engleski

Population density and habitat selection of the Eagle Owl Bubo bubo in Dalmatia (Eastern Adriatic).

We estimated the Eagle Owl population in Croatia to be 1000 - 1500 breeding pairs. The estimation is rough, based on numerous, but mainly unsystematically collected records. The majority of population breeds in the Mediterranean part of the country (Istria, Croatian Littoral, Kvarner and Dalmatia). In mountainous, heavily forested parts it is rare, while in lowland Croatia it most likely became extinct some fifty years ago. In period from 2001 to 2006 we studied population density of the Eagle Owl in Dalmatia. We used playback method to provoke Eagle owl territorial vocalization on three locations: on Dugi otok - Kornati Archipelago, islands which are about 16 km far from the mainland ; in the Nature Park Vrana Lake, the area situated along the seacoast and in the central part of National Park Krka (about 12 km inland). In addition, investigations were carried out on the small island of Ciovo (few hundred meters apart from the mainland), without the use of playback method, but the whole area was systematically searched and all active nests were found. Densities of the Eagle Owl recorded during the study ranged from 4.5 to 26 pairs/100 km2. The highest density, 26 pairs/100km2 (i.e. 22 pairs/84 km2 of researched area), found on the Dugi otok - Kornati Archipelago, is in a range of the highest breeding densities recorded in Europe. This scarcely populated archipelago where rocky pastures prevail (54%) seems to be the optimal habitat for the Eagle Owl. Although the Rabbit population size on the archipelago is very low, the vicinity of numerous breeding gull colonies which Eagle Owl exploits as well as small number of predators existing on distant islands most probably contributes to its high density. Breeding densities found in two studied areas on the mainland (Nature Park Vrana Lake and National Park Krka) were considerably lower but similar to each other (5.5 pairs/100km2 and 4.5 pairs/100km2 respectively). The habitat compositions of these two areas are similar: mosaic of pastures and bushes prevails in both areas. Relatively high density (12.5 pairs/100km2, i.e. 3 pairs/24 km2 of researched area) was found on the island of Ciovo. As this is relatively heavily populated and largely forested island (82%), the recoded density is intriguing. One explanation of the high density could be that the Eagle owls which breed on the Island hunt on the nearby mainland. However, as the settlements and forests cover the part of the Island closest to the mainland, all three pairs were forced to nest on the most distant part of the Island. Potential hunting grounds on the mainland are therefore at least 4 km far from the nests, so second possibility could be that prey availability on island itself and nearby archipelago is high.

Eagle Owl; Bubo bubo; density; habitat; Croatia

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