NESTLING DIET VARIATION IN AN INSULAR MEDITERRANEAN POPULATION OF BLUE TITS PARUS-CAERULEUS - EFFECTS OF YEARS, TERRITORIES AND INDIVIDUALS

Mediterranean evergreen forests of Corsica are characterized by relati vely high species diversity of arthropods with low population densitie s. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlin gs and especially on two main components, caterpillars and spiders. Th e nestling diet was studied for two years using 8-mm cameras that auto matically took photographs of adult birds with food. The diet was comp osed of c. 50% caterpillars and c. 30% spiders. There were between-yea r and between-individual differences in these proportions. In both yea rs of the study the proportion of caterpillars declined during the cou rse of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitati on exists on Corsica, which can considerably influence life-history tr aits of the blue tit.