Field work for the project is carried out in the area of El Marquesado (Granada province), in the fields of La Calahorra, Aldeire and Alquife. Magpie population in these area has been intensively studied in the last 30 years, and we keep a long-term, longitudinal study running since 2006. We monitor every year the reproduction of individually marked birds in order to better understand the ecological and evolutionary interactions of brood parasites and their hosts. Our study area is a patchy mosaic of groves of almond and olive trees and meadows. Magpies preferentially build their nests in almond trees, and great spotted cuckoos are relatively common; they are brood parasites that use magpies and main hosts in Europe.