Lõhmus, A., Kinks, R. and Soon, M. 2010. The Importance of Dead-Wood Supply for Woodpeckers in Estonia.  Baltic Forestry 16 (1): 76-86

We explored which species of woodpeckers depend on the supply of standing dead trees (snags) in Estonia and how that dependence relates to their invertebrate prey base. In a 900-km2 area in east-central Estonia, we described the snag supply within a radius of 600 m around 73 nests of six woodpecker species and in 30 random transects representing the available forest landscape. We modelled woodpecker habitat preferences as differences between the snag supply around their nests and in random transects, analysed the incidence of woodpecker foraging signs in terms of dead-wood characteristics, and estimated the abundance of arthropods in bark samples collected from snags in late winter. The results confirmed the division of woodpeckers into ‘snag specialist’ and generalist species. Characteristically, the abundant snag supply in the nesting territories of the three specialised species – White-backed Woodpecker (Dendrocopos leucotos), Lesser Spotted Woodpecker (D. minor) and Three-toed Woodpecker (Picoides tridactylus) – included many alders and Norway spruces and few Scots pines, which generally followed the frequency of use and arthropod abundance in these trees. The scarcity of arthropods in the bark samples from birch coincided with a low frequency of foraging signs on its trunks; however, birch was not avoided around the nests and may host important prey base in its abundant fungal fruit-bodies. Larger snags tended to have more arthropods per unit of bark area but their importance for woodpeckers was not clear. We concur with previous suggestions that the requirements of specialised woodpeckers can be used for deriving tentative targets of snag-retention. In this study, their nesting probability increased from 25% to 75% when snag densities (≥5 cm diameter, ≥0.5 m height; pine snags excluded) increased from 100 to 200 trunks per hectare. However, snag management should be spatially explicit, because such levels can hardly be sustained all over the landscape, and also consider at least epixylic fungi and specific insects, which require different types of snags than woodpeckers.

Key words: dead wood, forest management, habitat selection, snag, woodpecker