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Jenny, D.

Bestandsentwicklung und Bruterfolg des Uhus Bubo bubo im Engadin.

2011

108

233–250

Key words
(von 1994 bis 2006 vergeben)

Bestand, Revier, Brut, Verbreitung, Paar

Schlagwort_Vogelart
(wissenschaftlich)

Bubo bubo

Schlagwort_Vogelart
(deutsch)

Uhu

Europa, Schweiz, Graubünden, Oberengadin, Bergell, Inn, Alpen

deutsch

Abhandlung

Population trend and reproduction of the Eurasian Eagle-Owl Bubo bubo in the Engadine. – In the Engadine valley between Maloja and Susch (Grisons) nine territories of the Eurasian Eagle-Owl were occupied in at least one year between 2005 and 2010. This corresponds approximately to a population density as noted by Haller (1978a) in the 1970s. The average distance between the eyries was 6.9 (3.6–11.7) km. In the Lower Engadine below Susch the population density was lower with an average distance of 10.8 (7.4–14.1) km. It was also lower compared to the results found by Haller (1978a) in this part of the Engadine. The occupation of the territories by Eagle Owl pairs was lower than in the 1970s and 1990s. 61 % of the controlled territories were occupied by pairs (Haller 1978a: at least 86 %). The proportion of territories occupied only by single owls was higher (24 %) than in the 1970s. Below Susch only two of seven former pairs could be confirmed. Overall, in the entire Engadine 11 of 17 known territories were found occupied, representing a drop of at least 25 %. Reproduction rate was 0.88 young per pair and year in the main study area (Maloja to Susch), the brood size was 1.61 fledged young per successful brood. In one case, a pair raised four young. The proportion of non-breeding pairs was relatively high with 21–36 %. Breeding failures were comparatively rare. As a consequence, breeding success was relatively high (72–90 % of all broods successful). During the study period 11 dead Eagle Owls were found in the Engadine, which corresponds to a rate of 0.18 birds per 10 km and year. This is less than in the past and indicates a decrease of the population. Most birds were victims of accidents, mainly of railway transport, followed by electrocution and road transport. The reduced number of occupied territories and the high turnover of territory occupancy reflects a low recruitment rate which is mainly caused by the high mortality due to accidents. But apart from technical infrastructure as a source of accidents habitat quality in the Engadine still appears to be good for the Eagle Owl. Considering the high altitude, breeding success and population density are above average.