Reaktion der Waldohreule Asio otus auf Klangattrappen – Konsequenzen für Bestandsaufnahmen

From 1989 to 2010, territories of the Long-eared Owl were counted on 27.5 km^² of an intensively cultivated landscape in central Switzerland. For a better detection of the territories sound imitations (imitation of the wing-clapping and playback recordings of male mate calls) were used. The reaction of the owls on these sound imitations was systematically recorded. The observation probability of owls from early February until the end of May was 28,2 % when no sound imitations were used, but 52.4% when imitations were applied. It increased slightly but significantly within this period of time. 53.8% of the Long-eared Owls observed during the mating season called and displayed spontaneous, 11.4% of the owls got provoked by the clapping and 34.8% by the recorder-calls. Begging chicks were observed from mid-May until early September. The mean probability to detect chicks in a territory was 43.0% and did not depend on date. The use of playback and imitations at censuses of the Long-eared Owl is recommended. During mate season at least two surveys are necessary, followed by at least two, better three, further ones during the period of chick rearing. It is also strongly recommended to record all negative observations. With such negative observations, the observation probability can be included in dynamic site-occupancy-models to estimate territory numbers.