Stefanie Riemer

PDF der Diplomarbeit im Hochschulschriften-Service der Universität Wien

An analysis of woodpecker community structure and habitat use at the Donauauen National Park in Eastern Austria

Many characteristics of alluvial forests (e.g. high deadwood availability, structural and species diversity) make them excellent habitat for woodpeckers. A survey of the woodpecker community was conducted in a 1,170 ha study area in floodplain forest in the Donauauen National Park (Eastern Austria) between February and April 2008. Densities of Great Spotted Woodpecker Dendrocopos major (5.98 territories/10 ha), Lesser Spotted Woodpecker D. minor (0.20-0.24 territories/10 ha), Green Woodpecker Picus viridis (0.14-0.15 territories/10 ha) and Black Woodpecker Dryocopus martius (0.06 territories/10 ha) were comparatively high, whereas Middle Spotted Woodpecker Dendrocopos medius densities (0.28 territories/10 ha) were lower than those reported for many other lowland forests. Based on abundance (Dendrocopos species) and occurrence (D. martius and P. viridis) of the species in 400 x 400 m grid squares, GLMs were performed to test for effects of (1) tree species composition and (2) structural habitat variables. The Great Spotted Woodpecker showed no distinct habitat preferences but selected older stands. Middle Spotted Woodpecker abundance could best be explained by stand age, the proportion of oak and ash, and proximity to sidearms. The Lesser Spotted Woodpecker selected softwoods (alder, willow, white poplar, hybrid poplar) and ash. Its pronounced affinity for sidearms can probably be explained by the association of softwoods with water-ways. The best predictor for the occurrence of the Green Woodpecker was forest edge density. All Green Woodpecker territories were located in less frequently inundated hardwood forest, and hybrid poplars and willows were significantly avoided by this species, possibly due to less favourable foraging opportunities (ants) in wetter habitats. The Black Woodpecker preferred forest rich in oak, maple, hybrid poplar and white poplar and was frequently registered near sidearms. Some overlap in habitat preferences was found for D. martius and D. minor, which will hardly compete with each other at a microhabitat level, and to some extent for D. major and D. medius. Nonetheless, the comparatively low densities of D. medius are probably not attributable to competition with the Great Spotted Woodpecker but rather to the low stand age (mean 54 years) and the relatively low proportion of oak (10%) in the study area. An analysis of direct observations of the Dendrocopos species and D. martius showed a significant preference for dead and dying trees by all species, although stands rich in deadwood were not preferred, possibly because at a volume of 27 m3 per ha, deadwood may not constitute a limiting factor in the study area.