Vulture raven

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Vulture raven
Vulture raven (Corvus albicollis) on the edge of the Tanzanian nature reserve Ngorongoro

Vulture raven ( Corvus albicollis ) on the edge of the Tanzanian nature reserve Ngorongoro

Systematics
Order : Passerines (Passeriformes)
Subordination : Songbirds (passeri)
Superfamily : Corvoidea
Family : Corvids (Corvidae)
Genre : Ravens and Crows ( Corvus )
Type : Vulture raven
Scientific name
Corvus albicollis
Latham , 1790

The White-necked Raven ( Corvus albicollis ) is an Singvogelart from the family of corvids (Corvidae). The predominantly black bird with a white neck is a large representative of the ravens and crows ( Corvus ) and lives in highlands and cliffs in eastern and southern Africa. Its diet consists of a wide variety of insects and small vertebrates, as well as carrion, human waste and fruits. Vultures usually live in pairs and then stay together all life, but can also form larger flocks with conspecifics and other crows.

The vulture raven is predominantly a rock breeder, but occasionally builds nests in trees. Its breeding season usually begins between August and November, but the start of breeding varies regionally. The chicks hatch after 19 to 26 days and fledge after a further 21 to 28 days. The closest relative of the vulture raven is the arch raven ( Corvus crassirostris ) from the Ethiopian highlands , which is very similar in plumage, body structure and choice of habitat, but is even larger. In the majority of its distribution area it is considered a rather rare bird, in some regions its population is declining. The IUCN nevertheless rates the endangered status of the species as Least Concern (no endangerment).

features

Physique and plumage

With a body length of 50–56 cm, the vulture raven is a very large and stocky raven, which can be recognized primarily by its strong, curved beak and the white collar in the otherwise brown-black plumage. Males of the species are slightly larger than females, but there is no sexual dimorphism in terms of plumage . Male vultures have a wing length of 357–434 mm and a tail length of 170–194 mm. Their beak is 65–70 mm long, while the barrel bone measures 74–80 mm. The wing length of the female is 358-420 mm, its tail has a length of 148-182 mm. The beak is 62–67 mm long, the barrel bone measures 70–77 mm. In both sexes, the beak measures between 30 and 35 mm in depth and has a high, curved beak ridge.

Photo of the head and torso of two vultures
A pair of vultures at the Cincinnati Zoo . The high, curved and furrowed beak, throat plumage and the white collar in the neck plumage are clearly visible.

The head, neck, throat and belly plumage is predominantly black to Van Dyke brown with a purple sheen. The only exceptions are the coal-black feathers around the reins and the plumage around the beak and eyes. The nasal bristles stand out clearly. They are arranged like a fan, slightly curved upwards and cover almost a third of the upper beak. Breast and throat feathers are strongly forked and slightly elongated. The neck and chest plumage is sometimes enclosed by a line of white-lined feathers. The proportion of these feathers in the plumage and their whiteness vary from individual to individual; in some birds there are also completely white feathers below them. At the nape of the neck a wide white collar adjoins the dark brown head plumage. The rest of the plumage is deep coal black and has a slight green tinge. Over time it fades and turns brown, so that it resembles the plumage of the head. Vultures have a dark brown iris as well as black wax skin and black legs. The beak is coal black, its tip ivory colored.

Young birds have softer and more woolly plumage than adult birds. The light line around the neck, which is usually only vaguely present in adult birds, is more pronounced in juvenile birds and forms a white band on the underbust of some individuals. The white collar is often interspersed with black lines or speckles. The beak of the young birds lacks the bright tip, it is uniformly black.

Flight image and gait

Photo of a flying vulture
Vulture raven in flight with characteristic short tail feathers and broad wings

The vulture raven usually circles with slow, flat wing beats. In addition, it is also capable of fast and agile flight maneuvers. Couples in particular show tumbling swoops or rolls or throw sticks at each other in flight. The wings generate whirring and rustling sounds that can be heard from far away. The vulture raven differs from other ravens and crows in its area of ​​distribution mainly by its powerful beak, broad wings and relatively short tail. On the ground the vulture raven moves both hopping and striding. His gait is upright, striding and strutting.

