Samara Oblast showed the owls taking up residence in boxes at an average distance of ; against which the average distance of all installed boxes was . Nest characteristics Potential nesting sites include large natural holes in trees, cavities left by large branch that have broken off, hollow trunks where canopies have been broken off (or "chimney stacks"), fissures or holes in cliffs or between rocks and holes in buildings. Tree crags and stumps used preferentially in central and eastern Europe are quite often common birch (Fagus sylvatica) or occasionally common oak (Quercus robur). Also Ural owls may regularly use stick nests of larger birds such as various accipitrids, in particular those built by goshawks and buzzards, as well as black stork (Ciconia nigra) nests, common raven (Corvus corax) nests and squirrel dreys, though dreys and nests of smaller birds such as sparrowhawks and crows may present risk of regularly collapsing as they may be overly small and perhaps flimsily built. A highly unusual nest site in terms of regional habitat was recorded in Slovakia, in the Východoslovenská Plains, a lowland floodplain, within an old buzzard nest. Nest can be in the vicinity of small towns, as was recorded in southern Sakhalin, so long as appropriate habitat and prey access is available in the region. In one case in Norway, a Ural owl utilized a hole in a common aspen (Populus tremula) in the same tree where common mergansers (Mergus merganser) were using a different hole. In several parts of their range they may make use of nest boxes, with the trend of nest box placement beginning and being perhaps most persistently used in Fennoscandia. Large nest boxes with an opening of about in diameter are preferred by the species. Elsewhere, about 29% of nest boxes set out in Slovenia are known to have been used. In Russia’s Altai Krai, Biya River area between 2010 and 2012, 15.2-48.9% of nest boxes that were erected were used with annual variation explainable by cycles of primary food sources. In Samara Oblast of 74 nest boxes set in 4 study plots by 2009, 41.9% were used by Ural owls (with about 14.9% used by various other animals). In Samara, about 20.6% of Ural owls pairs in the study block still used natural nest sites despite the availability of nest boxes. Nearby to the prior site, in the woodlands outside of Biysk of the