Dietary selectivity mediates niche overlap and interspecific competition in a reedbed warbler community in southern Europe

Sympatric species are expected to use resources differently along one or more ecological dimensions. This can be complex when there is partial separation along multiple dimensions, such as where bird species exhibit similarities in habitat use and diet. We used DNA metabarcoding to examine the diet of three sympatric warblers: the migratory Eurasian Reed Warbler Acrocephalus scirpaceus and Great Reed Warbler Acrocephalus arundinaceus, and the resident Cetti's Warbler Cettia cetti , breeding in reedbeds in Catalonia, Spain. Although the diets of the three species partially overlapped, each consumed some distinct prey taxa, and/or key species at differing frequencies. Compared to the Eurasian Reed Warbler, the Great Reed Warbler consumed a greater proportion of larger prey, while Cetti's Warbler consumed a greater proportion of terrestrial species. Together, these results indicate a degree of dietary niche separation between warbler species, via species‐specific prey selectivity, which may explain their coexistence in Catalonian reedbeds. Our findings have implications for understanding future competitive pressure and coexistence of reedbed warblers under the dual, connected threats of climate change and global invertebrate decline.