Summary
Cats and ferrets were less abundant within the fenced part of the wetland (39 ha) than the adjacent, unfenced part (40 ha). Mice and Norway rats were more abundant within the fenced than the unfenced part of the wetland. For five bird species, we measured some or all of hatching success, fledging success, and productivity (chicks fledged per female per season), and found no clear differences between the fenced and unfenced sites.
Our results do not support further use of this particular design of predator-fence. The fence plus trapping regime did not effectively exclude predators from the wetland, did not deliver benefits to nesting birds, and was expensive. A better use of resources would have been to either build a fully predator-proof fence at Ruataniwha wetland, or no fence at all and invest the resources elsewhere. We briefly review previous attempts at predator exclusion using fences and conclude that they should be built only when the design has been proven, and there is strong evidence that the conservation benefits will justify their initial and ongoing costs.
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