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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Distribution and population trends of the Sandwich Tern Sterna sandvicensis in the Baltic Sea
Auteurs :	Christof Herrmann, Auteur ; Hans Wolfgang Nehls, Auteur ; Jens Gregersen, Auteur ; Wilfried Knief, Auteur ; Rolf Larsson, Auteur ; Jaanus Elts, Auteur ; Maria Wieloch, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (129(1) 2008)
Article en page(s) :	35-46
Résumé :	At the beginning of the 20(th) century, the Baltic Sea did not form part of the breeding range of the Sandwich Tern. However, during the first half of the century the species expanded its range gradually to the northeast, colonising Skane in 1911, and the Swedish east coast during the 1930s. Starting with the formation of a colony on the island Heuwiese (Germany, Mecklenburg-Western Pomerania) in 1957, the Sandwich Tern continued its range expansion to the southern coasts of the western and central Baltic, becoming a breeding bird in Estonia in 1962 and in Poland in 1977. The range expansion and positive population development in the Baltic during the 1950s/1960s happened at a time, when the North Sea population declined dramatically. This indicates that the colonisation of the Baltic Sea could have been a response to the worsening of environmental conditions there. The Baltic breeding population grew constantly and reached about 2,500 breeding pairs (bp) by the end of the 1970s. Since then, despite some fluctuations and frequent shifts of breeding sites, the population size can be considered as more or less stable. More detailed surveillance data from the mid-1990s until now reveal a population size fluctuating at 2,000-3,500 bp. The main conservation measure for the Sandwich Tern in the Baltic is the protection of suitable breeding sites. These are especially small islands covered by low grass vegetation, without human disturbances and predatory mammals. The presence of Black-headed Gulls is an essential condition for the choice of the breeding place.

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