EN
The survey aimed to find potential breeding sites of the Boreal Owl Aegolius funereus in the Bydgoszcz Forest (N Poland) was conducted in 2019. Based on promising survey results from 2019, a more detailed survey was performed in 2020. A total of 15 calling males were found on three sample plots (30 km² each), and two males in their immediate vicinity. The mean male density was estimated at 2.3, 1.7 and 1.0 territory/10 km², respectively). In total, 9 hollows occupied during the day were detected. At least three of them were nest holes; a female incubating eggs was recorded inside. Only in one case 3 owlets left the nest. The occupied hollows were found in the trunks of Scots Pines aged between 113 and 198 years, in forest stands of various structures. The area should be monitored in the future to establish the population trend. Potential dangers may be limited by the designation of protection zones in the vicinity of nesting trees.