Internet photography forums as sources of avian dietary data: bird diets in Continental Portugal

Knowing animal diets is key ecological information, required for understanding the dynamics of ecosystems as a whole, as well as the ecology of individual species. However, for many species/regions such information is not available. Here I explore the potential use of internet photography forums to describe the diet composition of birds by analysing photographs posted on the “Aves de Portugal Continental” Facebook page. A total of 909 photographs were found to show identifiable food items being taken by 144 different avian species. These included 78 regularly occurring species for which there were no available dietary data for Portugal according to Catry et al. (2010). The photographs were obtained
in 262 different locations, covering all the 18 districts of Continental Portugal. They exhibited a total of 206 different food item categories, their taxonomic rank ranging from species (n=97) to class (n=3), as well as some non-taxonomic groupings such as unidentified berry or human refuse. The avian species with the most dietary information were European Bee eater Meropsapiaster (n=68), Osprey Pandion haliaetus (n=59) and Common Kingfisher Alcedo atthis (n=40). Although this type of data are affected by several biases, namely a geographic bias in favour of areas closer to human settlements and human-altered habitats, and a possible bias favouring larger food items that are more easily identifiable in photographs, it could provide an invaluable source of avian dietary data. In the future, these data could be gathered through an open web-enabled platform which would include photographers and biologists who would provide identifications of the food items being taken.