Introduction
Hornbill is a bird species and falls under any of the sixty species of the Old-World tropical birds of order Coraciiformes. The scientific name of hornbill is ‘Bucerotidae’, which means ‘cow horn’ in Greek. They are specifically noted for their characteristic feature of a bony casque which is crowned on their prominent bill. This is found only in a few species. They are found to have a large head that is held by a thin neck. Their wings are broad and their tails are long. The plumage is usually black or brown, having bold white markings. The size of hornbills ranges approximately from 16 inches (i.e., 40 cm) to 63 inches (i.e., 160 cm). The Tockus species is generally smaller in size than that of the great hornbills. Several hornbill species like the Rhinoceros hornbills have the preen gland near the base of their tail. When the beak and the casque rub against this gland, an oily, reddish-orange fluid is secreted which gives the beak and casque a bright, reddish tone.
Classification
Kingdom : Animalia
Phylum : Chordata
Subphylum : Vertebrata
Class : Aves
Order : Coraciiformes
Suborder : Bucerotes
Family : Hornbills (Bucerotidae)
Number of genera, species - 14 genera; 54 species.
Habitat - Forest, woodlands, and savanna.
Conservation status - Endangered: 2 species; Critically Endangered: 2 species; Vulnerable: 5 species; Near Threatened: 12 species.
Physical characteristics
Hornbills are among the most flamboyant birds of their habitat. The oversized, slightly decurved bills topped by sometimes outlandish casques shaped as bumps, ridges, or horns make hornbills an unforgettable component of any landscape.
Hornbills vary tremendously in size and shape, starting with the large, long-legged southern ground-hornbill (Bucorvus leadbeateri) weighing up to 13.2 lb (6 kg), and going down to the 0.26 lb (120 g) red-billed dwarf hornbill (Tockus camurus).
Males are always larger and stouter than females but the greatest dimorphism often occurs in bill length with males having up to 30% longer bills. Horn-bill plumage is described as "drab," lacking the brilliant colors of relatives such as the kingfishers (Alcedinidae) and rollers (Coraciidae).
However, the bold black-and-white patterns of many forest hornbills and the delicate gray pied patterns of many Tockus species are far from dull. Add in bills and casques of brilliant orange, yellow-gold, deep crimson, or shiny black, and patches of bare skin around the eyes and throat in a kaleidoscope of garish hues, and you have a colorful group of birds.
Plumage color and size and shape of the casque identify the age and sex of an individual. Newly fledged hornbills have underdeveloped casques and small bills, but after the first year of life, appearances converge on that of their adult counterparts.
In species where sexes differ in color as adults, determining the gender of the young can be difficult. For example, in almost all Aceros, Rhyticeros, Penelopides, and Tockus species, the young, regardless of their sex, resemble their fathers for the first year of life.
The opposite is true for the Bycanistes and Ceratogymna who resemble the adult female. Young of the northern ground-hornbill (Bucorvus abyssinicus) and a few Tockus species show plumage true to their sex while chicks of the rufous hornbill (Buceros hydrocorax) are radically different from both parents.
Numerous authors have described the noise produced by flying hornbills as that of an approaching train. This incredible "whooshing," produced in different pitches depending on the species' size, is a result of wing structure.
Because horn-bills lack the small feathers that normally cover the shafts of the primary and second flight feathers, each powerful stroke of the wing allows air to pass through and vibrate the large feathers.
The most outstanding feature, and the one from which hornbills acquire their common name, is the casque on the top of the bill. Casques vary from the mere ridge of the redbilled hornbill (Tockus erythrorhynchus) to the wash-board bumps of the wreathed hornbill (Rhyticeros undulatus) and the elaborate banana of the rhinoceros hornbill (Buceros rhinoceros).
The function of casques, which may take up to six years to develop, is the topic of many debates. It is possible that casques provide structural support for a long bill. Casques may also serve an acoustic function by helping amplify a horn-bill's call. Additionally, casques may be attractive to the opposite sex.
The helmeted hornbill uses its casque in bizarre, aerial displays where individuals of either sex collide in midair, casque-to-casque. The head-butting competitions always occur near fruiting fig trees (Ficus spp.).
