Seasonal and annual changes in the diet of the Red-backed Shrike Lanius collurio in farmland of Eastern Poland

The aim of the study was to identify differences in diet composition of the Red-backed Shrike during the breeding period and between years related to habitat diversity of territories. The study was conducted in 1999-2003 in extensive farmland of Eastern Poland. The diet composition the Red-backed Shrike was analysed based on examination of animal remains in pellets found under nests and places where the birds often stayed. The material was divided into two groups: pellets collected in territories with predominantly arable land and others with predominantly grasslands (meadows and pastures). In territories with the prevalence of arable land the proportion of Hymenoptera in the Red-backed Shrike diet increased, and of Coleoptera decreased, with the progress of the season. A corresponding pattern was not observed in territories comprising grasslands. Territories of the Redbacked Shrike located in the same places in two years did not differ in the proportions of Coleoptera and Hymenoptera in a birds' diet. This can be an evidence of a food stability of Red-backed Shrike's territories in consecutive years and of dietary preferences of this species. Grasslands supported a greater abundance and variety of invertebrates in comparison with arable land. Thus, actual food preferences of Red-backed Shrikes in grassland territories could be causing the lack of a relation between season and the proportion of a given taxon in the diet. Thus, the occurrence of feeding preferences in sites of restricted feeding conditions may not entirely reflect actual food selectivity of the species.