Naturalized plants decrease diet similarity between an invasive bird and its most similar native species

Although invasive animals can compete with native species for resources, detrimental competition for food is seldom reported in the avian invasions literature. In temperate climates, food limitation and energetic stress are higher during winter and, thus, winter diets might reveal competition that is not apparent during the rest of the year. We compared autumn and winter diets of the invasive common waxbill (Estrilda astrild) in northwest Iberia, and of the native bird most similar to it in foraging behaviour, the European serin (Serinus serinus). Both species forage for seeds in open habitats, mostly in or around agricultural areas. We found that food preferences of the two species were substantially different when foraging on the same agricultural landscape. Contrary to the prediction that food scarcity in winter would make diets more similar, the diets of waxbills and serins diverged in winter, indicating low potential for detrimental interspecific competition. Differences in diet we...