Double hornbill
| Double hornbill | ||||||||||
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Hornbill ( Buceros bicornis ) |
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| Scientific name | ||||||||||
| Buceros bicornis | ||||||||||
| Linnaeus , 1758 |
The double hornbill ( Buceros bicornis ) is a species of bird in the hornbill family that is widespread in South Asia. It can reach a body length of more than a meter and is one of the largest forest-dwelling birds. Like all hornbills, it is a cave breeder. The female spends the breeding season, which lasts up to four months, in a tree hollow that is walled up except for a narrow crack. During the breeding season, they and later the young birds are provided with food by the male.
The population of the double hornbill is classified as near threatened .
Appearance
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Double hornbills reach a body length of 96 to 105 centimeters. The male's beak is between 29 and 34 centimeters long. In females, this is slightly smaller and reaches a length between 24.5 and 29.5 centimeters.
The horn on the beak, which is formed by both sexes, is very large. The largest horn measured to date was 19.2 inches long, 10.6 inches wide and 5.6 inches high. The horn consists of loose bone framework and is light in weight. It probably has a function as a sound box for the calls of the double hornbill.
The wing span is 162 centimeters. The weight of the males is between 2.6 and 3.4 kilograms. Females weigh between 2.1 and 3.35 kilograms. The sexual dimorphism is weak. The distinguishing feature is on the one hand the size of the birds and on the other hand the color of the iris . In the male , the iris is red-brown in color, in the female it is white.
Characteristics of the male
Males are slightly larger than the females . They have a white crown, neck and front chest. The cheeks, the chin, the back and the rear chest are black. Like the small wing covers, the back has a metallic sheen. The thighs, the belly and the upper tail-coverts as well as the under-tail coverts are white. The wings of the hand and arm as well as the feathers of the large and middle wing-covers have broad white tips. These form a wide white band on the wings. Similar to the breast and neck plumage, these plumage areas often appear yellowish. This is due to the rump fat with which the double hornbill cares for its plumage.
The tail is white with a wide black transverse band across the middle. The beak is bright yellow and turns orange to red towards the tip. A black line runs along the horn attachment and the beak sheaths are also black. The bare skin around the long, labeled eye is black. The eyes are red, the legs and feet are olive green.
Features of the female and young birds
The female has a body plumage similar to that of the male. The horn, however, is yellow to orange with no black coloring. The bare skin around the eye is red, from which the black eyelids stand out. The eyes are white.
Fledglings also have body plumage that corresponds to that of adult birds. With them, however, the beak is even smaller, the beak horn is barely developed. The bare skin around the eye is flesh-colored to pink, the beak is cream-colored, the eyes are pale blue-gray. The legs and feet are greenish-yellow.
In the subadult double hornbills, the beak horn begins to develop from the sixth month of life. The development extends over several years of life and is usually not completed until the age of five. Males don't have red eyes until they are three years old. The color changes from gray to brown and maroon. The bare skin around the eye is gray in the subadult males before it turns black.
Possible confusion
The rhinoceros bird also occurs in the distribution area of the double hornbill . He has a similar height. However, the beak is orange and has a conspicuously upwardly curved horn. He also has a slightly different body plumage. The white plumage on the wings, on the neck and on the crown is missing.
Subspecies
It is controversial whether subspecies can be distinguished for the double hornbill. Alan Kemp assumes in his monograph on hornbills that the size differences that can be determined between the populations between mainland Asia and that of the Malay Peninsula and Sumatra are differences typical of Kline . He therefore does not differentiate between subspecies.
If subspecies are distinguished, they are usually distinguished as follows;
- Siamese hornbill ( Buceros bicornis bicornis ), Linnaeus, 1758 - Thailand
- Homrai hornbill ( Buceros bicornis homrai ), Hodgson, 1832 - India and Southeast Asia
distribution and habitat
The large area of distribution of the double hornbill extends from India through southern China to Sumatra.
In India the range is disjoint . An isolated population lives in the Western Ghats , a mountain range along the west coast of India. However, the main area of distribution in India is the foothills of the Himalayas from Uttar Pradesh to Assam. The distribution area also extends over the south of Nepal and the north of Bangladesh. They are also found in Myanmar and on some densely forested islands of the Mergui Archipelago in the northern Andaman Sea on the west coast of Myanmar in the Indian Ocean . In China, the double hornbill occurs in the west (in Yingjiang ) and south (in Xishuangbanna ) of Yunnan . They are also represented in Vietnam, Laos, Cambodia and Thailand. The Malay Peninsula is also part of their distribution area, where they also occur on islands near the coast. An isolated population also lives on Sumatra.
