LAUSR

Abstract Tree cavities are an essential requirement for reproduction and survival of secondary cavity nesters. Little is known, however, about how cavity distribution in space and time may limit their use during and outside of the breeding season. Using long-term (17 yr) data on the use of nest-boxes resembling tree cavities by individually marked Eurasian pygmy owls Glaucidium passerinum, we compared the habitat and the distances among the nest-boxes used during two different seasons. We found that pygmy owls are more demanding in their requirements for breeding than for food-hoarding habitat, as the habitat surrounding the nesting sites had a higher proportion and biomass of coniferous forests, especially spruce, and nesting sites were farther from houses than food-hoarding sites. Pygmy owls mainly used different nest-boxes for nesting and food-hoarding and they also used different nest-boxes in different years. The distance between the nest site and food-hoarding sites was longer when the main food availability (voles) was low than when it was high. The distance was also longer in females than in males, probably indicating that females need to move further to find suitable hunting areas. In conclusion, these results highlight the importance of spruce forests as a nesting habitat of pygmy owls, and the need of several tree cavities within their home range. Forest management should secure a sufficient supply of these resources at the scale of pygmy owl home ranges.