Consistency and overlap of the diet of seven passerine trans-saharian migrants during spring stopover at two mediterranean sites

Abstract

The diet of seven passerine trans-saharian migrant species was analysed by means of faecal analysis during their spring passage at an Italian stopover site (Sardinia). Here birds co-occur at high densities in a mostly unknown and unpredictable environment. This allows us to analyse the consistency of the species’ feeding pattern in different weather conditions (Capo Caccia 1990–1991) and sites (S. Pietro 1992). The diets of the seven species are mainly composed of insects, they are consistent over the three study years and they reflect the birds’ foraging behaviour. The pied flycatcher and the redstart (mostly ants), the garden warbler and whitethroat (varied diets including Formicidae, Coleoptera, Apbidoidea, berries), and the willow and the wood warblers (mostly Apbidoidea) are similar or closely related, and form three species pairs with very similar diets. The spotted flycatcher is similar to the first pair, but with a higher proportion of Diptera and Hymenoptera (non Formicidae). Since species that are similar or closely related have also a very similar diet composition, this cannot be a means by which they can avoid competition. The existence of competition for food and possible ways to test it are also discussed. © 1996 Taylor & Francis Group, LLC.