Interspecific Relationships between Some Insectivorous Passerine Species, Illustrated by Their Diet during Spring Migration

Abstract

Arthropods were the most important source of food for the investigated species [Phylloscopus collybita, P. trochilus, Sylvia curruca, S. communis, S. atricapilla and S. borin] during their spring migation. The species showed great flexibility with regard to different groups of prey in successive periods within the same migratory season, and from one year to the next. The overlap in composition of prey taken and in the size of the prey animals is calculated for the species. There was a large variation in the size of both overlaps from period to period within the same year (overlap in prey composition) and from year to year (overlap in prey composition and overlap in prey size). This variation is explained as arising from variations in intensity of interspecific competition. Segregation into different prey groups during increased competition may be due to segregation into different microhabitats and/or different types of foraging behavior.