Seasonal diet of an insular endemic population of Southern Grey Shrike Lanius meridionalis koenigi on tenerife, Canary Islands

摘要

The diet and prey selection of the Southern Grey Shrike (Lanius meridionalis koenigi) was studied in one of the scarce insular environments where it is present, the xeric coastal area of Tenerife (Canary Islands). The main aim of this study was to compare the general trophic patterns with respect to continental populations of Northern Grey Shrike (Lanius excubitor) and Southern Grey Shrike. The material analysed consisted in 440 pellets collected during the four seasons of the year in the period April 2003-March 2004. A total of 5,112 prey items were identified, 85.4% corresponding to beetles (mainly Curculionidae and Tenebrionidae) and the rest consisted of other arthropods and vertebrates. Biomass mainly constituted of vertebrates, especially lizards (64.0%). Slight seasonal variations in diet were recorded, beetles and lizards being highly consumed in all seasons. A positive selection of some beetles, non-Formicidae Hymenoptera and Orthoptera (Schistocerca gregaria) was observed. The data obtained in the present study confirms the hypothesis of how the Southern Grey Shrike relies on cold-blooded prey in hot climate (e.g. south of France), while the Great Grey Shrike mainly relies on warm-blooded prey in cold climate (e.g. Scandinavian Peninsula). The importance of lizards in the diet of this insular shrike population could be related to three different ecological factors: (1) the high abundance of these ectotherm vertebrates in island environments, (2) the higher effectiveness of predation and (3) lower investment of energy to capture them.