The effect of elevation and habitat cover on nest box occupancy and diet composition of Boreal Owls Aegolius funereus

Capsule: Diet composition of Boreal Owls Aegolius funereus was not affected by habitat cover, but it changed along the elevational gradient.Aims: To assess the effect of elevation and habitat cover on nest box occupancy and diet composition of a central European population of Boreal Owls.Methods: A Boreal Owl population was studied in the Sumava Mountains, Czech Republic, at elevations from 500 to 1300m above sea level (asl), during 1984-2005.Results: Boreal Owls occupied more frequently nest boxes above 600m asl, but they did not clearly prefer any elevational band. Habitat cover did not affect the number of nesting attempts. There was also no relationship between habitat cover and diet composition. However, diet composition significantly changed along the elevational gradient. In particular, the proportion of alternative prey of Boreal Owls, i.e. birds and shrews Sorex sp., rose with increasing elevation. The proportion of voles Myodes and mice Apodemus in the diet decreased with increasing elevation. Among bird prey, the proportion of finches Fringillidae positively correlated with elevation.Conclusions: Central European Boreal Owls did not show a clear preference for any habitat cover or elevational band, but the quality of the owls' diet significantly decreased with increasing elevation.