Vocalizations

For a raven species of its size, the vulture raven has a very high-pitched and hoarse voice. It is, for example, higher than that of the Holarctic common raven ( Corvus corax ), which is roughly the same size and which is otherwise acoustically very similar to the vulture raven . Usually he calls with a falsetto- like kroohr-kroohr or kraak-kraak-kraak . The call spectrum also includes deeper, throatier calls such as a rolling krooo , which can sometimes sound like trumpets and also functions as an alarm call, as well as a hoarse haa . The begging call aaa, aaa is similar to that of other Corvus species, but also has the hoarse note of the other vulture raven calls . When it is uttered very forcefully, it sounds like fanatical shouting. When approaching potential partners, the vulture raven lets out a metallic rattling klk-klk-klk-klk-klk , while holding its head down. He is also able to imitate the calls of poultry .

Spreading and migrations

The distribution area of ​​the vulture raven stretches from the region of Lake Victoria and the surrounding mountains to the south along the mountain ranges in the south-east African hinterland to the Cape region .

Topographic map of Africa with the distribution of the vulture raven
The range of the species largely coincides with the mountain ranges in the east and south of Africa

In the outer eastern Congo as well as in the west of Burundi , Rwanda , Tanzania and Uganda , the distribution area largely coincides with the Central African Rift . In Uganda it extends to the north shore of Lake Victoria and from there it arches to the Mount Kenya and Kilimanjaro massifs . From there it follows the East African Rift south to the northern half of Lake Malawi and the neighboring mountains. In northeastern Tanzania it reaches the coast of the Indian Ocean, in the region south of Lake Victoria, however, the vulture raven is largely absent, there are only isolated, island-like occurrences.

On the south-west bank of Lake Malawi, after a small gap, there is a large area of ​​the vulture raven on the mountainous, eastern Great Rim , which is only divided by the river lowlands of the Zambezi and its tributaries. It includes the extreme south of the Democratic Republic of the Congo, the southern border and central region of the Central African Republic , the southern half of Malawi , the western border regions of Mozambique and large parts of Zimbabwe . In the south of Zimbabwe it is interrupted by the Limpopo lowlands , but then continues in the South African Soutpansberg massif and follows the subsequent mountain ranges through South Africa, Swaziland and Lesotho to the Cape of Good Hope . In addition to the mountains, it also includes the south coast of the continent.

The vulture raven is predominantly a resident bird and does not show any migration behavior . He passes but occasionally and places outside the breeding season long distances back in large flocks. It also often leaves its breeding habitats in search of food and migrates down to the surrounding lowlands.

habitat

Photo of a pair of vultures on a cliff
Open and semi-open mountain landscapes like here on Kilimanjaro form the main habitat of the vulture raven.

The vulture raven predominantly inhabits mountainous and rocky landscapes that are either open or have only a sparse tree population, such as cliffs, steep slopes or scree fields. However, apart from closed forests, a wide range of other habitats are also used: grasslands, lake shores, pastureland or highly anthropogenic habitats such as villages, gardens and parks are not unusual habitats for the vulture raven, provided that there are sufficient sources of food and breeding opportunities. However, it is a less pronounced cultural follower than the sympatric tortoiseshell ( Corvus albus ).

The species usually breeds at altitudes of 1000 to 3000 m above sea level. On Kilimanjaro it also occurs up to 5800 m, in the coastal lowlands down to 400 m. When searching for food, however, the vulture raven is not tied to certain altitudes and can also be found in the lowlands.

Way of life

nutrition

Photo of a vulture raven digging its beak in the ground
A vulture pokes between grass and leaves for food. Most of the foraging takes place on the ground.

