linda Crampton