Food habits of the stone marten (Martes foina) (Mammalia: Carnivora) in plain areas of Northern Italy prior to pine marten (M. martes) spreading

In the two last decades, the pine marten Martes martes has expanded in the River Po plain, causing the displacement of the stone marten M. foina from residual wooded areas. As a high degree of food niche overlap can favour exploitative competition and information about stone marten diet in Northern Italy was scarce, we analysed a sample of 181 stone marten faeces collected, prior to pine marten expansion (19971998), in the hay-lofts of farms located in the central plain of the River Po. Results were expressed in terms of both frequency of occurrence and mean percent volume, while seasonal variation was assessed by Compositional Analysis. The availability of small mammals was assessed by the analysis of 116 barn- and tawny owl pellets. The bulk of stone marten diet was made up of four main items in equal parts: fruit, birds, lagomorphs and small rodents. Seasonal variation occurred for fruits, which were eaten more in the ripening season, and birds, which were less preyed upon in spring/summer. Insectivores were avoided, while rodents were preyed upon according to their availability, except for Apodemus sylvaticus, which was avoided. Anthropogenic food was scarcely used, although the farms were close to villages. The sharply higher frequency of occurrence of birds with respect to other Mediterranean areas may be related to the reduced availability of small rodents in intensively cultivated areas. The stone marten was confirmed to be an opportunistic predator, able to cope with human-induced variation in the availability of food resources. Nonetheless, in heavily man-altered habitats, the reduced availability of food resources may enhance the effects of competition for food with the expanding pine marten. Further studies are needed in areas of sympatry, as local differences in food availability may influence both predators' response to competition.