Hornbills

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Hornbills
Female hornbill with food in its beak

Female hornbill with food in its beak

Systematics
Sub-stem : Vertebrates (vertebrata)
Class : Birds (aves)
Order : Hornbills and hops (Bucerotiformes)
Family : Hornbills
Scientific name
Bucerotidae
Rafinesque , 1815

The hornbills (Bucerotidae), sometimes also called hornbills , are a family of birds that is native to the tropics of Asia and Africa. Hornbills include over 50 species. Four species are threatened with extinction and are listed in Appendix I according to CITES , a further 24 species are listed in Appendix II.

The hornbills were placed in the order of the whackebirds (Coraciiformes), by some authors in the order of the hoppy (Upupiformes), or in a monotypical order Bucerotiformes . Today the hoopoes (Upupidae) and the tree hops ( Phoeniculidae) are also placed in this order, and the hornbills ( Bucorvus ), which were previously considered to be hornbills , were given the status of a family, so that the Bucerotiformes now comprise four families.

All hornbill species are omnivorous. The proportion and importance that animal and vegetable diets have in the diet of a particular species, however, varies from species to species.

The hornbills are all cave breeders. They either use natural tree hollows or (less often) rock hollows. The entrance to the nest cavity is sealed by the female except for a narrow gap. The individual species use different materials. The female often uses her own excrement, pieces of bark and food porridge. In some hornbill species, the male brings material that the female uses. The females spend up to four months in the brood cavity, depending on the species. They and later the young birds are provided with food by the male.

features

The beak and horn of a double hornbill

Hornbills reach body lengths between 30 and 120 centimeters. One of the smallest is the pigeon-sized dwarf toy . The double hornbill , which reaches a body length of more than one meter, and the shield beak with a body length of up to 1.2 meters are among the largest forest-dwelling bird species. According to these differences in size, hornbills weigh between 111 grams and a little more than three kilograms. Males always tend to be slightly larger than the females.

This family is named after the large, mostly curved beak, which, except for the tokos, has a bulging top. In most species of the Toko genus, the horn typical of the rhinoceros bird is reduced to an inconspicuous beak ridge. The "horn" of the other hornbill species is mostly hollow or consists of loose bone tissue, only in the case of the shield beak ( rhinoplax vigil ) it is massive. The horn can get very big. Hornbills have horns measured 19.2 centimeters long, 10.6 centimeters wide and 5.6 centimeters high.

Bare, strikingly colored areas of skin can be found on the head and neck. In all species there is a threatening behavior in which the beak is raised and thus the feathered and often high-contrast colored throat patch is presented. Further characteristics are the elongated body, a long neck and short and wide wings. The long tail has ten tail feathers. In most species there is not only a size difference between females and males, but a sexual dimorphism is also present in the color of the plumage, the beak and the beak attachment. Many species have black and white plumage. In the genera Buceros and Aceros , however, there are species that color their plumage red, orange or yellow with a colored rump secretion, depending on the species. The extent of this change in color varies from person to person.

distribution and habitat

Grautoko , male, South Africa

The species of hornbills are almost equally distributed in southern Asia and sub-Saharan Africa. They are completely absent in the New World, their role there is to a certain extent performed by the toucans . The island of Borneo is one of the regions in which a particularly large number of different hornbill species live.

Some species have very large ranges. These include, for example, the oriental hornbill , which occurs in two subspecies from the foothills of the Indian Himalayas via Nepal and southern China to Indonesia. Some of the African tokos, such as the gray toko or the magpie toko , are also very common. There are also a number of species with very small distribution areas. These species are mainly found among the Asian hornbills. Some of them are limited in their distribution to a few islands. They are particularly affected by habitat changes and accordingly many hornbill species with such small distribution areas are particularly threatened: The Palawan hornbill, for example, is one of the endemics of Palawans , a 450-kilometer and up to 40-kilometer-wide Philippine island that is known for its high degree of biodiversity and Endemism is known. Its stock situation is considered endangered ( vulnerable ). The endangered Sulu hornbill , on the other hand, probably only occurs on the island of Tawi-Tawi , while the Panay hornbill , which is estimated to have only 502 breeding pairs, only breeds on Panay . The forest population on Negros is now so small that he can no longer raise young birds there. The also endangered Narcondam Hornbill is only native to the island of Narkondam .

