Egret runner

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Egret runner
Egret runner (Dromas ardeola)

Egret runner ( Dromas ardeola )

Systematics
Class : Birds (aves)
Order : Plover-like (Charadriiformes)
Family : Egret runner
Genre : Dromas
Type : Egret runner
Scientific name of the  family
Dromadidae
Gray , 1840
Scientific name of the  genus
Dromas
Paykull , 1805
Scientific name of the  species
Dromas ardeola
Paykull , 1805

The Crab Plover ( Dromas ardeola ) is a breeding bird colonies in the coasts of the Indian Ocean . The conspicuous black and white bird digs nesting holes in the sand dunes. Its systematic position is unclear, but it is usually assigned to the plover species . No subspecies are distinguished.

features

The heron runner reaches a body length of 40 centimeters. The wingspan is 66 centimeters. A sexual dimorphism that can be used in field ornithology does not exist. At most, males have slightly larger and thicker beaks than females on average.

From the neck down to the Crab Plover with his long legs, slim body and a long neck to a reminiscent avocets . The head is, however, greatly enlarged to support a massive beak. This beak is black, compressed on the sides and has a sharp point. The bird can strike powerfully with it like a dagger and pierce crab shells.

The plumage is mainly white. The front back and the wing feathers are black. The immediate area around the eye is also black; This makes the eye look particularly large from a distance. The tail is colored gray. In the youth dress, the black plumage areas are colored gray. There is also a characteristic black and gray line drawing on the vertex; in rare cases this drawing can also be found in adult birds.

The long legs are blue-gray in color. The foot is anisodactyl , the back toe is well developed. The front toes with basal webbed connected. Most of the time the heron walker slowly paces the mudflats; but it can also run fast in the hunt for prey.

distribution and habitat

The breeding areas of the heron runner are largely limited to the Red Sea and the Persian Gulf . The Handbook of the Birds of the World lists nine colonies that were the only breeding areas known to experts at the time of printing (1996):

Distribution area of ​​the heron runner
  • Iran : Karan Island, 1500 couples
  • Iran: a colony of 20 couples
  • Iran: a breeding area with only two pairs
  • Abu Dhabi : Abu al-Abyad Island , 280 couples
  • Abu Dhabei: Umm Amin Island, 85 couples
  • Oman : Masira Island , 85 couples
  • Saudi Arabia : sandbanks in front of al-Wajh
  • Saudi Arabia: Farasan Islands , 110 pairs
  • Somalia : Islands of Aibat and Saad ad-Din, number of pairs unknown

In the meantime, more colonies have been discovered off the coast of Eritrea . In the Dahlak Archipelago and on the Howakil Islands there are therefore thirty other colonies with over 5000 breeding pairs, which is more than in all previously known colonies combined.

Outside of the breeding season, egrets roam widely and can then be found on the entire east coast of Africa : often south to Tanzania , occasionally further to South Africa . Also, Madagascar and the Seychelles are visited, as well as the west coasts of India and Sri Lanka , and some birds even get to the Andaman Islands and as far as Thailand . Due to the uncertainty regarding the distribution area, the movements of the trains are difficult to determine in detail. However, according to research by Wetlands International , the majority of the population moves south and east in the period from August to November and returns to the breeding areas in March and April.

The habitat are sandy beaches, river deltas and lagoons. You will never find the heron runner further than 1 km from the sea.

Way of life

activity

Egret runner not only breed in colonies, but outside of the breeding season they are usually found in large flocks. These can contain up to 1000 individuals, but become smaller as the distance from the breeding colonies increases. During the breeding period, egrets are crepuscular and nocturnal. Outside the breeding season, they are active at all times of the day and night, but mostly continue at night.

food

Egret runners pace the shallow water in search of food. If they spot a prey, run after it and spear it with a quick blow.

The main food of the egrets consists of decapods . Small crabs are swallowed whole. In the case of large specimens, the legs and scissors are torn off first, then the body is divided with blows of the beak. The shape and size of the beak are ideal for breaking open even tough armor.

Mollusks and worms make up a smaller proportion of the diet. At the Iraqi coast you Reiherläufer also has the capture of mud jumpers observed.

Reproduction

The breeding season of the herons begins in April and lasts until June, regionally also until July. Egret runners are believed to live in seasonal monogamy . Their breeding behavior shows some noticeable deviations from other plover species . No other plover species breed in caves, and it is only in this species that the young do not flee the nest.

The caves are mostly dug in low dunes. These are corridors that are 1 to 2.5 m long and 20 cm wide. They are dug down at an angle so that the brood chamber at the end of the passage is about 50 cm below the entrance. The corridors are usually not straight, but change direction once or several times. Almost always only one egg is laid, only in rare cases there are two eggs in the clutch. This egg is unusually large with a size of 6 × 4.5 cm. It is pure white and does not have the patterns that other plover species have in eggs. The reason for this is probably that a cave-breeder does not need to camouflage its eggs.

Young birds are likely to be looked after by both partners. Exactly this is not yet known. The young are unable to walk or stand at the beginning and stay in the nest for a few days ( nestling ). During this time they are fed by the adult birds.

Systematics

The heron runner is one of the most problematic birds in terms of its systematic position in the bird kingdom. The anatomy shows many similarities with the plover-like , and here heron-walkers are occasionally placed near the triele or the curlew- like. The similarity of the beak to that of the crab triel is striking . However, this could have been caused by convergent evolution , since both birds have the same main food. Because of their plumage, egrets have been placed close to the avocets , and it has occasionally been suggested that the egret might be related to the hornbill or seagull .

Mostly, however, the egret runner is assigned to the plover-like. According to a study published in July 2010 based on molecular biological work, the egret is the sister group of the curlew-like (Glareolidae).

Egret runner and people

There is hardly any contact between egrets and humans. Globally, the bird is also not threatened, as its breeding areas are mostly on remote, uninhabited islands. Even an influence of the frequent oil spills in the Persian Gulf on the population numbers could not be determined. Only off the coast of Eritrea does it regularly happen that fishermen plunder the clutches of birds on the islands.

Sources and further information

Sources cited

Most of the information in this article is taken from the source given under literature; the following sources are also cited:

  1. ^ Richart Chandler: Shorebirds of the Northern Hemisphere . Christopher Helm Publishing House, London 2009, ISBN 978-1-4081-0790-4 , p. 51
  2. ^ A b G. de Marchi, G. Chiozzi, D. Semere, P. Galeotti, E. Boncompagni, M. Fasola: Nesting, overwintering, and conservation of the Crab Plover Dromas ardeola in central Eritrea . In: Ibis 2006, Vol. 148, No. 4, pp. 753-764
  3. ↑ Simon Delany, Derek Scott, Tim Dodman, David Stroud (Eds.): An Atlas of Wader Populations in Afrika and Western Eurasia. Wetlands International , Wageningen 2009, ISBN 9789058820471 , p. 36
  4. ↑ Sergio L. Pereira, Allan J. Baker: The enigmatic monotypic crab plover Dromas ardeola is closely related to pratincoles and coursers (Aves, Charadriiformes, Glareolidae). Genetics and Molecular Biology 33 (3): 583-6 July 2010  DOI: 10.1590 / S1415-47572010000300033

literature

Web links

Commons : Heron Runner  - Collection of images, videos and audio files