Franz Hölzl



PDF im Hochschulschriften-Service der Universität Wien

Population Density, Habitat Preferences and Nest Predation and of the River Warbler (Locustella fluviatilis) in the Donau-Auen National Park, Eastern Austria.

The floodplain forest system of the Danube east of Vienna has been used for forestry and agriculture for centuries and was affected by several river regulation measures leading to dramatic habitat changes and fragmentation of the floodplain. Nevertheless, the alluvial forests in Lower Austria are still one of the most important breeding areas for the river warbler in Austria and Central Europe. The aims of this study were to assess the present river warbler density in the Donau-Auen National Park; to evaluate the importance of published habitat requirements and food preferences for the river warbler population in the floodplain forest east of Vienna; and to test if nest predation differs between river warbler territories and randomly selected sites in the floodplain. Our results show that the river warbler density decreased over the last few decades from 1.8–1.9 breeding pairs/10ha in 1983 to 0.12 in 2009. Published habitat requirements of the river warbler are in line with the results of our study. At Donau-Auen National Park river warblers only colonize the regularly flooded forest area, where they prefer forest sites with a high herb layer and a high abundance of Hymenoptera. The experimental exposure of artificial nests showed a lower predation risk at river warbler territories compared to control sites. Our results indicate that selection of breeding territories in river warblers is driven by vegetation structure, food availability and spatial differences in nest predation risk. The decline of river warblers in the studied Danube floodplains east of Vienna is − most likely − related to habitat changes due to river regulation measures, which, besides changing vegetation structure, also may have been affected food availability and nest predation risk.

Winner of the National-Park-Prize 2013

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