Nestling diet of the Spotless Starling Sturnus unicolor and the European Starling Sturnus vulgaris in a sympatric breeding area

Abstract

The diet of nestlings ofSpotless and European Starlings (Sturnus unicolor and S. vulgaris respectively) was analysed in asympatric area in north-eastern Spain. Results showed that the nestlings were fed mostly with insects (94% of prey in the Spotless Starling and 95% in the European Starling); some of the Arthropoda and Gasteropoda were also recorded. The Syrphidae (Diptera) and Chrysomelidae (Coleoptera) constituted the main food, especially in the Spotless Starling . The Scarabeidae (Coleoptera) and the Lepidoptera were the most important secondary prey for the Spotless Starling, whereas secondary prey items for the European Starling were the Araneida, the Acrididae (Orthoptera) and the Lepidoptera. These data agree with the general results obtained from other study areas, but differed because of the high frequency of the Diptera in the diet of the Spotless Starling and the total absence of the 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 phenology of the two species could explain these differences. Probably for the same reason, significant differences between broods were also recorded 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 results of the Morisita Index indicate a very high niche overlap, suggesting that both species exploited, to a large extent, the same food sources.