HAWK OWLS IN FENNOSCANDIA - POPULATION FLUCTUATIONS, EFFECTS OF MODERN FORESTRY, AND RECOMMENDATIONS ON IMPROVING FORAGING HABITATS

Hawk Owls (Surnia ulula) are diurnal raptors found across the northern hemisphere in open boreal forest habitats. In Fennoscandia (Finland, Sweden and Norway), their diet consists mainly of microtine rodents. T he population densities of these microtines usually peak every 3-4 yr and fluctuations are geographically asynchronous. Hawk Owls respond by concentrating and breeding where and when microtine abundance is high . The resulting strong temporal and spatial short-term variation in Ha wk Owl density in Fennoscandia makes any long-term population trends d ifficult to detect. Hawk Owls locate their prey visually from elevated perches and need ample space for long-range scanning and attack. Ther efore, harvesting old forest by clear-cutting is believed to benefit t he Hawk Owl. However, this may depend on the values of several variabl es, such as clear-cut size and shape, height of trees in clear-cut edg es, density and height of residual trees left in clear-cuts after logg ing, type and extent of ground cover and prey species composition and abundance in clear-cuts compared to old forest. Based on data on the H awk Owl's attack range, recommendations are made for spacing of residu al trees as hunting perches. No single habitat in Fennoscandian forest s seems to be superior for foraging Hawk Owls throughout the year and the effects of modern forestry on Hawk Owls, although probably positiv e, at present are difficult to predict.