Frog consecration
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![Frog Harrier (Circus ranivorus) [1]](https://de.wikipedia.org/wiki/Datei:Circus_ranivorus.jpg)
Frog harrier ( Circus ranivorus ) |
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| Systematics | ||||||||||||
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| Circus ranivorus | ||||||||||||
| ( Daudin , 1800) |
The frog harrier ( Circus ranivorus ) is a bird of prey from the hawk family (Accipitridae). It is native to sub-Saharan Africa and inhabits swamp and marshland. Their distribution area extends from southern Sudan to the Cape of Good Hope . The frog harrier feeds on small mammals and passerine birds.
The population has not yet been widely estimated, but is probably 3000 to 6000 breeding pairs for southern Africa. The IUCN classifies the frog harrier as 
(= least concern - not endangered), although it has suffered severe habitat losses in many places due to the decline in wetlands.
features
Appearance and build
In contrast to the Eurasian harriers , frog harriers do not show any sexual dimorphism in color, but the females become larger and heavier than the males. The weight of both sexes is between 382 and 590 g, the body length between 44 and 49 cm. The wing length in males is 357–382 mm, that of the female 361–395 mm. The tail length is 187–243 mm in the male, in the female it is 215–242 mm. The tarsometatarsus measures 82–85 mm in male birds and 82–90 mm in females.
The head of the frog harrier is colored gray-brown, with the face veil typical of the consecration being set off from the rest of the head by a wreath of white feathers. Throat, chest and under wing-coverts are dashed white on a brown background and bordered with white on the shoulders. The abdomen and thighs are usually a uniform reddish brown, but in some cases they are also dashed in white. The white hand and cream-colored arm wings show a thin, dark band that ends with the slightly wider, dark wing edge. The tail feathers are banded black on the underside on a light background. On the upper side, the brown color dominates as the basic tone. The upper wing-coverts are covered with white and dark speckles. The arm and hand wings show the same dark banding on the upper side as on the underside, but the basic color is gray-brown. In contrast to most other harriers, adult frog harriers do not have a white rump, this one is rather reddish-light brown. The upper side of the tail feathers is banded dark on a light gray background.
Juvenile birds have dark brown head plumage that contrasts with light, cream-colored spots on the neck, throat, shoulders and front forehead. The top and chest are also more or less uniformly dark brown; the rump, which is lighter reddish brown in color, is an exception. A white band runs across the chest, the abdomen and trousers of juvenile frogs are lighter brown than the head and top. The under wing coverts are variably dashed in white on a dark brown background. The contrast between the gray arm wings and the sand-colored hand wings at the base is clearer than in adult animals. The hand wings are indistinctly and thinly banded in black, the tips are gray on the inner hand wings and black on the outer ones. The underside of the tail feathers is sandy brown, variably darkly banded and ends with a dark terminal band. Immature birds probably show a transitional dress from the juvenile to the adult phase, but there are no reliable findings on this.
Flight image
Frog ordinations show the typical of their species flight image by a sliding Gaukelflug characterized in a height of 5 to 20 meters above the ground. A series of a few weak wing beats alternates with a short glide phase. Distinguishing features in flight are the long, rectangular wings with slightly rounded tips, which the frog harrier holds in a V-position, as well as the slender body with a long, narrow tail.
Vocalizations
Acoustically, frog harriers are rather inconspicuous. During the mating season, a plaintive Tschiii-uk and a softer tougut of the male can only be heard near the nesting site . The female also uses the latter call as an answer when the male hands him prey with a pju or prrduk in the air. Female birds use Psiuw-psiuw-psiuw to beg for food. During the courtship flight the male calls with an ascending ouwiep ; a fast, aggressive Kekekekek serves as an alarm and warning call for both sexes; these calls are also common among other ordinations. In addition, frog harriers communicate by chuckling and cackling noises.
Spreading and migrations
The distribution area of the frog harrier is between 4 ° S and 35 ° S and extends from South Sudan to the Cape of Good Hope . It includes the southern coast of Africa, eastern South Africa , the northern half of Botswana , Zimbabwe , Mozambique west of Cabo Delgado and Nampula and all of Malawi ; from there it extends roughly along the Central African Rift across the borders of Tanzania , the Democratic Republic of the Congo and Uganda . In the north it extends to the southern Sudanese states of Central and Eastern Equatoria , in the northeast to the region of Lake Turkana in Kenya . In the west it also includes the eastern part of the Angolan Cuando Cubango . Smaller distribution islands are in northeast Tanzania, in Maniema and in Kwilu .