The habitat of hornbills ranges from the dry savannas of sub-Saharan Africa to the humid, evergreen tropical rainforests of Asia. Of all species, the Monteiro Toko , which occurs in the west of sub-Saharan Africa, inhabits the habitat with the least rainfall. Hornbills living on the savannah make up only a quarter of the hornbill species. Of these, only the wedge-tailed toko occurs in Asia; most of the savannah hornbills belong to species common in Africa.

Food and drinking behavior

Malay hornbill eating female

The long beak, the long, highly mobile neck and the strong, graspable feet allow hornbills to use a wide range of food. The lower and upper bills only meet at the tip, so that hornbill species can use the beak like a pair of tweezers. Hornbills are able to reach for objects with great skill. By throwing their heads up, they then throw the food components into their throats, often after having previously crushed them with their beak sheaths. Their long beak and their skill in using it also allow them to eat poisonous animals such as scorpions.

Hornbills are omnivores. Fruits and insects as well as smaller vertebrates, however, have a different share in the food spectrum for each species. Most species cover most of their nutritional needs with fruits. Different species of figs play a particularly important role in the diet of many species.

Animal diet

Male blanket toko with a captured beetle
Males the Malabarhornvogels during feeding

Hornbills, which live mainly on animal protein, are found predominantly in the African savannah. The feeding habits of some of these hornbill species have been studied more closely: They eat small vertebrates and insects from at least 100 different genera. Hornbill species, in which animal food predominates in the food spectrum, tend to be resident birds and defend a territory. They are also less frequently associated with their partner bird or other individuals of the same species while foraging for food. The way in which the hornbills, which mainly eat animal food, find their prey, in turn determines their territory size. The gray tooko, which populates the savannah with its sparsely populated trees and finds its prey mainly in the treetops, needs a territory three to four times larger than the red-billed tooko that occurs in the same habitat and searches for its food on the ground.

The Tokos are the species in which animal food dominates: Red -beaked Toko and Monteiro-Toko are the two species that almost never eat fruit. For all other hornbill species, a diet with fruits, berries and seeds predominates. Even the species that feed mainly on plants spend a lot of time hunting and are very skilled at acquiring animal food. A tame oriental hornbill has been observed to be able to catch flying swallows and bronze males . Even long-crested hornbills have been spotted, she slowly flying swiftlet caught in flight. The silver cheek hornbill , which can reach a body length of 70 centimeters, is even able to catch red-nosed green pigeons , a type of pigeon belonging to the fruit pigeon, which with a body length of 30 centimeters corresponds to the size of a small city ​​pigeon . Silver cheek hornbills live mainly on fruits, but they show an extremely aggressive hunting behavior. For example, they jump up and down on branches to scare off prey. Smaller groups of this hornbill species also attack resting fruit bats together .

Oriental hornbills have been observed successfully catching fish in shallow ponds. Other vertebrates that eat oriental hornbills include nestlings of various smaller bird species, some of which they also get from nesting holes, as well as smaller adult birds as well as bats, lizards and snakes. They also eat scorpions and snails, beetles, crickets, cockroaches, moths, butterflies, grasshoppers and termites and thus cover a spectrum of prey that is found in a similar composition in many hornbill species.

Protocol cooperation

Some of the hornbill species that predominate on animal diets follow other species that startle insects as they forage. These can be wandering ants, groups of monkeys, groups of other bird species or squirrels. Two types of hornbills have behaviors towards another animal species that can already be described as protocooperation : the blanket toko and the eastern yellow-billed toko cooperate with Helogale parvula undulata , a subspecies of the southern mongoose . The two Toko species catch the insects (especially grasshoppers) that these mongooses , which live in groups, scare off when they search for food. The dwarf mongooses benefit from this protocooperation because both tokos warn of predators from the air. The dwarf mongooses wait for the toko to begin their prey. The two toko species also show specific behaviors to indicate to the dwarf mongooses that they are willing to cooperate.

Vegetable food

Malabar gray coco eating

The fruits eaten by hornbills fall into three categories:

  • Fruits that are high in carbohydrates and liquids, such as the various wild fruits that play a major role in the diet of numerous hornbill species
  • Capsule and stone fruits that are rich in fats or lipids
  • thick-skinned fruits that contain a lot of liquid.

