Diet plasticity in blackcap (Sylvia atricapilla): The ability to overcome nutritional constraints imposed by agricultural intensification

We studied the consequences of agricultural intensification on the diet, nu tritive balance, and body condition of an avian frugivore (blackcap, Sylvia atricapilla) that overwinters in southern Spain, and analysed dietary plas ticity as an ability to overcome the effects of agricultural intensificatio n. We considered two habitats with very different levels of land-use: Medit erranean shrublands dominated by wild olive trees, and highly managed olive orchards. We partitioned the diet into four basic components: olive fruits , non-olive fruits, arthropods, and non-fruit plant matter. Availability of these resources, which influenced diet composition and body mass, differed among habitats and reflected the degree of human land-use. Hedges in olive orchards increased the local fruit diversity, making the diet and body mas s in olive orchards more similar to that of less altered habitats. Based on diet composition analysis in relation to energy, protein, and mineral inta ke, we suggest that blackcaps wintering in olive orchards select non-fruit plant matter (a rare item in other habitats) so as to balance their energy, protein, and mineral intakes. This is necessary because of the scarcity of resources other than olives in orchards. Moreover, such deficiency probabl y results in higher exploitation costs, which in turn may affect the birds' physical condition. Remarkably, blackcap shows a high dietary plasticity a mong habitats during the autumn-winter period in southern Spain, which seem s to help this species reside for part of the year in a large man-made regi on.