Diet of foxes and martens in central Poland

The diet of foxes and martens was examined on the basis of the composition of their feaces (1139 and 813 portions, respectively) collected from the same area in central Poland. Although the mean density of the common vole was low in the study area, an increase in the number of these rodents was followed by a functional response of both foxes and martens. This response, however, was weaker than in the areas with a high abundance of voles. The proportion of voles in the diet was more variable in the study area than in the areas of their high densities. In the diet of foxes, three groups of food items were found in similar proportions (about 26-33% by weight): small mammals, birds, and hares. In foxes a compensatory response was found between the consumption of small mammals, on the one hand, and birds and hares, on the other. Martens consumed the same three groups of prey; but also fruits were an important component of their diet (37%). Except for small mammals preyed upon by martens throughout the year, the other food items (hares, birds, insects, and fruits) were consumed from time to time. Martens showed a compensatory response between preying on small mammals and eating fruits in summer and autumn months, and also between preying upon small mammals and birds in winter and spring months. The diet of foxes was characterized by a small annual variation and a High seasonal variation in the study area as compared with areas supporting high vole densities.