The Ural Owl Strix uralensis meets its westernmost distribution in Hedmark County, southeast Norway. Since 1979 we have provided the species with nest boxes in this region. A total of 80 nest boxes were put out in prime Ural Owl habitat, starting with 9 in 1979, 18 in 1982 and 53 in 1985. Two more nest boxes put up by others, and four made by ourselves, were later added, giving a total 86 nest-box localities. The nest boxes were checked up to 2004, when 28 nest boxes were moved to western (n = 8) and central (n = 20) Sweden. We have analysed the results for 25 seasons from 1980 to 2004. For comparison, the results for the 20 nest boxes in central Sweden for the seasons 2005–07 have been included. The Norwegian nest boxes offered a total of 1429 nest-box years. Since all boxes were not inspected each year, the total number of observation-years was 847 (59.3%). Ural Owls only used 4 nest boxes for breeding, occupied for the first time 1, 1, 1 and 10 years respectively after the boxes were put up. The four boxes were used for a total of 19 breedings. In central Sweden, 9 out of 20 nest boxes were used by Ural Owls for breeding (n = 6) or breeding initiations (n = 3), for a total use of 8 of 56 nest-box years. The Ural Owl nest-box use in Norway (1.3% of nest-box years) is very low compared to central Sweden (14.3% of nest-box years). Telemetry studies of Ural Owl hunting behaviour in 1989–90 (unpubl.) showed that the nest boxes were indeed placed in prime Ural Owl habitat. Despite this, there was no increase in Ural Owl nest-box breeding in Norway during the study period. We conclude that Ural Owls are not limited by nest sites at the species' westernmost borderline and hypothesize that food availability during winter is a more likely factor limiting the species.
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