Species richness and composition of bird assemblages along an Elevational gradient in the Eastern Alps (National Park Gesäuse, Austria)

Diploma thesis at the University of Vienna Vienna While tropical mountains have detailed studies on changes in species richness of birds along altitude gradients, quantitative information from mountains of the temperate zone, such as the Alps, is sparse. By means of point-stop counts, bird communities were recorded along an altitude gradient in the Eastern Alps to investigate changes in species richness, species composition and structure of food guilds. In addition, the importance of various biotic (vegetation structure) and abiotic (area per elevation zone) variables for changes in bird communities was tested. The study was carried out in the Gesäuse National Park (Steiermark) in the area of the southern Buchstein massif. Bird counting took place along three elevation gradients, which reached from the bottom of the Ennstal (500 m) to the Tamischbach tower (2.005 m, 2 gradients) or up to the rock massif of the Great Buchstein (1 929 m, 1 gradient). In total, 87 observation points were set up along the three elevation transects. Birds were recorded at the observation points for 10 minutes visually and acoustically on three dates between 3 April and 25 July 2006. In addition, the distance of the bird from the observation point (within or outside 50 m radius) was noted. The following habitat parameters were measured or estimated for each counting point: Height ü. NN, distribution of tree trunk diameter, maximum height of wood vegetation, tree and wood species richness and tree density. In addition, the total area of the Buchstein massif and the surface area of the southern slope were determined for each individual 100 m high zone using digital maps. In total, 40 species of breeding birds could be counted within the 50 m radii. The abundance of species did not decrease continuously with increasing altitude, but showed a plateau between 500 and 1 200 m with an average of 10 species detected per observation point. After that, a significant decrease in species richness occurred to the highest investigated locations. Except the habitat variable height ü. NN and area per elevation zone, which made the greatest contribution to explaining the changes in the bird species richness, could be found significant correlations with vegetation height, tree density, tree diameter, wood species richness and habitat diversity. A comparison of the bird species composition between observation points using Bray-Curtis similarities showed a clear effect of the vegetation structure on the species composition. Significant differences could be found between the habitat types of the forest zone and the observation points above the forest border and also between mixed and coniferous forests. Significant effects on changes in species composition could be seen in addition to the height ü. NN, for wood species diversity and vegetation height. Differences in the relative abundances of food guilds between elevation levels reflected changes in habitat structure. For example, insective stem climbers disappeared above the forest boundary. Individual numbers of omnivorous and insective birds looking for food on the ground or in vegetation decreased significantly as height increases. Insective stem climbers, on the other hand, achieved their highest abundances at medium altitudes, possibly due to the intensive use of the forests of lower altitudes until more recently.