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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	[Microhabitat selection and dispersion suggest interspecific competition between Blackcap Sylvia atricapilla and Garden Warbler S. borin in a wood-meadow ecotone.]
Auteurs :	Ortwin Elle, Auteur
Type de document :	Article
Dans :	Vogelwelt (Die) (123(1) 2002)
Article en page(s) :	9-16
Résumé :	This study deals with interspecific territoriality of Blackcap and Garden Warbler on a 45 ha study plot of syntopic occurrence, situated in a wood-meadow ecotone. Little mutual spatial overlap of the bird territories, along with similar habitat preferences of both species, are strong arguments in favour of interspecific competition for space. There are no clues to superiority of one species over the other. Over a period of three years 39 territorial Blackcaps and 38 Garden Warblers were investigated by means of multivariate, statistical methods (factor analysis, cluster a., discriminant a.) concerning their habitat choice, which in this study is defined by the selection of vegetation structures at the microhabitat level. Analysing each study year separately, distinct interspecific differences of habitat choice are noticeable, along with little mutual spatial overlap of the territories of both species. Quantitative evidence is given by discriminant models, assigning between 75% and 88% of the territories correctly to the species based on the structural properties. In contrast, analysing the three study years together, intraspecific variability of habitat choice increases in relation to interspecific variability. Merely 66% of all territories are assigned correctly to the species by a discriminant analysis. Along with increasing spatial overlap of the territories (projecting the three years together onto a map), this low value indicates a high degree of interspecific similarity of the spectrum of selected vegetation structures. Based on these facts it is concluded that the annual establishment of the bird territories after return from wintering areas is influenced by interspecific competition, leading to the distinguishable spatial and structural patterns. Concerning the investigated study plot, competition is considered to be more decisive for the observed annual, mutual exclusion of both species than possible, interspecifically differing habitat preferences, which proved to be rather similar on long-term view. Accordingly, interspecific competition, being effective only within a year, is only detectable by the separate analysis of each year, whereas the potential of habitat choice of each species is underrated by this single-year approach. The potential is better revealed by the combined analysis of the complete study period.

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