Wahlbergsadler
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Wahlbergsadler |
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| Hieraaetus wahlbergi | ||||||||||||
| ( Sundevall , 1851) |
The Wahlberg Adler ( Hieraaetus wahlbergi , Syn. : Aquila wahlbergi ), also Silberadler called or Wahlberg Adler written is in the Afrotropic occurring prey from the family of the Accipitridae (Accipitridae), which in its size to that of an Milan corresponds.
The IUCN specifies that the Wahlbergsadler is not at risk ( least concern ). No subspecies are distinguished.
Appearance
Body measurements
The Wahlbergsadler reaches a body length of 53 to 61 centimeters, of which 21.5 to 23 centimeters are made up of the tail plumage in the male and between 23.5 and 25 centimeters in the female. The wings are 40 to 43.5 centimeters long in the males and 43.5 to 44.5 centimeters in length in the females. The wingspan is 130 to 146 centimeters. The weight of the males is between 437 and 845 grams, the females weigh between 670 and 1400 grams. The eyes of adult birds are yellow. The beak is blue-gray, the wax skin is greenish yellow. The feet are yellow in both sexes. Aside from the size difference, there is no noticeable gender dimorphism .
Color morphs
The Wahlbergsadler occurs in a number of color morphs, ranging from dark brown to predominantly white-feathered individuals. The most common color amorphous has sepia colored plumage. What they all have in common is the small face compared to the body, a small, often not clearly recognizable feather hood and largely feathered legs. The tail is long compared to the body size and the long wings almost reach the tip of the tail.
In the dark color morphs, the wing covers are either lighter or they have lighter feather edges. Occasionally the belly or the head sides are lightened compared to the rest of the plumage. In the much rarer light color morphs, wing-coverts, arm and hand wings and the rump are usually gray-brown, the tail plumage is blackish. Most of these individuals have blackish longitudinal lines on the head or chest. There are also color morphs with a pale brown or dark brown plumage, with a blackish or whitish head.
Possible confusion
The Wahlbergsadler can be confused with the booted eagle , which also occurs in light and dark color morphs. Light color morphs are more common in this species. The distinguishing features of the dark color morphs of both species include a light, U-shaped spot in the transition area from the back plumage to the tail plumage and a lightened shoulder area, which is only typical for the booted eagle. Light color morphs of the booted eagle have a darker head.
Brown color morphs of the mountain eagle can be distinguished from other dark birds of prey, such as the black kite and the frog harrier , by the feathered legs.
Distribution area
The Wahlbergsadler is a raptor of the Afrotropic ecozone. Its distribution area extends from the south of Mauritania , Senegal and Gambia to Sudan , Eritrea and Ethiopia . In a southerly direction, its distribution area extends over east Africa to Botswana and the north and east of the South African Republic. It also occurs in Angola , as well as the north and inland areas of Namibia . The mountain eagles observed in the northern part of the range are usually non-breeding individuals. The main areas of distribution include Kenya and Tanzania , as well as Malawi , Mozambique and Zimbabwe . It is absent in the wooded regions in southern Cameroon as well as in Gabon , the Congo and the Central African Republic .
Migratory behavior
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Only small parts of the populations are resident birds or only migrate over short distances. The greater part of the population are long-distance migrants, with individual birds migrating from the east of the South African Republic to the south of Sudan. Populations south of a line, which range from Angola, via Namibia and Malawi to Mozambique, move north after the breeding season and cannot be observed in southern Africa from February / April to the end of August. During this time, the population in Tanzania and Kenya is also lowest. During this migration, elected mountain eagles can be seen in large numbers in parts of the Central African Rift . Their return begins at the end of July and continues until the beginning of September. Telemetric studies have shown that the southernmost populations move furthest to the north and "fly over" populations that show far less pronounced migratory movements or that are sometimes even resident birds. The West African populations, whose distribution area is north of the equator, also show migratory movements, but travel significantly shorter distances.
habitat
The mountain eagle by choice occurs in sparsely forested regions, savannas, in forests along rivers, in the thorn bush savannah, on open grasslands and in regions with a dense mosaic of open and wooded areas. He avoids arid regions and mountains. In Ethiopia, however, it also breeds in the highlands. Its height distribution extends from the lowlands to altitudes of 1800 meters. Occasionally it also occurs at 2800 meters.
Way of life
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Apart from the migration, when large, loose flocks can be seen, the Wahlbergsadler lives solitary or in pairs. Its diet consists of reptiles, mammals and birds. For most of the Wahlbergsadler none of these groups dominate. But it also eats frogs and insects such as beetles, grasshoppers and termites.
Most of the mammals he hits are rodents, and occasionally young hyrax and bats. The spectrum of birds that it hits is very large and ranges from larks and the nestlings of starlings to guinea fowl, herons and small species of birds of prey. Occasionally owls are also part of its prey spectrum. A breeding pair of elected mountain eagles that was observed more closely raised its offspring exclusively with nestlings of black-necked and cattle egrets. They captured the nestlings by circling above the breeding colony and then dropping onto the nests to grab nestlings. Occasionally the breeding pair also worked together, with one of the two birds circling so close over the colony that the adult herons flew up and the second elected mountain eagle used this to prey on young herons. But they are also hide hunters who look for prey from an exposed branch. During bush fires, they also catch insects that the fire scares off. Wahlbergsadler have also been seen snatching prey from the crested eagle.
Reproduction
The breeding season of the Wahlbergsadler falls in most of the distribution area in the period from November to February. Only West African populations north of the equator breed from June to November.
The nest is comparatively small and has a diameter of 45 to 80 centimeters and is between 25 and 60 centimeters high. It is usually 8 to 12 meters above the ground. Preferred nesting trees include acacias, baobabs, and eucalyptus trees. The nesting trees are often close to water.
The clutch consists of one or two eggs that are incubated for 44 to 46 days. The nestlings are usually fledged between 70 and 75 days of age.
literature
- J. Ferguson-Lees, DA Christie: Raptors of the World. Christopher Helm, London 2001, ISBN 0-7136-8026-1 .
