Maize-field complexity and farming system influence insectivorous birds’ contribution to arthropod herbivore regulation
The contribution of insectivorous birds to reducing crop damage through suppression of herbivory remains underappreciated, despite their role as cropland arthropod predators. We examined the roles of farming system, crop cover pattern, and structural configuration in influencing assemblage composition of insectivorous birds and their herbivorous arthropod prey across maize fields, and determined how bird exclusion affects crop herbivory levels. To achieve these objectives, we collected data across a sample of organic and conventional small-scale non-Bt maize farms in western Kenya. Assessments of abundance, diversity, and richness of insectivorous birds and abundance of their arthropod prey were compared between organic and conventional small-scale non-Bt maize on monocultured and inter-cropped farms. We also employed bird exclusion experiments to assess impacts of bird predation on herbivorous arthropod abundance. Results showed that higher structural heterogeneity supported higher insectivorous bird richness, particularly under organic systems, dense trees, large woodlots, and thick hedgerows. Bird abundance further increased with crop diversity but not in relation to cropping method, hedgerow type, or percent maize cover per se. Conversely, herbivorous arthropod abundance and richness increased on conventional farms and those with higher percent maize cover, but were unaffected by cropping methods, tree, or hedgerow characteristics. Birds' arthropod prey was more abundant under completely closed experimental plots compared with open or semi-closed plots, confirming a significant linkage between birds and herbivorous arthropod suppression. In this study, we demonstrate importance of structural heterogeneity in agricultural landscapes, including diverse croplands and on-farm trees to maximize insectivorous birds' contribution to reducing crop arthropod herbivory.
Author(s): Otieno, NE; Jacobs, SM; Pryke, JS