The double hornbill colonizes evergreen moist primary forests. It is particularly common in forests between 600 and 1000 meters above sea level. In the foothills of the Himalayas and in northern Thailand, however, it can still be found at 2000 meters. It is also found in forests where selective logging has taken place. However, it is not as common there as the smaller hornbill species. Where its range overlaps with the rhinoceros bird belonging to the same genus , the double hornbill is more likely to be found in the higher elevations.
In regions of its distribution area in which there are large contiguous forests, it is quite common. Historically, it has also been a rare bird in more fragmented forest areas such as the Western Ghats .
Way of life
Use of the living space
Double-horned birds live in pairs, in small family groups, but also occasionally in flocks that can contain up to 40 individuals during the monsoon season . Troops often consist of not yet sexually mature individuals who usually roam very large areas for food. However, up to 200 individuals can gather in abundant fruit-bearing trees.
Pairs are loyal to their location and have a breeding area. However, they roam a large area in search of food. During their forays they often follow regular routes. Occasionally they spend a whole day in a single, abundantly fruit-bearing tree. The foraging area they use is an average of 3.7 square kilometers for males during the breeding season - when they have to regularly return to the nest hole to feed the female and later the young birds. Non-breeding males roam feeding grounds with an average size of 14.7 square kilometers. One family group in Thailand was found to roam an area of 608 square kilometers.
Double hornbills often spend the night together in resting trees, to which they keep coming back. They approach these resting trees at dusk, usually using the same route. They use the top branches as a resting place. Usually there are no more than three or four birds in a single tree, larger clusters are spread over several trees. At dawn they leave these resting places again.
Feel-good behavior
Double hornbills bathe in the damp foliage of the treetops and then sit in the branches with their wings open to dry themselves again. They take sunbaths with outstretched wings and spread tail feathers. To cool off, they open their beak and keep their wings slightly raised.
They clean their plumage several times in the morning and apply the yellowish rump oil that turns the white plumage on the neck and chest yellow. In the course of the day this yellowing subsides as the oil rubs off the plumage.
You sleep in a position that is typical for hornbills: the head sinks far back on the shoulders. In this resting position, the beak points slightly upwards.
food
Double hornbills mainly find their food in tree tops. While eating, they hop through the branches with short sideways movements. They also occasionally come to the ground to pick up fallen fruit.
They feed primarily on pulp , especially figs . Double hornbills, which have been studied more closely in Thailand, ate fruit from 26 different tree species. In addition to fig trees, etc. a. Elaeocarpus , Cinnamomum , Litsea , Aglaia , cherry myrtle and pepper trees . Overall, 57 percent of the diet of the examined individuals fell on figs, 29 percent on other fruits and 14 percent on animal food. Outside the breeding season, the proportion of animal protein is likely to be lower.
Although double hornbills are predominantly fruit-eaters, they actively hunt for small animals. Part of their hunting behavior is that they tear off tree bark and look for insects there. They mainly eat insects, including beetles, wasps, grasshoppers, crickets, cockroaches and caterpillars. Crabs, snails and earthworms are also part of their food spectrum. Smaller vertebrates are also eaten, including lizards, frogs, geckos, snakes, bats, and various squirrels . Smaller bird species and their eggs and nestlings are also eaten by the double hornbill. The birds captured included green-bearded birds , goat milkers , flag drongo , Hindu collar owls and jungle pygmy owls , eggs and nestlings of bulbuls and pigeons .
Due to the high water content of their food , hornbills do not need to ingest any additional liquid.
Reproduction
Double hornbills are monogamous birds that breed in tree hollows. They defend a breeding area of about 100 meters radius around this tree hole. Intruders into this area are later driven away even if there is no attempt at breeding.
Behavior before the start of the actual breeding season
Calls from the males can be heard especially at the beginning of the breeding season. There are also fights between males in which the beak and beak horn are used. There is also a report on gatherings of mostly already mated double hornbills, in which the birds beat their beaks against branches and food components are presented to the partner bird. The aggression behaviors that are shown include jumping up and down on a branch and making rapid sideways movements with the beak. How exactly double hornbills choose their partner bird is not known.
The male courtship feeding of the female is one of the more frequently observed behaviors before the start of the breeding season. This feeding takes place near the nest.