In principle, fruits are only eaten when they are fully ripe. The fruits then have a low phenol content and are high in sugar. Most of the fruits that hornbills eat are red, black, or purple when ripe - but this is true for most frugivorous bird species. Basically, hornbills prefer those fruits that have an oily, fleshy aril around the seeds. In some of the forest-dwelling Asian hornbill species, consumption of fruits from 30 to 35 different plant species was counted during the breeding season. However, this represents only a fraction of the available fruits. In the rain-humid tropical forests on Borneo, which are particularly rich in species, 900 different plant species bear fruit. However, only 128 species are definitely used by the hornbills, with the fruits of another 144 plant species it is possible that they are eaten by the hornbills.

Figs play a huge role in the diet because they are found in different species in numerous forest forms. They are often very common tree species in the respective regions that regularly bear numerous fruits. The individual trees also ripen at different times. Some of the fig species are also very rich in protein.

In addition to figs, the fruits of ebony trees and balsam trees also play a larger role in many species . Stone fruits and capsule fruits are produced by a wider range of plants. Compared to fig species, however, the individual trees bear a smaller number of fruits. Hard skin or a stone that is large in relation to the pulp make them more difficult to harvest compared to figs. Many of these plant species only ripen at certain times of the year, so that a rich supply of this food is only available for a few weeks.

Special nutritional ingredients

Wedge-tailed Toko eating

Hornbills repeatedly include certain food components in their diet that are only eaten occasionally. This includes eating empty snail shells in the weeks before eggs are laid. These snail shells may serve as a source of calcium and aid in egg shell formation. In addition, hornbills regularly eat flowers, which are rich in certain proteins due to their pollen, as well as saplings and buds, which contain a lot of sugar, and mushrooms, which are rich in vitamins.

Centipedes and sticky fruits are often ingested, but especially not eaten during the breeding season. They are chewed up by various hornbill species to make the food that is used to seal the breeding cavity.

Drinking behavior

The uptake of water does not appear to be necessary for any of the hornbill species, although there are species of the Asiatic throat pouch hornbills and the magpie hornbills that go into the water because they are believed to catch fish or crabs there. Drinking has generally only been observed in four species so far and this was noted as unusual behavior in each of these species. It has only been observed once in the case of the Red-billed Toko and the Malay Hornbill in birds kept in human care. In the case of the black-helmet hornbill and the eastern yellow-billed coconut , there were observations in wild birds. In principle, hornbills seem to cover their fluid requirements with their food and this also seems to be the reason why figs, for example, play a major role in the food spectrum of very many species.

Reproduction

Wedge-tailed toko ( Ocyceros birostris ) at the nest cavity
A male hornbill at the nest hole

All hornbills are cave breeders. Hornbills very rarely use burrows in the earth for their breeding business. Occasionally they also use rock caves. Most hornbills, however, breed in natural tree hollows. These tree hollows are usually located high above the ground. Hornbills often use suitable tree hollows for several years. They hardly undertake any construction activities on the actual nesting hole. Only loose wood in the cave and occasionally the bark at the entrance are removed.

All species have in common that the female walled herself up in the breeding cavity except for a narrow gap. As a result, the offspring are largely protected from nest predators, but the male is solely responsible for food supply for a long time. In the silver cheek hornbill, in which the female stays in the brood cavity for up to 138 days, the male brings around 24,000 fruits to the brood cavity. It also flies to the breeding cave about 1,600 times. On average, there are 360 ​​grams of fruit a day that the male brings in the throat or beak.

As a rule, the male is not involved, or only to a small extent, in closing the nest cavity. Among the exceptions to this are the trumpeter hornbill , the gray-cheeked hornbill and the silver -cheeked hornbill . The male swallows lumps of clay and chokes them out again in the form of small balls of clay. The female then builds this clay when sealing the brood cavity. When a trumpeter hornbird's nesting cave was examined more closely, the material used weighed 1.47 kilograms. With most hornbill species, however, the female does not use clay to wall up the breeding cave, but her own excrement and food pulp. In the species in which the female leaves the nest hole before the young birds, the young birds independently seal the entrance to the nest cavity. In many species, the female does not begin to lay eggs immediately after the brood cavity is closed, but only after a period of four to six days.

