Review The Effect of Edge on Avian Nest Success: How Strong Is the Evidence?

Abstract: Wildlife biologists historically considered the edge between adjacent habitat ypes highly productive and bene-ficial to wildlife A currant dogma is that edges adversely affect a wide range of avian species by increasing depreda-tion and parasitism rates of nest ~ I critically evaluated ex-isting empirical evidence to test whether there was a grada-tion in nest success as a function of distance from an edge Researchers investigating this question have been inconsis-tent in their experimental design ~ making generalizations about edge-effect patterns difficul £ The majority o f studies I examined found nest success varied near edge ~ with both depredation rates (10 of 14 artificial nest studie ~ and 4 of 7 natural nest studies) and parastttsm rotes (3 of 5 studies) increasing near edger In addittor ~ there was a positive rela. tlonship between est success and patch size (8 of 8 studies). The most conclusive studies uggest that edge effects usually occur within 50 m of an edgg whereas tudiesproposing that increased epredation rates extend farther than 50 m from an edge are less convincing. Prior research as probably fo-cused on distances too far from an edge to detect hreshold value ~ and future research should emphasize smaller scale~. 100-200 m from an edge at 20-25 m inotnnent ~ Research-ers often use relatively arbitrary habitat characteristics to define an edge Therefore, Ipropose that only openings in the forest cxmopy with a diameter three times or more the height of the adjacent rees should be included in edge analyse,~ This review suggests that fragmentation of eastern North Ame~can temperate forests could lead to increased nest pre-dation and parasitisnt and there is need to determine i f similar processes occur in other forested regions of Nort