Potential effects of reserve size on incidental nest predation by red foxes Vulpes vulpes

Red foxes Vulpes vulpes were observed foraging in sites occupied by nesting waders and waterfowl in the Lower Derwent Valley in northern England. The data obtained were used to parameterise an individual-based simulation model of fox search behaviour, which was used to explore the sensitivity of nest encounter rates to changes of search area between 1 and 10 ha. The model predicted that nests in larger patches will have a much greater chance of surviving predation than nests in smaller patches for realistic foraging effort, assuming that the search time is equal in all patches. This qualitative result remained the same for a range of realistic nest detection efficiencies and movement parameters. Patch size was also shown to be important when the assumption of equal search effort between patches was relaxed. When foxes were assumed to search systematically in a zigzag path along strip habitats, nest predation risk was shown to be sensitive to changes in habitat width of a few metres, provided the habitats were long enough (more than ∼8 km). The implications for predation management and new research on fox behaviour are discussed.