Food selection of wintering common cranes (Grus grus) in holm oak (Quercus ilex) dehesas in south-west Spain in a rainy season

Abstract

In the holm oak Quercus ilex dehesas of the Iberian Peninsula, several food types occur that can be selected by birds through the winter. In this framework, diet composition and diet selection of common cranes Grus grus was studied during a rainy wintering season. The winter diet of the common crane is mostly herbivorous in the holm oak dehesas of south-west Spain with <10% of items being of animal origin. Leaves and stems of sown cereal, bulbs, acorns and cereal grain are the most common vegetable food types. The diversity of the overall winter diet was similar among juveniles and among adults with and without juveniles in attendance. However, there were differences in diet composition between juvenile birds and their parents. Furthermore, the diet composition of adult cranes with juveniles in attendance was different from that of adult cranes without juveniles in attendance. Foraging abilities of juvenile cranes did not vary significantly through the winter, suggesting a low effect of experience on diet differences between age classes. Our results point toward the existence of diet differences among the three considered crane categories related with differential habitat selection by family groups. The monthly pattern of choice of each food type differed from those expected according to the monthly pattern of food availability in the study area. Cereal grain was the most preferred food type when it was available. When cereal seed germinated, cranes shifted to acorns and bulbs which were then more profitable.