Nest-tree and nest-stand characteristics of forest-dwelling raptors in east-central Estonia: implications for forest management and conservation

I studied 423 nests of six raptor species in east-central Estonia to (1) distinguish the essential features of the nest sites, (2) link the nest-tree and nest-stand characteristics, and (3) explore whether the availability of potential nest trees and stands limits raptor populations in managed forest landscapes. Aquila pomarina was the only species having distinct preferences for a few site types, while Accipiter gentilis and Falco subbuteo selected stands according to composition rather than site type. Coniferous trees, particularly spruce, were greatly favoured for nest-building by all species, probably due to better protective cover. Size of the nest tree was more important than its age; though on poor soils, nest trees were both older and smaller. A. gentilis, A. pomarina, and Buteo buteo appeared to be most prone to the lack of potential nest trees in managed forests, e.g. stands < 80 years old were generally inhabitable only if these contained older trees. Green-tree retention could greatly add nest sites for these raptors in managed forests. However, nest-site selectivity did not correlate with the population sizes of the six species, suggesting that nest-sites were not the main limiting factor for them.