Trophic ecology of the Southern Grey Shrike (Lanius meridionalis) in insular environments: the influence of altitude and seasonality

The seasonal diet and prey selection of the Southern Grey Shrike (Lanius meridionalis) was studied in two different insular habitats: shrub environments of the Canary Islands in coastal and high mountain zones. We measured, in each season, food availability and prey size in order to determine prey size selection of shrikes along an altitudinal gradient. Moreover, we compared the diet patterns observed with those documented on the continent, to determine if Southern Grey Shrikes in the islands’ high mountain zone (which has a continental climate) showed seasonal diet variation similar to those in northern continental areas. We analysed a total of 1,139 shrike pellets collected in 1 year and identified 10,179 prey items. Numerically arthropods (91%), and in terms of biomass lizards (70%) were the main prey consumed by the shrikes. The proportions of the main prey items differed significantly between seasons and habitats. Diet in the coastal areas was less variable than in the high mountain zone. The greater seasonal climatic variation in the high mountain zone was associated with diet patterns similar to those found in some northern continental areas, such as the Iberian Peninsula and southern France. Finally, shrikes selected the largest prey in the high mountain habitat. This suggests that foraging behaviour in this species is related to climatic conditions, as the biggest and most profitable prey were consumed in the most harsh habitats.