Although Gustav Schneider once reported that helmeted hornbills perform this comical ritual when they are intoxicated on fermented figs, observations from Sumatra indicate that this acrobatic act may be in defense of clumped food resources.
Behavior
Hornbills generally wake at dawn, preen their feathers, then begin their search for food. Normally, hornbills move about in pairs, but some species are found in family groups of three to 20 individuals. Some hornbills gather in large flocks around clumped food resources.
The Sulawesi redknobbed hornbill is occasionally seen in groups of more than 100 individuals at large fruiting figs. In Thailand, wreathed hornbills roost in flocks of over 1,000 individuals. The plain-pouched hornbill (Aceros subruficollis) takes the record for the largest aggregations; over 2,400 individuals were counted in Malaysia in 1998 traveling to roost.
Roosts may serve as "information centers" where individual birds can reduce foraging time by following a knowledgeable, long-term resident. As Alan Kemp summarizes, these massive gatherings are "wonderfully noisy and visually stunning, and must surely rate among the foremost spectacles of the bird world."
Hornbills are believed to be monogamous. The only research on the faithfulness of hornbills failed to find evidence of extra-pair paternity in Monteiro's hornbill (Tockus monteiri), boosting confidence in their monogamous behavior.
Monogamy may have many variations on the theme. Among cooperative social groups, there is generally one monogamous breeding pair and a number of offspring who become "helpers" during the nesting season, delivering morsels to their mother and siblings and defending a mutual territory.
Cooperative breeding occurs more often in hornbills than any other bird family, and may characterize up to one-third of all hornbill species.
Many hornbills range widely but none of these movements is considered migratory. Most hornbills are sedentary and many are territorial. The majority of Tockus and small-bodied forest hornbills are territorial throughout the year.
Larger hornbills such as the Aceros and Rhyticeros that rely on scattered fruit resources, may range over 21 mi2 (58 km2) and only defend temporary territories around nest sites.
Hornbills communicate through a wide range of spectacular calls and each species can be identified by its vocalizations. Loud calls announce territories, or in the non-territorial species, aid in maintaining contact.
Territorial ground-hornbills "boom" when their boundaries are invaded and non-territorial wreathed hornbills bark like dogs while coordinating flocks. While calls are important in dense forest habitats, visual displays are more prevalent in open grasslands.
For example, the Hemprich's hornbill (Tockus hemprichii) has an elaborate territorial display that resembles the mechanical movements of a wind-up toy; the bill is pointed skyward, while the bird whistles, and lifts and fans its tail over its back.
Feeding ecology and diet
Hornbill diets span the spectrum from animals to fruits and seeds but most are omnivorous, mixing meat and fruit in their meals.
Among Tockus, diets tend more toward insects, scorpions, lizards, snakes, and small mammals, while Ocyceros and tarictic diets include more fruit. Omnivory is the rule among the territorial, group-living hornbills.
Because animal prey often occurs at low density and is available year-round, hornbills may develop defendable territories in which dietary needs for the pair or group are satisfied.
Additionally, these species maximize exploitation of their territories by using abundant but ephemeral fruit resources as they become available. The availability of fruit resources within a habitat may determine the degree of omnivory observed.
Heavy reliance on fruits requires that hornbills have large home ranges, and may affect reproductive rates. Fruit diets combined with large home ranges have important consequences for forest ecology.
As hornbills travel, they disperse seeds of the fruits they relish, playing a role in regenerating the forests in which they live.
Reproductive biology
Hornbill reproduction tends to coincide with rainfall and increased food supply. In seasonal African savannas, Tockus species begin courtship and reproduction with the rains, when invertebrates and fruits are plentiful.
The opposite occurs on Sulawesi where lack of rainfall stimulates reproduction in the Sulawesi red-knobbed hornbill, so the burst in fruit supply occurs immediately after fledging.
In aseasonal Bornean rain-forests, reproduction appears to be supra annual, tied to highly cyclical peaks in food supply.
Breeding in these populations may be controlled by the rate at which pairs regain condition between reproductive cycles. In fig-rich forests of North Sulawesi, hornbills breed every year, usually returning to the same nest tree.
The hornbill's unique nesting behavior is the feature that has most fascinated students of nature. All hornbills are hole-nesters, preferring natural cavities in trees or rock crevices.
