Habitat selection and interspecific territoriality in sympatric warblers at two Italian marshland areas

Abstract

The warbler communities of two marshland areas of north-western Italy with a partially different vegetation were studied for 3 years in order to determine their ecological organization, especially with respect to interspecific coexistence. In terms of general habitat selection most species (i.e. Marsh Warbler Acrocephalus palustris, Reed Warbler A. scirpaceus, Great Reed Warbler A. arundinaceus, Sedge Warbler A. shoenebaenus and Savi's Warbler Locustella luscinioides) are found predominantly in reed beds (Phragmites sp.), the Marsh Warbler, however, is also found in areas with low trees and shrubs. On the contrary, Cetti's Warbler Cettia cetti is found mainly in alder-willow groves and in wooded habitats with tangled vegetation. Within reed beds the Great Reed Warbler occurs mostly near open water with the Savi's Warbler and the Marsh Warbler occurring mostly near the land or in the centre of the reed bed. The territorial distribution of the Marsh Warbler is affected by the presence (or absence) of the Great Reed Warbler to a little extent. Using the analysis of niche differentiation for the distribution of species on vegetation, the Marsh Warbler appears more generalist than the Great Reed Warbler and the Sedge Warbler is the most specialised. Resource use and vertical distribution of species differed between the two study sites, and depended on whether the birds were observed foraging, resting or singing. Playback experiments suggest that the Great Reed Warbler defends territories against the Marsh Warbler, and possibly some other species, even though the lack of overlap in the Great Reed Warbler and the Marsh Warbler territories is partly attributable to habitat selection.