The vulture raven is omnivorous . Its food spectrum includes carrion as well as live grasshoppers, beetles, snakes, lizards and turtles. In addition, birds up to the size of terns ( Sterna spp.), Mammals, and eggs and nestlings of larger birds such as domestic hens or geese can also be found in its diet . It also kills sick or seriously injured lambs, recycles human waste and consumes fruits, seeds or the nectar of the aloe marlothii .

The vulture raven looks for food mainly on the ground. He holds hard pieces of food with one foot and bites or pounds them with his beak. Like most corvids, he first dips sticky food in water before consuming it. More rarely, he collects insects from the leaves of trees or picks parasites from the fur or skin of large mammals. Turtles such as the African beak- breasted turtle ( Chersina angulata ), which cannot be eaten in the usual way, are dropped by the vulture raven from a great height onto rocks until the hard shell shatters there. Around these so-called “forges” there are often several dozen eroded turtle shells. It hides excess food in tall grass and transports food in both its beak and its claws. He often searches highways for victims of wildlife accidents and is usually the first to come across fresh carcasses. Where the species is not persecuted, it shows no fear of humans and moves freely in their settlements in search of food. Vultures are frequent guests, especially in camps on Kilimanjaro , and have been seen drinking sauce from empty ravioli cans or consuming whole bars of soap.

Social and territorial behavior

Photo of a pair of vultures in a treetop
A pair of vultures hates an intruder

As adult animals, vultures usually live in monogamous , lifelong pair bonds, but also often move in groups. Sleeping and resting places on cliffs are mostly used by several vultures at the same time. These communities usually comprise up to 40, less often several hundred individuals. Flocks of up to 150 birds can gather on the carcasses of large animals, where they fight for carrion together with vultures, kites and tortoiseshell. Even larger accumulations can occur in seasonal swarms of locusts. The largest documented gathering of vulture ravens to date was an estimated 800 individuals.

Pairs of vultures occupy territories and defend them during the breeding season. Wherever there is enough food and nesting facilities, as in cities, the birds apparently tolerate each other and show no signs of intraspecific aggression. In vultures, social play behavior with sticks and stones was observed, but no playful fights, hunts or other forms of play behavior. Mutual plumage care is common among them. In doing so, they lift the feathers of the other person with their bills and search the exposed feather roots for lice and other parasites. In another variant, the birds carefully poke their partner's plumage with their closed or slightly opened beak and show swallowing movements.

Reproduction and breeding

During the mating season , the male brings food to the female, pursues it in mating flights over trees and around rocks and performs flight maneuvers in which it first flies steeply upwards and then falls back down again. The male approaches the female in a stooped position and a rattling call to woo her. Branches and twigs are brought in for the nest and woven into a round bowl. The inside of the nest is covered with algae, grass, hair, wool, feathers or rags. In about 90% of all cases the nest is built on inaccessible rock edges, in the rest of the cases usually in trees.

The start of the breeding season varies from region to region. In the south of the distribution area it tends to start earlier. The main breeding season in South Africa begins in September and lasts until October. In Malawi it lasts from September to November, in Tanzania through October and in Kenya from October to December. In Uganda broods have been observed at different times of the year.

The clutch consists of one to seven, usually four, shiny eggs. They are elongated oval shaped, light green to blue-green in color and covered with brown and olive speckles. The eggs measure 46.0–56.9 × 31.6–35.0 mm and are incubated by the female. The chicks hatch after 19-26 days, have reached about a third of their later size after 7-10 days and show their first feathers. The feces of the young animals are not given over to the edge of the nest, but carried out of the nest or eaten by the mother. The nestlings are fed exclusively by the female, initially by choking up food, and later also by direct feeding. The male often accompanies the female on the flights to the nest, but usually does not feed the nestlings. One brood was fed 30 times in 3.5 hours, the transfer of food taking 0.5-2 s each time. The young birds fledge after 21–28 days, but remain with their parents for a long time, until about one to two months before the next breeding season begins. The average breeding success, depending on the region, is between 2.1 and 2.7 flown out young per brood.