The female keeps the brood cavity clean by excreting through the narrow gap. The young birds also show this behavior as soon as they have reached a sufficient size to reach the nest cavity. In a number of species, the female leaves the breeding cave before the young birds fled and provides the offspring with food together with the male. In other species, the female remains in the breeding cavity until the offspring have fledged. In these species, the female spends up to four months in the brood cavity. The offspring are capable of flight when they leave the nest box. He does not return to the brood cavity.

The female usually moults during brood. In some species, such as the Tokos, the female moults the large plumage at the same time and is therefore temporarily unable to fly. In other species the large plumage is molted one after the other, the females retain their ability to fly.

The large species of hornbills lay clutches of one and two eggs. Usually only one young bird grows up. In the small hornbill species, the clutch can contain up to five eggs. The eggs are incubated between 23 and 42 days. This is followed by a nestling period of several weeks in the breeding cave.

Genera and species

Southern Yellow Beak Toko
Hornbill ( Aceros cassidix ) in the Walsrode World Bird Park
Oriental hornbill , male
Rhinoceros bird
( Buceros rhinoceros )
Silver cheek hornbill ( Bycanistes brevis )
Fire hornbill ( Buceros hydrocorax ) in the Walsrode World Bird Park
Mindanaohornvogel , Walsrode World Bird Park
Hornbill
Long-crested hornbill , female

literature

Web links

Commons : Hornbills  - Album with pictures, videos and audio files

Single receipts

  1. ↑ Pagel, Marcordes: Exotic soft-eaters . P. 82.
  2. ↑ Kemp: The Hornbills - Bucerotiformes . P. 148.
  3. ↑ Cocker, Tipling: Birds and People . P. 326.
  4. ↑ Kemp: The Hornbills - Bucerotiformes . P. 6.
  5. ↑ W. Grummt, H. Strehlow (Ed.): Zoo animal keeping birds . P. 537
  6. ↑ Kemp: The Hornbills - Bucerotiformes . P. 179.
  7. ↑ a b Kemp: The Hornbills - Bucerotiformes . P. 28.
  8. ↑ a b Kemp: The Hornbills - Bucerotiformes . P. 5.
  9. ↑ a b c d e f g h Kemp: The Hornbills - Bucerotiformes . P. 42.
  10. ↑ Anthracoceros marchei in the endangered Red List species the IUCN 2012. Posted by: BirdLife International, 2012. Accessed October 29, 2016th
  11. ↑ Rhabdotorrhinus waldeni in the endangered Red List species the IUCN 2016 Posted by: BirdLife International, 2016. Accessed December 9, 2016th
  12. ↑ Anthracoceros montani in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed October 31, 2016th
  13. ↑ Kemp: The Hornbills - Bucerotiformes . P. 129.
  14. ↑ Kemp: The Hornbills - Bucerotiformes . P. 37.
  15. ↑ a b Kemp: The Hornbills - Bucerotiformes . P. 40.
  16. ↑ Kemp: The Hornbills - Bucerotiformes . P. 38.
  17. ↑ Kemp: The Hornbills - Bucerotiformes . P. 212.
  18. ↑ David Gibbs, Eustace Barnes and John Cox: Pigeons and Doves - A Guide to the Pigeons and Doves of the World . Pica Press, Sussex 2001, ISBN 90-74345-26-3 , p. 443
  19. ↑ a b c Kemp: The Hornbills - Bucerotiformes . P. 259.
  20. ↑ Kemp: The Hornbills - Bucerotiformes . P. 167 and p. 168.
  21. ^ Alan Kemp: The Hornbills - Bucerotiformes . Oxford University Press, Oxford 1995, ISBN 0-19-857729-X . P. 141 and P. 143
  22. ↑ a b c Kemp: The Hornbills - Bucerotiformes . P. 41.
  23. ↑ a b Kemp: The Hornbills - Bucerotiformes . P. 39.
  24. ↑ Kemp: The Hornbills - Bucerotiformes . P. 259 and p. 260.
  25. ↑ Kemp: The Hornbills - Bucerotiformes . P. 248.
  26. ↑ Kemp: The Hornbills - Bucerotiformes . P. 220.