Recognizability of different food types in faeces and in alimentary flushes of Sylvia warblers

The efficiency of the analysis of faeces and flushes of the digestive tract was examined by feeding captive Garden Warblers Sylvia borin and Blackcaps S. atricapilla with different food types (arthropods, fruits). Faecal analysis underestimated aphids; the analysis of flushes overestimated beetles and underestimated aphids and fruits. Correction factors to remove these biases are given. Flushing free-living birds showed no noticeable effect on recapture rates and body mass. Methods of calculating the number of prey items from different fragments are evaluated.