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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	The nature reserve Leyhorn a suitable breeding habitat for the Pied Avocet Recurvirostra avosetta?
Auteurs :	Franke Freise, Auteur ; Klaus-Michael Exo, Auteur ; Bernd Oltmanns, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (127(3) 2006)
Article en page(s) :	175-186
Résumé :	At the beginning of the 1980s the Leybucht (Lower Saxony, Germany) was one of the most important breeding sites for Pied Avocets in western continental Europe. Since the early 1990s the number of breeding pairs decreased dramatically. This decline was associated with a shift of the main breeding sites: Avocets switched from their former breeding sites in foreland salt marshes of the eastern Leybucht to inner dike sites of the nature reserve Leyhorn, mainly to sandbanks within the storage reservoir. The nature reserve Leyhorn resulted from a coastal protection programme in the second half of the 1980s. Biological studies accompanying the construction work raised the question whether the nature reserve, especially the storage reservoir, offered suitable breeding sites for Avocets. Observations indicated that particularly during the period of chick rearing, heavy losses occurred. To prove the suitability of the nature reserve as a breeding ground for Pied Avocets, breeding biology was studied for the first time in detail in 2003. We investigated the effects of flooding, predation, food availability, vegetation an weather on hatching and fledging success. With less than 0.1 fledglings per breeding pair in both study sites, fledging success was very low. Fledging success was much lower than that apparently required to maintain the current population size. Losses were mainly due to flooding of nests and predation, two causes which cannot be eliminated in the long term. Moreover, in the medium term, the ongoing succession of the vegetation will cause the loss of those breeding sites which are safe from flooding. Therefore, the nature reserve Leyhorn does not seem to be an ideal breeding ground for Avocets. It appears that the traditional foreland breeding sites in the salt marshes are more suitable.

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