Snail harrier

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Snail harrier
Snail Harrier - adult animal

Snail Harrier - adult animal

Systematics
Order : Birds of prey (Accipitriformes)
Family : Hawk species (Accipitridae)
Subfamily : Buzzard-like (buteoninae)
Genre : Snail harrier
Type : Snail harrier
Scientific name of the  genus
Rosthramus
Lesson , 1830
Scientific name of the  species
Rostrhamus sociabilis
( Vieillot , 1817)

The snail harrier ( Rostrhamus sociabilis ), also known as the snail kite , is a bird of prey from the hawk family (Accipitridae).

description

Young bird with apple snail
Female snail harrier

The snail harrier reaches a length of 39 to 48 centimeters and a wingspan of 99 to 115 centimeters. The wing length is 328 to 382 millimeters, the tail length 158 to 210 millimeters, and the beak measures between 28 and 40 millimeters. The weight of an adult male is up to 385 grams, females are slightly heavier at 415 grams. The snail harrier has long, broad, deeply fingered wings that are strongly rounded at the bend of the wing, a long tail, a white rump and white under- tail- coverts . The upper side of the tail is black in the male, the lower side shows a clear, quite wide black subterminal band. The thin hooked beak is unmistakable and a perfectly adapted tool for opening snail shells. The pointed, narrow upper beak curves in a sickle shape over the lower beak. The iris of both sexes is bright red. The plumage of the adult male is uniformly dark blue-gray. The long legs are orange-red. The back and top of the wings of the females are dark brown, with the exception of the arm and hand wings, most of the cover feathers are lined a little lighter. The underside is a little lighter brown and irregularly spotted with white. The mostly almost pure white of the throat changes into a dark brown spot on the chest of varying degrees. In flight, the broad, light field in the area of ​​the middle hand wings and the reddish-brown coloration of the lower wing covers are noticeable in the female. Up to the barrel, the lower legs of both sexes have the same color as the abdominal plumage. The featherless areas around the eye, the wax skin and the legs are yellow-orange. The juvenile birds look similar to the female, but the top of the head is striped and the underside is cream-colored and shows a clear stripe pattern. The iris is brown, the bridle is cream colored and the legs are yellowish.

distribution

light green: breeding areas that are cleared in winter
yellow field: breeding areas in Florida and Cuba

The snail harrier occurs in four subspecies in tropical South America , Cuba , eastern Mexico , the Caribbean, and central and southern Florida in the United States . R. s. sociabilis is distributed from Nicaragua to South America. The distribution area of R. s. major extends from southeastern Mexico to Guatemala , R. s. plumbeus (sometimes referred to as the Everglades snail kite) occurs in the Everglades in the Kissimmee River valley , in the Okeechobeesees area and on the St. Johns River . In 2007 this subspecies was first observed outside Florida, in North Carolina . The breed R. s. levis lives in Cuba and the Isla de la Juventud .

Food, way of life and reproduction

The snail harrier is a sociable animal. Colonies made up of up to 200 birds have been observed. The Everglades' snail harrier population feeds almost exclusively on the Florida apple snail ( Pomacea paludosa ). When the snail harrier spots a snail, it plunges down, grabs the snail with its claws out of the vegetation or out of the water and transports it in its beak to its preferred perch (e.g. the branch of a bush). Then he holds it with one or both claws and cuts through the spindle muscle nerve with his highly specialized hooked bill so that the closed snail shell lid opens. Now the snail harrier can loosen the snail from its house and eat it. In other parts of the range, the snail harrier feeds on freshwater snails of the genus Marisa and freshwater crabs of the genus Dilocarcinus . In Florida, the snail pond is true to location, making it very vulnerable to droughts and other changes in hydrology . The breeding season in Florida is from December to August, in Suriname from January to September and in Argentina from August to March. The nest is built on a branch hanging over the water to protect it from terrestrial predators. It has a diameter of 30 to 40 centimeters, a depth of 10 to 30 centimeters and is padded with rushes, grass and herbs. The clutch consists of two to three (rarely five) white eggs with brown spots. The eggs will hatch after 26 to 28 days. The young fledged after 23 to 30 days.

status

The snail harrier is not endangered in Central and South America. In the Everglades, on the other hand, the population had reached its all-time low in 1964 with only 15 specimens. In 1968 there were between 50 and 60 copies. The censuses between 1969 and 1994 showed that the population is subject to great fluctuations. By the early 1980s, the population rose to 650 birds, after a peak of 668 in 1984, the population dropped to 326 in 1987. In 1994, the population in the United States recovered to 650 specimens and is now around 800 to 1,000 individuals. In 1982, 55 specimens of the Cuban breed lived in the swamps of the Zapata Peninsula . The main threat is habitat loss due to the drainage of swamps. Further threats are the use of herbicides and habitat changes by invasive plants such as the thick-stemmed water hyacinth ( Eichhornia crassipes ) and the Melaleuca tree ( Melaleuca quinquenervia ).

Individual evidence

  1. ^ T. Halliday: Vanishing Birds - Their Natural History and Conservation . Sidgwick & Jackson, London 1978, ISBN 0-283-98391-4 .

literature

  • James Ferguson-Lees , David A. Christie: Raptors of the World. Houghton Mifflin, Boston 2001, ISBN 0-618-12762-3 .
  • SE Haas, RT Kimball et al .: Genetic divergence among Snail Kite subspecies: implications for the conservation of the endangered Florida Snail Kite Rostrhamus sociabilis. In: Ibis. 151, 2009, pp. 181-185.

Web links

Commons : Schneckenweih ( Rostrhamus sociabilis )  - album with pictures, videos and audio files