Long-term changes in the feeding pattern of red foxes Vulpes vulpes and their predation on brown hares Lepus europaeus in western Poland

The aim of this study was to estimate long-term changes in the winter feeding pattern of red foxes Vulpes vulpes and in their predation on brown hares Lepus europaeus in relation to the decreasing abundance of hares in western Poland in 1965/1966-2006/2007. The frequencies of occurrence in the stomachs of culled foxes (N = 726) were used as indices of prey capture rates. The average autumn density of brown hares in the study area decreased from 48 individuals/km(2) at the turn of the 1960s and 1970s to seven individuals/km(2) in 1999-2006. Hares and small rodents were the main food classes of foxes in western Poland at the turn of the 1960s and 1970s; however, the occurrence of hares in the fox diet subsequently decreased, and they were replaced by livestock carrion. The relationship between the occurrence frequency of hares in the fox diet and the hare density was best described by sigmoid equation. It indicates that the red fox showed a type III functional response to long-term changes in hare abundance. When predation rate index was estimated on the basis of functional response, the potential fox predation was density-dependent at low to intermediate hare densities (< 25 individuals/km(2)). This finding suggests that the increase in the number of low-density hare populations may require intensive management measures, e.g. simultaneous use of fox control and habitat improvement.