Overview of occurrence of the Short-eared Owl Asio flammeus between 1995 and 2015 in Slovenia and its probable breeding in irruptive year 2008

Abstract Between 1995 and 2015 the number of records of Short-eared Owl Asio flammeus in Slovenia increased drastically, especially after 2007, but the species occurred regularly every year since 2002. Before that, the Short-eared Owl was regarded as a very rare migrant in Slovenia. Most of the observations were from wintering and migration periods, and the most important areas for the species in Slovenia were Ljubljansko barje, Lake Cerknica, surroundings of the water reservoir Medvedce and coastal wetlands. In 2008 and 2013 the Short-eared Owl occurred in large numbers, and these years were regarded as irruptive. Flocks of 2 to 8 birds were observed. At Ljubljansko barje, increased numbers of observed Short-eared Owls coincided with a large population of small mammals (species of the genus Apodemus and Microtus) and poor snow cover in 2008, and at least three communal roost sites were found that year. In the irruptive year 2013 there was a greater number of Short-eared Owls observed at the Medvedce water reservoir. On the plain at Lesce near the village of Smokuč an injured second year female was found at the end of March 2008 with a developing brood patch in its initial stage. It is likely that the female attempted to nest, which confirms the status of the species as occasional breeder in Slovenia. The last confirmed breeding in Slovenia was recorded in 1936 at Ljubljansko barje. In addition to local conditions (population of small mammals, snow cover) the frequency of occurrence of the Short-eared Owl in Slovenia is also affected by the population of development in the Boreal region and changes in migratory characteristics of the species in Europe. Therefore, an increase of the number of Short-eared Owls in Slovenia is expected in the future, as well as breeding attempts by this nomadic owl in seasons with high populations of small mammals and green winters, of course, if appropriate meadow habitat is still preserved.