Population declines of many avian species are often attributed to increased rates of nest predation in fragmented landscapes, yet mechanisms underlying these effects have rarely been examined. We reviewed the literature to determine the extent to which hypotheses about nest predators and fragmentation have been invoked and compared this to the number of direct tests of predators with respect to habitat edge, patch size, or landscape type. We also conducted a meta‐analysis of tested predator effects to evaluate whether predator responses—numerical, functional, or species richness—to fragmentation depend on spatial scale (edge, patch, or landscape), landscape type, geographic region, or predator taxa. We found 120 papers containing hypotheses about nest predators and fragmentation, but only 31 with hypothesis tests. Most tests were of a single predator species or guild, whereas most cited hypotheses generalized across broader taxonomic groups. Results of predator tests were variable, but some general patterns were evident. Predator effects, including increased abundance, activity, or species richness in edges, small patches, or certain landscapes, were more prevalent (1) in tests conducted at the landscape scale than at the local scale, ( 2) in agricultural landscapes than in predominantly forested landscapes, (3) in certain biogeographic regions, and (4) for avian predators than for mammalian predators. Local‐scale (edge and patch) effects were most common when the land surrounding patches was agricultural and when tests were conducted within agricultural landscapes. The response of nest predators to fragmentation is complex, taxon‐specific, and context‐dependent. Conservation efforts for declining avian species may therefore need to be customized according to the nest‐predator species primarily responsible for local nest mortality and the nature of the landscape mosaic.

Many studies have compared songbird nesting success between forest edge and interior, but few have addressed potential factors underlying variation in nest predation pressure in relation to edge. We examined the relative abundance and species richness of songbird nest predators and the abundance of Brown-headed Cowbirds (Molothrus ater) in forest edge and interior within a fragmented, agricultural landscape in central Missouri, USA. Avian predators and cowbirds were more abundant in forest edges. There were no differences in small-or medium-sized mammalian predator abundance between edge and interior. Almost twice as many snakes were captured in edge as in interior. Predator species richness was significantly higher in forest edge. Forest vegetation structure was very similar between edge and interior, suggesting that differences in predator abundance and species richness were not driven by variation in habitat structure. Nest predator distribution in relation to habitat edge may therefore depend on factors at larger spatial scales, such as landscape context. We suggest that in areas fragmented by agriculture, nest predator assemblages in forest edges may differ from those in forest interior. Edges may attract a greater number of predator species, and some nest predators may be more abundant near the edges of forest patches, although the trend does not apply across all predator taxa. Generalizations about nest predators and edges should thus be made with caution, and conservation plans should consider the composition of local nest predator assemblages in order to predict potential impacts on nesting birds in edge habitat.

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