Lack of relationship between forest edge proximity and nest predator activity in an eastern Canadian boreal forest

Nest predation risk often increases near forest edges in agricultural landscapes, but this pattern has rarely been found in forested landscapes. Whether this lack of relationship is general remains unclear, especially because no assessment of statistical power has been published. To (1) assess whether and how far nest predation risk is associated with forest edges and (2) avoid confounding effects of the surrounding landscape, we measured nest predator activity by placing baits at five distances (0, 30, 60, 90, and 120 m) from sharp, rectilinear forest edges that run along extensive tracts of forest. No association was found between distance to forest edges and bait discovery rates (P = 0.7). The lack of edge effect was unlikely to be caused by a lack of statistical power (1 b > 0.8). However, bait discovery rates were significantly heterogeneous throughout the study area, and ground baits were taken at a greater rate than arboreal baits. Mice, voles, and red squirrels (Tamiasciurus hudsonicus (Erxleben)), all nest predators, were the main users of bait. Red squirrel occurrence, as estimated by playbacks, was higher in black spruce (Picea mariana (Mill.) BSP) than in balsam fir (Abies balsamea (L.) Mill.) stands but was not associated with a high bait predation rate. Our results strengthen support to the hypothesis that nests near open areas in managed boreal forests are not more at risk than forest-interior nests.