Michael Tiefenbach

michitiefenbach@gmx.at

PDF der Diplomarbeit im Hochschulschriften-Service der Universität Wien


Habitat selection in foraging European Rollers (Coracias garrulus L.) in Eastern Austria

The population of the European Roller in northern and central Europe has suffered a dramatic decline during the late 20th century. This decline has often been attributed to changes in land use negatively affecting breeding success, mainly due to degrading quality of foraging habitats. However, so far empirical studies determining the habitat quality for Rollers in the context of foraging are missing. We studied the selection of foraging habitats by Rollers in eastern Austria. Habitat preferences were quantified by data on the use of two important artificial perch types, power lines and wooden poles, by hunting Rollers in the years 2002+2004 and 2002, respectively. All perches included in our analyses were located within a distance of less than 1.2 km to nearest breeding sites. Structural parameters, reported to play an important role for habitat choice in the Roller, were measured within a predetermined range of 25 m around all perches. Within this distance range, ca. 85 % of all hunting strikes from perches could be observed. The use of 50 m power line sections and wooden poles for perching was negatively related to the distance to nearest breeding sites, particularly during breeding season. Furthermore, the number of hunting Rollers was negatively affected by decreasing distance to settlements during breeding and post-breeding seasons in both artificial perch types. During breeding season, the attractiveness of power line sections as perches for hunting Rollers significantly increased with increasing meadow area, most likely caused by the high abundance of suitable prey (with body size >10 mm) in this habitat type. In contradiction, the proportion of maize area proved to be an important explanatory variable for perch use in the post-breeding season by negatively affecting foraging habitat quality. An increasing habitat diversity and/or habitat edge density improved perch attractiveness for hunting Rollers during breeding season (wooden poles) and post-breeding season (power line sections: 2002+2004; wooden poles). Future conservation plans aiming to protect remaining Roller populations in Central Europe should consider that ongoing loss of meadows, the decline of habitat heterogeneity due to land consolidation and agricultural intensification, in combination with an uncontrolled rural development, represent crucial threats for this highly endangered species.