Importance of Orthoptera in the nestling diet of southern grey shrikes in agricultural areas
Published: Volume 57(2), December 2010. Pages 257-265.
This paper describes the nestling diet of southern grey shrikes in agricultural areas (Castronuño, Valladolid province, Spain, 41º 23’ N 05º 16’ W). A video-camera was used to record the prey used for feeding nestlings by adult southern grey shrikes of ten different nests. Nestling age varied from 5 to 13 days. The percentage of occupancy of each kind of habitat (vineyards, cereal crops, natural habitat, others) within a radius of 250 m around each nest was computed from aerial pictures. Prey availability was analysed with pitfall traps placed in three different habitats in the study area. Orthoptera were the most frequent prey (69.56%, N = 287), in particular crickets Gryllus campestris (85.5% of all Orthoptera). Vertebrates comprised 3.05% of the total prey. Orthoptera were positively selected by feeding adults in all the studied nests. Arachnida and Coleoptera were not positively selected in any of the nests and in fact were negatively selected in 50% and 90% of the nests, respectively. The percentage of feedings with Myriapoda, Hymenoptera and Dyctioptera were similar to the frequency of these prey in the pitfall traps. Myriapoda and Orthoptera were the largest prey, whereas Arachnida and Coleoptera were the smallest. Differences with previous studies from other location can be ascribed to the shrike’s adaptation to the transformation of the habitat into an agroecosystem since: (i) Orthoptera are highly abundant in vineyards, where the large number of available perches and the lack of herbaceous vegetation enable shrikes to capture them; (ii) they have a high content of proteins and water, and they probably favour a more rapid nestling growth.