The diet of urban foxes (Vulpes vulpes) and the availability of anthropogenic food in the city of Zurich, Switzerland

Abstract

The diet of urban foxes and the availability of anthropogenic food were studied in the city of Zurich, Switzerland. A stomach analysis of 402 foxes, which were shot or found dead between January 1996 and March 1998, showed a broad variety in the diet of urban foxes, with a dominance of scavenged meat, other scavenge and cultivated fruit and crops. More than half of an average stomach content was anthropogenic. The proportion of anthropogenic food was increased in stomachs from the city centre - mainly due to the increasing proportion of scavenged meat - compared with stomachs from the periurban area. Significant seasonal variations in the diet were found for invertebrates, birds and for cultivated fruit and crops, which were all most frequently consumed in summer. A written survey among the inhabitants of three municipal districts showed that 85% of the households provided anthropogenic food which was accessible to foxes. This food supply consisted of three quarters of rubbish and compost, completed by fruit and berries and, to a lesser extent, food provisions for pets, birds, and other wild animals. In contrast, the anthropogenic food supply of allotment gardens mainly consisted of berries, completed by fruit, compost and birdseed. The anthropogenic food supply in public areas was determined by transects. The overall food supply of households, allotment gardens and public areas would be sufficient to feed a much higher number of foxes than currently present. This overabundance of food resources could explain the continual increase of urban population densities. A possible further exploitation of anthropogenic food sources is discussed considering its specific characteristics and the necessary behavioural adaptations.