Block B. (2009) Long-term research of population density and trends of Long-eared Owls Asio otus in Brandenburg, Germany. ARDEA 97 (4): 439-443

The density and reproduction of Long-eared Owls Asio otus were studied in a 5000 ha study area of Havelland, Brandenburg, Germany from 1984 through 2007. Locations of territorial Long-eared Owls were mapped from the end of January until the end of April, counts of fledged young were made from mid-May until August. Long-eared Owls nested in conifer groupings or isolated woods in the agricultural landscape. Nearly all nesting took place in nests of crows Corvidae, mainly in Scots Pine Pinus sylvestris trees. A total of 867 breeding attempts were recorded; 335 (36.6%) pairs were successful in fledging 1468 young. The reproductive output was 1.57 fledglings for all pairs that attempted to nest, and 4.31 fledglings per successful pair. Average population density for the 24 years was 72.7 breeding pair/100 km² (range 40–118 breeding pair/100 km2). For the time frame of 1984–2007 there was no trend in the number of breeding pairs or in the number of young fledged. After 1990, when conservation-focused farming in the nature reserve began, the number of young fledged increased significantly. Grassland management is considered a principal conservation measure for Long-eared Owls in Brandenburg, Germany.