EN
The co-occurrence of Redbacked Shrikes (Lanius collurio) and Barred Warblers (Sylvia nisoria) was monitored during the years 1999–2003 at 343 ha of agricultural landscape of eastern Poland. Each year 25–31 pairs of Red-backed Shrikes and 3–8 pairs of Barred Warblers were nesting. In total, during five seasons, shrikes were nesting in the vicinity (within 50 m from the centre of the Barred Warbler territory) of 22 out of 24 (92%) warbler territories. The breeding success of the pairs nesting close to Barred Warbler territories was 89%, as compared with 61% for the remaining pairs and it was statistically significant. No difference was found in the clutch size between Redbacked Shrikes nesting close to Barred Warblers and far from them, but statistically significant difference was found in numbers of fledglings between them. The present results imply that close nesting of these two species reduces the risk of nest predation. This may be due to the aggression of Barrred Warblers towards potential predators, as this species actively attacks predators near the nest.