Season-dependent diet composition and habitat use of Red-backed Shrikes Lanius collurio in SW Finland

Abstract

The local habitat use and diet of Red-backed Shrikes were studied in a main study area of 1.4 km2 in SW Finland. Based on pellets (n=688), Carabidae beetles constituted 29.1% of the prey (n=3,388) and Apidae (especially bumble bees), 18.3%. The rest was mainly representative of other beetle families (21.6%), other hymenopterons (12.6%) and Orthoptera (8.3%). In the diet, beetles decreased whereas Apidae and Orthoptera increased as the season progressed, reflecting alterations in abundance and vegetation-dependent availability of these prey. Breeding shrikes were found in natural unmowed meadows (n=14 pairs and in areas created by forestry (n=11). The start of incubation (average June 9th), territory size, breeding success (3.4-3.7 large nestlings/pair) and the abundance and percentage of diet of the main prey were similar in both habitats. However, in the post-breeding season, shrikes avoided habitats created by forestry but showed a particular preference for meadows. This was, in part, related to a high abundance of Orthoptera insects in this habitat type, which was supported by diet analyses. In addition, factors minimizing the risk of predation, i.e. the openness of meadows, may have contributed to the observed habitat selection. The role of suitable post-breeding habitats is discussed based on the observed population decline of Red-backed Shrikes.