Unlike any other group of birds, the female hornbill seals the entrance to her nest cavity, leaving only a narrow slit through which she, and later her chicks, receive food from her mate.
In most species, the male ferries mud to the female who then works for several days to seal the cavity entrance. Where mud is a rare commodity, the female uses her own feces as building material.
Nest sealing is believed to have evolved as a form of predator defense, for protection against other intruding hornbills, and to enforce male fidelity. Nest sealing has been described as an example of male chauvinism in which the male cloisters his female, forcing her to depend on him for survival.
In reality, the female incarcerates herself and later frees herself, forcing the male to provide for her and their offspring. Because the male is busy provisioning his family, he is incapable of maintaining two nests, and the female can be sure of his complete attention.
The onset of breeding begins with courtship. When in flight, courting pairs act as though they are attached by an invisible rubber band, reacting swiftly to each other's movements.
They perch in cozy proximity, engage in mutual preening, and exchange food gifts as a demonstration of their ardor.
Other clues of the onset of breeding include the intensification in color of the exposed fleshy areas around the face and throat, reflecting hormonal changes. Nest inspection increases in frequency until copulation occurs and the female enters the nest cavity.
The number of eggs, their size, and the length of incubation are all correlated with body size. Clutch size ranges from two to three eggs in large hornbills and up to eight for smaller hornbills.
Incubation runs from 23-49 days in small and large species, respectively. Eggs hatch in intervals and the emerging chicks are naked and translucent pink with closed eyes. Feather growth begins within a few days and as chicks develop, the skin blackens and begging calls change from feeble cheeps to loud, insistent calls.
The timing of female emergence varies tremendously; some females accompany their chicks from the nests and others leave well before chicks fledge. Research on Monteiro's hornbill suggests that females emerge to ensure survival when their body condition reaches its lowest point.
Male hornbills can be impressive providers. Although many Tockus species carry items to the nest one-by-one, most hornbills collect multiple food items, stuffed into a bulging gullet before delivering a load to the nest. A Sulawesi redknobbed hornbill once delivered 162 fruits in one trip, a load equivalent to nearly 20% of his body weight.
Nesting success is high for those species studied. In southern Africa, chicks fledged from 90–92% of the nests of four Tockus species and in Thailand, 80% of great hornbill nests monitored fledged young. Sulawesi red-knobbed hornbills averaged 80% nesting success over three years, but this figure plummeted to 62% during the 1997 El Niño/ENSO fires. Smaller hornbills fledge up to four chicks, but large hornbills rarely fledge more than one chick per year.
Conclusion
The hornbills are noted by the International Union for Conservation of Nature (IUNC) Red List of Threatened Species so that the majority is not on the verge of getting extinct. Species of hornbills like the bushy-crested hornbill (Anorrhinus galeritus) in South Asia and the crowned hornbill (T. alboterminatus) in southern Africa are extended in huge geographic ranges due to their large populations. However, due to hunting pressure and deforestation, ecologists found that the population of some species is under threat. The IUNC Red List classifies some species to be endangered which include the Narcondam hornbill, the Visayan hornbill (P. panini), a native to Panay Island and its small, neighbour islands, and the Mindoro hornbill (Penelopides mindorensis), which is from Mindoro in the Philippines. Also, the rufous-headed hornbill (Aceros waldeni), also known as Walden’s hornbill, and the Sulu hornbill (Anthracoceros montani) are listed to be critically endangered. Both the helmeted hornbill and the great hornbill are protected due to their casque, which is used as carving material like ivory.
Facts
1.The Rhinoceros Hornbill is the mascot of Sarawak city. But, other hornbills are also found here and for obvious reasons, the nickname ‘the land of hornbills’, is given.
2.Hornbills are the best friends of monkeys as these birds eat up the insects which annoy the monkeys. In return, the hornbills get warning calls from the monkeys if they see any humans.
3.The calls made by hornbills are very loud and distinct. The Indian great hornbills make a roaring sound, the Von der Decken’s hornbills make a clucking sound, and the southern ground hornbills make a resounding bass sound.
4.During the nesting period, the male bird can carry up to sixty fruits in a single go. They also flap their wings on the nest to communicate with the female. The flapping action creates a sound similar to a steam engine.
5.Besides constructing nests, the hornbills use their beaks to climb trees also.
