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Insectivorous birds reduce arthropod abundances and their damage to plants insome, but not all, studies where predation by birds has been assessed. The variation in birdeffects may be due to characteristics such as plant productivity or quality, habitat complexity,and/or species diversity of predator and prey assemblages. Since agroforestry systems vary insuch characteristics, these systems provide a good starting point for understanding when andwhere we can expect predation by birds to be important. We analyze data from bird exclosurestudies in forests and agroforestry systems to ask whether birds consistently reduce theirarthropod prey base and whether bird predation differs between forests and agroforestrysystems. Further, we focus on agroforestry systems to ask whether the magnitude of birdpredation (1) differs between canopy trees and understory plants, (2) differs when migratorybirds are present or absent, and (3) correlates with bird abundance and diversity. We foundthat, across all studies, birds reduce all arthropods, herbivores, carnivores, and plant damage.We observed no difference in the magnitude of bird effects between agroforestry systems andforests despite simplified habitat structure and plant diversity in agroforests. Withinagroforestry systems, bird reduction of arthropods was greater in the canopy than the croplayer. Top-down effects of bird predation were especially strong during censuses whenmigratory birds were present in agroforestry systems. Importantly, the diversity of thepredator assemblage correlated with the magnitude of predator effects; where the diversity ofbirds, especially migratory birds, was greater, birds reduced arthropod densities to a greaterextent. We outline potential mechanisms for relationships between bird predator, insect prey,and habitat characteristics, and we suggest future studies using tropical agroforests as a modelsystem to further test these areas of ecological theory.