Breeding cave
The tree hollows that double horned birds use for their breeding business are usually between 8 and 25 meters above the ground. Caves with a long vertical slot are preferred. Dead trees are also used, but still living trees are more typical. They are often found near fruit-bearing fig trees. Of 25 nests found in Thailand, 20 were in dense forest. The next nest of a double hornbill was between 200 meters and 2.3 kilometers away with an average distance of around one kilometer. Nests of other hornbill species were sometimes only 30 meters from the nesting hole of the double hornbill. In the breeding caves examined in more detail in India, the natural entrances were 40 centimeters high and 14 centimeters wide before being walled up by the hornbills. Nesting caves are used several times even in cases in which predators robbed the nest.
Both parent birds are involved in walling up the nest cavity entrance to the breeding cavity. In this they differ from a number of hornbills, in which only the female walled up the nesting cavity. The involvement of the male in these species is maximally limited to bringing in materials that the female uses to close the nest cavity. In the case of the double hornbill, it is also the male who brings the material. He often swallows the ingredients and then chokes them out again at the nest entrance. The male hornbill takes part in closing the cave from outside. The female works from inside the cave. A mixture of food components, wood parts and bark is used.
After the breeding cave has been walled up, only a narrow slot remains open. The male feeds the female and later the young bird (s) through this narrow slot.
Breeding season
The entire breeding season lasts between 113 and 140 days. Of this, one to four days are accounted for by the time the female already spends in the brood cavity but has not yet started laying eggs. The eggs are incubated for 38 to 40 days and the nestling period is 72 to 96 days. The female usually leaves the breeding cave before the young birds, but spends up to four months walled in the breeding cave. In 15 hornbill females observed more closely, the average length of stay in the breeding cave was 121 days. In the case of double hornbills kept in human care that successfully raised young birds, the shortest length of stay in the breeding cave was 77 days and the longest was 124.
The female usually lays 2 eggs , of which usually only one young survives after hatching. A successful rearing of two young birds has only been observed in the case of double hornbills kept in human care.
The male returns to the brood cavity about three to five times a day and brings food. Mostly it is food that he has swallowed and chokes back at the entrance to the nest. It was observed that when he returned to the nest he brought 50 grape-sized fruits to the nest and on another visit 185 pea-sized fruits of laurel plants . Occasionally it carries larger fruits as well as any animal food in its beak to the nest.
After the young birds have fledged after about 16 weeks, the female opens the brood cavity. She is hammering the masonry with her beak . The young birds reach sexual maturity at 4 years of age.
attitude
Double hornbills are occasionally shown in zoological gardens. Because of their behavior, they are dependent on aviaries that are spacious and as high as possible. They were first bred in human care in 1953. There has been a European conservation breeding program for double hornbills since 1996.
literature
- Mark Cocker, David Tipling: Birds and People . Jonathan Cape, London 2013, ISBN 978-0-2240-8174-0 .
- W. Grummt , H. Strehlow (Ed.): Zoo animal keeping birds. Verlag Harri Deutsch, Frankfurt am Main 2009, ISBN 978-3-8171-1636-2 .
- Alan Kemp: The Hornbills - Bucerotiformes . Oxford University Press, Oxford 1995, ISBN 0-19-857729-X .
- Theo Pagel , Bernd Marcordes: Exotic soft-eaters . Eugen Ulmer Verlag, Stuttgart 2011, ISBN 978-3-8001-5192-9 .
Web links
- More photos of the double hornbill
- Buceros bicornis in the endangered Red List species the IUCN 2015 Posted by: BirdLife International, 2013. Accessed October 31, 2016th
- Videos, photos and sound recordings on Buceros bicornis in the Internet Bird Collection
Single receipts
- ↑ Cocker, Tipling: Birds and People . P. 326.
- ↑ Buceros bicornis in the endangered Red List species the IUCN 2015 Posted by: BirdLife International, 2013. Accessed October 31, 2016th
- ↑ a b c d Kemp: The Hornbills - Bucerotiformes . P. 179.
- ↑ a b Kemp: The Hornbills - Bucerotiformes . P. 178.
- ↑ a b c d e Kemp: The Hornbills - Bucerotiformes . P. 180.
- ↑ a b c d e f Kemp: The Hornbills - Bucerotiformes . P. 182.
- ↑ a b c d Kemp: The Hornbills - Bucerotiformes . P. 181.
- ↑ a b c d Kemp: The Hornbills - Bucerotiformes . P. 183.
- ↑ Pagel, Marcordes: Exotic soft-eaters . P. 85.
- ↑ EAZA website ( Memento of the original from November 4, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , accessed November 3, 2016
