Nest predation in forested regions: Landscape and edge effects

The generality of edge-related nest predation across different types of edges and in landscapes variously impacted by fragmentation has been debated in recent years. I investigated whether land uses within forested areas exerted stronger landscape-level than local-edge effects on avian nesting success. Ten study sites were selected within contiguous mature forest in central Pennsylvania, USA. Landscape composition (percent cover by different disturbances) was quantified within a 314-ha forested landscape surrounding each study site, and from this, I defined 2 forested landscape types (agricultural and silvicultural; n = 5 each) with similar ranges of forest cover within 1 km (45-82%). From May to July 1998 and 1999, 341 songbird nests were monitored to determine nesting success. For each nest, I measured the distance to it habitat edge (1-200+ m) and identified the type of edge (agriculture, timber harvest, unimproved forest road, or residence). At the local-edge scale, nest fate was not related to the distance from edge for the 4 common edge types. However, at the landscape scale, nesting success was tip to 2.6 times lower within forested landscapes disturbed by agriculture than within those disturbed by silviculture. Thus, Within forested landscapes, agriculture did not produce edge effects per se but did negatively impact forest birds at the landscape scale. These results provide evidence that, rather than edge effects being important within forested landscapes, the types of land uses within the landscape may in part determine predation rates.