Nest-site selection and niche partitioning among the Great Spotted Woodpecker Dendrocopos major and Middle Spotted Woodpecker Dendrocopos medius in riverine forest of Central Europe

Abstract

We studied nest-site selection of the Great- and Middle Spotted Woodpecker inhabiting the riverine forest remnants of Central Poland. In addition to nest tree characteristics and location in relation to edge proximity, a comparison between nesting and random sites within the woodpeckers' territories allowed a study of the importance of stand structure on nest tree selection. Unlike the Great Spotted Woodpecker, we found that the Middle Spotted Woodpecker showed an affinity to nest near forest edges. Both species excavated nest holes within trees with a diameter at breast height larger than the diameter of available trees suitable for hole-excavation. Trees with the presence of former woodpecker holes, polyporous fungi and limb holes were highly selected, with nest chambers commonly built in dead parts of the trees (74% and 90% of nests of Great- and Middle Spotted Woodpeckers, respectively). Both the Great- and Middle Spotted Woodpeckers nested more often in trunks than in limbs, with the former species favouring live oaks and alders and the latter snags. Vegetation immediately surrounding nest trees had probably a low influence on species nest-site selection. The nest tree was, in the majority of cases, the only tree suitable for hole-excavation in the nest site. Our results suggest that gap-phase dynamics and the presence of old and dead deciduous standing trees are key components of habitat quality for breeding woodpeckers, particularly for the declining Middle Spotted Woodpecker.