Substantial contribution of invertebrates to the diet of a winter seed-eater, the reed buntingEmberiza schoeniclus, wintering in a sewage farm in south-western Poland

We investigated whether the winter diet of a typical seed-eating bird is hard-wired in the context of evolutionary hypothesis for granivory. We examined the diet composition of 'a small-billed form' of the reed bunting Emberiza schoeniclus wintering in a sewage farm in south-western Poland (Central Europe), where unfrozen wastewater provides various groups of invertebrate prey. The analysis of droppings (N = 151) collected from four different feeding grounds located in reedbeds and grasslands inundated with waste-water showed the substantial contribution of invertebrates in the diet of reed buntings. Across four sample areas, the frequency of invertebrates in faecal samples ranged between 37% to 80%. In total, we identified 194 animal prey, mainly spiders Araneae (53% of all identified invertebrate prey), and several taxa of Coleoptera (43%). Among plant food (N = 8357 identified items), the most numerous were shells of weed seeds, namely Amaranthus sp. (56.8%), Urtica dioica (22.6%), and Chenopodium sp. (19.6%). Our results showed that, during winter, the reed bunting is not an obligatory seed-eater. This species may exploit both animal and plant food; hence, our results indicate that the reed buntings wintering in temperate Europe may feed more opportunistically than was previously assumed.