Comparison of methods for diet analysis and prey preference: a case study on the Red-backed Shrike Lanius collurio

Abstract

I studied diet composition and prey preferences of the Red-backed Shrike (Lanius collurio) in an extensive agricultural landscape in the eastern part of Poland. The diet composition of the Red-backed Shrike was described based on the analysis of animal remains in pellets (n = 968 prey items), larders (n = 115), butchering points (n = 1180) and nests (n = 79). Remains from all methods combined showed that Insecta predominated in the diet, comprising 98.9% of all prey items. Coleoptera prevailed decidedly (83.6%), followed by Hymenoptera (8.0%), Orthoptera (3.8%), Heteroptera (1.5%) and Diptera (1.1%). The proportions of the taxa in the diet of the Red-backed Shrike differed between the methods of food analysis, mainly with respect to Hymenopterans and Orthopterans. I found differences in the proportion of taxa between nests and butchering points, nests and larders and between animal remains in pellets and larders. I studied preference by comparing the proportions of potential prey of the Red-backed Shrike with the proportion of these prey items in their food. Red-backed Shrikes prefer beetles and Hymenopterans, and avoid Dipterans and Arachnids. The level of this preference differed depending on the methods of food analysis used.