Life expectancy, diseases and causes of mortality

Vultures can reach an age of more than 14 years. Typical parasites of the species are the featherlings Philopterus leptomelas and Brueelia leucocephalus as well as Myrsidea hopkinsi from the animal louse - suborder Amblycera . In Kenya, vultures often die after eating poisoned bait that is laid out there for predators. In South Africa, on the other hand, the species is actively pursued by humans by shooting, purposefully poisoning and trapping it and destroying its nests and clutches.

Taxonomy and systematics

The vulture raven was described very early on . In 1790 John Latham included it in his catalog Index ornithologicus sive Systema ornithologiæ , in which he described the species using a bellows . The specific epithet albicollis means “white neck” in Latin .

The vulture raven belongs to a group of powerful ravens that is found in the east and the extreme south of Africa. Its sister species is the similarly built and colored, but significantly larger and more powerful ore raven ( Corvus crassirostris ), the largest living songbird. According to the molecular clock , the split between the two taxa took place around 2.5 million years ago.

Photo of an ore raven in the Ethiopian highlands
The arch raven ( C. crassirostris ) is the closest relative of the vulture raven

While the vulture raven inhabits the areas along the African Rift Valley to the Cape of Good Hope , the distribution of the ore raven is limited to the highlands of Abyssinia in Ethiopia and Eritrea , which means that the respective areas of distribution do not overlap but are close to one another. The two species are usually placed in a superspecies because they share specific traits such as large, furrowed beak and white neck markings. In the 19th and early 20th centuries, both species were also included in their own genus Corvultur ( Lesson , 1831 ) in order to take into account their highly necrophagic diet and their beak morphology . Formed the basis for this especially Richard Bowdler Sharpe's work Catalog of the Passeriformes, or perching birds, in the collection of the British museum. Coliomorphae from 1877. In it he applied a strongly differentialistic concept to the genus Corvus and divided it into 12 sub-genera, including Corvultur . Only Richard Meinertzhagen turned 1926 against Sharpe's concept by the transitional forms between individual Corvus argued species. Dean Amadon followed Meinertzhagen in 1944 in this view, whereupon vulture and ore raven were again assigned predominantly to the genus Corvus in scientific publications . Both species form the sister clade of the Holarctic ravens and separated from them in the early Pliocene (about 4  mya ). No subspecies are recognized for the vulture raven. 

status

In most of its range, the species is a little more common or locally more common bird, many regions are probably only sparsely populated. In Mozambique, the estimated population is fewer than 100 birds. In South Africa, where it is still persecuted as a pest, the vulture raven was probably more common in the 19th century than it is today, as sightings from Pretoria , Klerksdorp or the Magaliesberg suggest. There is also a decline in the population in Kenya, where vultures often eat poisoned carcasses. Nevertheless, the vulture raven is not considered threatened because, according to Steve Madge and Hilary Burn, local gatherings of several hundred animals suggest a large total population and the species is represented in many nature reserves. Based on this assessment, the IUCN lists it in the Least Concern category (no hazard).

