The eagle owl Bubo bubo (Aves: Strigidae) in the Eastern Adriatic (Croatia): the study case of a high-density insular population

Abstract

The Croatian population of the eagle owl Bubo bubo (Linnaeus, 1758) is estimated at 800–1200 breeding pairs with the majority of population breeding in the Mediterranean region, along the eastern Adriatic coast. The main aims of this work were two-fold: (1) to determine the eagle owl territorial densities in the central part of Mediterranean Croatia; and (2) to examine landscape composition and configuration of the study plots and consider possible reasons for differences in recorded densities. The abundance of the eagle owl was surveyed from 2001 to 2006 within three plots of similar size (a total survey area of 246 km2): two plots were on the mainland and one on the archipelago at about 16 km from the coast. The playback method was used to stimulate eagle owl territorial behaviour and to determine the locations of their territories. Territorial densities ranged from 4.5 to 26.2 pairs/100 km2, with the highest density being recorded on islands. We suggest that this high density is a result of good foraging conditions, especially year-round availability and high abundance of the yellow-legged gull Larus michahellis J. F. Naumann, 1840 and the brown rat Rattus rattus (Linnaeus, 1758), together with low risk of human-induced mortality.