Frog harriers are resident birds and are usually sedentary. However, depending on the seasonally fluctuating water levels, they may react to changed habitats and food supplies. Juvenile frog harriers also leave their parents' breeding grounds and settle elsewhere. The sightings of frog harriers extend beyond the distribution area to Somalia and southern Ethiopia .
habitat
The habitat of the frog harrier consists primarily of permanent wetlands such as marshland, swamps or lake shores, for example in the Okavango Delta , which houses a large part of the population. The decisive factor is sufficient annual rainfall of more than 300 mm. The vegetation of the habitat usually consists of reeds , but the frog harrier also hunts over grasslands or wheat fields and other agricultural areas. It occurs at heights of up to 3000 m, in eastern Africa mostly above 1500 m.
Way of life
nutrition
During the day, frog harriers hunt in deep, fluttering flight over extensive vegetation, where they locate their prey both visually and acoustically. The flight altitude is usually only one to three meters above the ground, the flight speed is 20 to 30 km / h. Once they have identified a potential prey, they drop abruptly and grab it from flight. Brooding frogs spend between 40 and 50% of the day foraging for food.
The range of prey includes primarily small rodents, especially lamellar tooth rats ( Otomys ) and African welted grass mice ( Rhabdomys ). The distribution area and the choice of habitat of the frog harrier depends heavily on the occurrence of these two genera. The second main component of the diet is made up of birds, primarily passerines (passeriformes); however, the size of the prey ranges up to small ducks and pigeons. The proportion of birds and mammals in the diet fluctuates greatly: during the breeding season, mainly mice (around 80%) are captured, with birds becoming fledged, the percentage of birds increases sharply and sometimes even exceeds that of mammals. The frog harriers prey on reptiles and amphibians less often - contrary to their German and scientific species name ( ranivorus , Latin for "frog eater" ). When the opportunity arises, it also eats other nestlings, eggs, carrion or fish.
Social behavior
Frog harriers defend their breeding grounds against intruders. They patrol in flight along the territorial boundaries and let their legs hang with clearly visible claws. If a foreign frog harrier invades the area, they attack it by trying to grab it from the air and pull it to the ground. Like other harriers, the frog harriers occasionally gather in smaller flocks outside of the brood and seek common roosts.
The settlement density has so far only been researched in South Africa, a corresponding study found 8 nests in the investigation area of 10 km².
Reproduction
The breeding season of the frog harrier varies greatly depending on the geographical latitude. In equatorial Kenya it is between June and October; in southern Zambia and Zimbabwe , breeding takes place between December and August. In South Africa most pairs breed between September and January, but the first broods begin as early as May and the last occur in February.
During the courtship season, the frog harrier performs acrobatic flight maneuvers, as can also be observed with other harrier species. The birds soar with intense wing beats in a spiral to a height of 70 to 400 meters. There they then accelerate horizontally before they take a sinusoidal trajectory in which they alternately drop, then gain altitude again and finally drop again. At the peak of every upswing, the frog consecration calls out with a high, ascending ouwiep ; occasionally she also performs backflips in flight. These U-shaped maneuvers are completed ten to twelve times per minute; Overall, these flights take 2-3 minutes, but in individual cases up to 20 minutes. The birds then tumble towards the ground in a circling, dancing movement that is reminiscent of a falling leaf, before they catch themselves about two meters above the ground and then land on the nesting site. These courtship flights can be observed in both sexes, but males perform them more intensely and around twice as often as females. Although frog harriers are monogamous and remain loyal to their partner for several years, this courtship ritual can be observed regularly. It is therefore not only used for partner recruitment, but may represent an act of couple bonding.
Copulation usually occurs near the nesting site. The female flexes the body and holds the tail slightly to one side or raised, whereupon the male lands on the female from a deep, slow glide. It clenches its claws into a fist to avoid injuries, while it keeps its balance by flapping its wings. The copulation itself takes about 5-6 seconds, then both partners clean their plumage and cloaca .
