NESTLING DIET OF THE SPOTLESS STARLING STURNUS UNICOLOR AND THE EUROPEAN STARLING STURNUS-VULGARIS IN A SYMPATRIC BREEDING AREA

The diet of nestlings of Spotless and European Starlings (Sturnus unic olor and S. vulgaris respectively) was analysed in a sympatric area in north-eastern Spain. Results showed that the nestlings were fed mostl y with insects (94% of prey in the Spotless Starling and 95% in the Eu ropean Starling); some of the Arthropoda and Gasteropoda were also rec orded. The Syrphidae (Diptera) and Chrysomelidae (Coleoptera) constitu ted the main food, especially in the Spotless Starling. The Scarabeida e (Coleoptera) and the Lepidoptera were the most important secondary p rey for the Spotless Starling, whereas secondary prey items for the Eu ropean Starling were the Araneida, the Acrididae (Orthoptera) and the Lepidoptera. These data agree with the general results obtained from o ther study areas, but differed because of the high frequency of the Di ptera in the diet of the Spotless Starling and the total absence of th e Lumbricidae in the diet of the European Starling in our study area. Significant differences were recorded in the diet of the nestlings of the two species, although the two weeks difference in the breeding phe nology of the two species could explain these differences. Probably fo r the same reason, significant differences between broods were also re corded for the Spotless Starling. Nevertheless, the width of the diet niche did not show any significant difference between the two species at either the individual or population levels. Furthermore, the result s of the Morisita Index indicate a very high niche overlap, suggesting that both species exploited, to a large extent, the same food sources .