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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Feeding ecology and choice of colony sites of Black Terns Chlidonias niger on the peninsula of Eiderstedt, northern Germany.
Auteurs :	Hermann Hoetker, Auteur ; Claus Ivens, Auteur ; Heike Koester, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (126(3) 2005)
Article en page(s) :	203-214
Résumé :	The last stronghold of the breeding Population of Black Terns in Schleswig-Holstein (Germany) is the marshlands of the peninsula of Eiderstedt. The Black Tern population, however, is threatened there. In the breeding seasons of 2002 and 2003 we studied habitat availability and habitat selection of foraging Black Terns. Habitat studies were based on aerial and ground Surveys. They comprised land use, availability and state of ditches and availability of ponds (drinking ponds for cattle, 50 to 350 m(2) in size). At seven colonies we recorded altogether 1096 foraging flights of Black Terns. In most cases Black Terns foraged close to their colonies. The median distances between colonies and end points of flights were 530 in in 2002 and 422 in in 2003. Black Terns foraged over ditches, meadows (in particular sheep meadows), drinking ponds, silage and hay grasslands. We did not find any relationship between weather and distance of flights or habitats used. Black Terns undertook significantly longer flights in the nestling period than in the incubation period, and they used ditches significantly more often in the nestling period than in the incubation period. In 2002 (but not in 2003) fish comprised a significantly higher proportion of their diet during the nestling period than during the incubation period. Foraging Black Terns showed a significant preference for ditches, in particular those with open water surfaces. Except for drinking ponds all other habitats were used less frequently than expected by their surface availability in the study site. Black Tern colonies were situated in pure grassland sites without arable fields. There was a significant relationship between the amount of open water surface and the colony site selection.The following measures should be applied to improve the conservation status of Black Terns on Eiderstedt: Protection of extensive areas of meadows or grassland with a dense network of ditches and drinking ponds, increase of water level in the ditches, creation of new small water bodies by closing irrigation ditches or damming of whole irrigation ditch networks; continuation of effective measures of colony protection (provision of nesting rafts and fencing against cattle).

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