The female lays her eggs in a flat, simple ground nest with a diameter of about 40-60 cm, which, depending on the environment, consists of thin twigs or tufts of grass. It is mostly found in reed beds just above the water level, more rarely in grain fields or other dry vegetation. During the brooding and rearing of the chicks, the male takes care of the procurement of food. The prey is given to the female in the air by the approaching male calling and the female being blown up from the nest. It approaches the male and flies under him, whereupon the male tosses the prey slightly upwards. The female uses the prey's moment of inertia and grabs it out of the air. The clutch usually consists of 2–5, on average 3.3 eggs, which are usually laid at three-day intervals. They are initially bluish-white and turn a dirty white tone as they brood. Their shape is short oval, the dimensions of the eggs are on average 32.4–40.3 × 41.0–54.5 mm. They weigh around 30 g and have a volume of 23.5–33.5 cm³; smaller females tend to lay the larger eggs. The chicks hatch after 32-34 days and fledge after a further 38-40 days. The youngest chick often starves to death because it cannot prevail against its larger and stronger siblings.
Systematics
The frog consecration was first described in 1800 by François-Marie Daudin as Falco ranivorus . According to the classical system of the genus Circus established by Stresemann in 1924 , it was, like other tropical harriers, for a long time a subspecies of the Eurasian Marsh Harrier ( C. aeruginosus ). Peters raised it to species status in 1931, in which later authors followed it. Historically, the frog harrier belongs to the branch of the consecration whose members tend to inhabit wetlands. According to DNA analyzes, it is the sister taxon to the East Asian mangrove antler ( C. spilonotus ).
No subspecies are recognized for frog consecration. Some authors placed birds from Central Africa in their own subspecies aequatorialis , but this did not find general recognition.
Existence and endangerment
Frog harrier populations have declined across Africa over the past century. There was a slump in Kenya in particular, and no broods have been reported in recent years. There was also a sharp decline in the population in the former Transvaal : The 500 to 1,000 breeding pairs that were determined for 1987 are unlikely to be reached today. Although the number of breeding pairs for the whole of South Africa was still estimated at around 3,000–5,000 in 2000, observers also doubt these numbers in view of the general population decline. Even in the Okavango Delta , a focus of the world population, the number of breeding pairs has decreased in recent decades; in Lesotho the species is considered extinct. Only in Uganda do populations seem to be recovering slightly, where as many birds were sighted in 2005 as they were last seen in 1970. Ferguson-Lees and Christie estimated the total population for 2000 to be less than 10,000 birds.
These declines are primarily due to the drainage of wetlands; It is also unclear what proportion of pesticides and water pollution are in the depletion of stocks. In Uganda, the frog harrier is on the state's warning list. Overall, however, the species is still not endangered in the opinion of the IUCN .
Sources and References
literature
- James Ferguson-Lees , David A. Christie: Raptors of the World. Houghton Mifflin Harcourt, 2001, ISBN 0618127623 , pp. 496-498.
- Austin Roberts: Roberts birds of Southern Africa. Voelcker Bird Book Fund, Cape Town 2005. ISBN 0-620-34053-3 , pp. 501-502.
- Robert E. Simmons: Harriers of the World: Their Behavior and Ecology . Oxford University Press , 2000, ISBN 0198549644 .
Web links
- Circus ranivorus on www.globalraptors.org
- Circus ranivorus onthe IUCN Red List of Endangered Species . Listed by: BirdLife International, 2009. Retrieved August 20, 2010.
- Literature on the frog harrier on the Global Raptor Information Network
Individual evidence
- ^ Image by Robert E. Simmons, FitzPatrick Institute.
- ↑ a b c d e Roberts 2005, p. 501.
- ↑ a b c d e f g h i j James Ferguson-Lees, David A. Christie: Raptors of the World. Houghton Mifflin Harcourt, 2001, ISBN 0618127623 , pp. 496-498.
- ^ Robert E. Simmons: Harriers of the World: Their Behavior and Ecology . Oxford University Press , 2000, ISBN 0198549644 , p. 13.
- ↑ a b c d e f g Species account: African Marsh Harrier Circus ranivorus. globalraptors.org, September 15, 2009. Retrieved August 23, 2010.
- ↑ Simmons 2000, p. 103.
- ↑ Simmons 2000, pp. 252-258.
- ↑ Simmons 2000, pp. 300-301.
- ↑ Simmons 2000, pp. 59-70.
- ↑ Simmons 2000, pp. 43-45.
- ↑ Simmons 2000, pp. 217-225.
- ↑ Simmons 2000, p. 25.
- ↑ Circus ranivorus in the IUCN Red List of Endangered Species . Listed by: BirdLife International, 2009. Retrieved August 20, 2010.