EN
The study covered woodland area of 22.5 km² (Fig. 1), 13 km south of the city of Poznań. The old tree stands were dominated by Scots pines with an admixture of oaks. In the period February-May 1977 and 1978, 7-8 night censuses were carried out in plots: "Rosnówko" (5.7 km², 96% of wooded area) and "Jeziory" (9.6 km², 87%). In the period January-May 1979 and 1980, 18-19 censuses were carried out in the plot "Wiry" (10.7 km², 93%). A modified mapping method, with vocal stimulation, was applied to determine the density of Strix aluco. In the "Wiry" plot territorial boundaries were delimited. Particular males were recognized by their individual display-call differences. Strix aiuco density varied from 5.5 to 14.9 pairs/10km² of forest (Table 1). In the "Wiry" plot the density was almost twice lower than in other plots, probably due to habitat poverty and a small proportion of broad-leaved trees in stands. The territory pattern varied from year to year (Figs. 2, 3, 4). Territory size ranged from 30 to 93 ha (x̅ = 61 ha, N = 11). A considerable year to year lability was found. Single male and females also kept permanent territories.