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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Why do Red-backed Shrikes not build better concealed nests?
Auteurs :	H. Jakober, Auteur ; W. Stauber, Auteur
Type de document :	Article
Dans :	Journal of Ornithology (143(4) OCT 2002)
Article en page(s) :	397-404
Langues:	Anglais
Résumé :	Between 1983 and 1999, we located and monitored 1432 Red-backed Shrike (Lanius collurio) nests near Goppingen (Baden-Wurttemberg, 48degrees39N/09degrees47E) in southwest Germany. We categorised the visibility of the nests in three groups: exposed, semi-concealed and concealed. From 1997 to 1999, we recorded the visibility of 296 nests from a distance of 1 m and 2 m from above and from the side in each of the four cardinal directions. 47% of the nests were exposed. Only 16% of them were so well concealed that we could see less than half of the nest from a distance of 1 m in the most favourable direction. A Visually searching predator should therefore be able to detect almost every nest. The reproductive success was nevertheless higher in nest sites with lower visibility. We suppose that exposed nests are additionally at risk from predators which detect them by chance without searching for them systematically. The number of the exposed nests increased as the breeding season progressed. This is also true if nest sites at a higher elevation and those in fruit-trees, which are more often exposed, are excluded. We assume that only a certain proportion of the nests are poorly concealed because of a lack of better alternatives, especially in replacement broods. Several possible advantages of the poorly concealed nest are discussed.

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