Sources and References

literature

  • Dean Amadon: The Genera of Corvidae and their Relationships. In: American Museum Novitates 1251, January 1944. pp. 1-21.
  • M. Antiqur Rahman Ansari: A Revision of the Brüelia (Mallophaga) Species infesting the Corvidae. Part II. In: Bulletin of the British Museum (Natural History) 5 (4), June 1957. pp. 6-182.
  • Leslie Brown, Emil K. Urban , Kenneth B. Newman (Eds.): The Birds of Africa. Volume 6: Picathartes to Oxpeckers. Academic Press, 2000, ISBN 0121373010 .
  • Josep del Hoyo, Andrew Elliot, David Christie (Eds.): Handbook of the Birds of the World. Volume 14: Bush-shrikes To Old World Sparrows. Lynx Edicions, Barcelona 2009. ISBN 9788496553507
  • Judy Diamond, Alan B. Bond: A Comparative Analysis of Social Play in Birds. In Behavior 140, 2003. pp. 1091-1115. (Online as PDF )
  • Urs N. Glutz von Blotzheim , KM Bauer : Handbook of the birds of Central Europe. Volume 13 / III: Passeriformes. 4th part. AULA-Verlag, Wiesbaden 1993, ISBN 3-89104-460-7 .
  • Derek Goodwin: Crows of the World. 2nd Edition. The British Museum (Natural History) , London 1986. ISBN 0565009796 .
  • Knud A. Jønsson, Pierre-Henri Fabre, Martin Irestedt: Brains, Tools, Innovation and Biogeography in Crows and Ravens. In: BMC Evolutionary Biology 12 (72), 2012. doi : 10.1186 / 1471-2148-12-72 .
  • John Latham: Index ornithologicus sive Systema ornithologiæ. London 1790. ( Online )
  • Steve Madge , Hilary Burn: Crows & Jays. Princeton University Press, Princeton 1994, ISBN 0-691-08883-7 .
  • Richard Meinertzhagen: Introduction to a Review of the Genus Corvus. In: Novitates Zoologicae 33, 1926. pp. 57-121. ( Online )
  • Roger D. Price, Ronald A. Hellenthal: Taxonomy of Philopterus (Phthiraptera: Philopteridae) from the Corvidae (Passeriformes), with Descriptions of Nine New Species. In: Annals of the Entomological Society of America 91 (6), November 1998. pp. 782-799.
  • Austin Roberts (Ed.): Roberts birds of Southern Africa . Voelcker Bird Book Fund , Cape Town 2005. ISBN 0-620-34053-3 , pp. 477-478.
  • CJ Uys: At the Nest of the Cape Raven . In: Bokmakierie 18, 1966. pp. 38-41.
  • Michel P. Valim: Type Specimens of Lice (Insecta: Phthiraptera) Held in the Museu de Zoologia da Universidade de São Paulo, Brazil. In: Papéis Avulsos de Zoologia (São Paulo) 49 (17), 2009. doi : 10.1590 / S0031-10492009001700001 , pp. 197-219.

Web links

Commons : Vulture ( Corvus albicollis )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Latham 1790 , p. 151.
  2. ↑ a b c d e f g h i j k l Brown et al. 2000 , p. 551.
  3. ↑ a b c d Goodwin 1986 , p. 132.
  4. ↑ a b c Madge & Burn 1994 , p. 182.
  5. ↑ a b c d e f g h Roberts 2005 , p. 724.
  6. ↑ a b Brown et al. 2000 , p. 550.
  7. ↑ a b Madge & Burn 1994 , p. 183.
  8. ↑ Uys 1966 , pp. 40-41.
  9. ↑ a b c d e f Brown et al. 2000 , p. 552.
  10. ↑ Diamond & Bond 2003 , p. 1096.
  11. ↑ Goodwin 1986 , p. 133.
  12. ↑ del Hoyo et al. 2009 , p. 551.
  13. ↑ Price & Hellenthal 1998 , p. 786.
  14. ↑ Ansari 1957 , p. 180.
  15. ↑ Valim 2005 , p. 200.
  16. ↑ Jønsson et al. 2012 , p. 23.
  17. ↑ a b c Glutz von Blotzheim & Bauer 1993 , p. 1653.
  18. ↑ Amadon 1944 , p. 16.
  19. ↑ Goodwin 1986 , p. 71.
  20. ↑ Meinertzhagen 1926 , p. 57.
  21. ↑ del Hoyo et al. 2009 , p. 640.
  22. ^ IUCN 2008 , accessed August 25, 2011.
This article was added to the list of excellent articles on October 29, 2011 in this version .