Cost-distance analysis of mesopredators as a tool for avian habitat restoration on a naturally fragmented landscape

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Journal of Wildlife Management





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Removal of mammalian mesopredators is a strategy frequently applied to problems of conservation management, such as protection of rare or endangered species. Effectiveness of predator removal is often dependent on the ease with which additional predators can immigrate into the removal area. We applied cost-distance analysis, coupled to a sensitivity analysis, and least-cost path analysis to raccoons (Procyon lotor) and red foxes (Vulpes vulpes) on the Virginia barrier islands to determine the landscape resistance (i.e., difficulty) for mesopredators to reach individual islands from both mainland and island sources, to assess the relative role of mainland versus island populations as sources of immigrants to unoccupied (or depopulated) islands, and to formulate strategies that focus management efforts on a few key predator sources. The minimum energetic resistances to immigration varied over 3 orders of magnitude, making some islands better targets for removal efforts than others. Additionally, because of differences in the distribution of resident populations on the islands, resistance to immigration to a typical island is at least 3 times less for raccoons than for red foxes. Landscape resistance to red fox immigration is typically lower from the mainland, whereas for raccoons inter-island movements are typically less costly. Empirical data from long-term field studies of raccoons and red foxes in this system support the resistance structure identified. Overwater transits made by marked and resighted raccoons all were relatively short and relatively low-cost. Similarly, islands that were recolonized following the removal of raccoons and red foxes all were characterized by very low resistance values. These results are used to identify specific islands for which predator removal efforts are most likely to be successful in aiding the recovery of beach-nesting and colonial waterbirds in this system. A similar approach may be applied in any landscape where there are distinct differences in the costs of traversing different elements of the landscape.