Birds as suppliers of pest control in cider apple orchards: Avian biodiversity drivers and insectivory effect

Abstract

Making farming compatible with biodiversity conservation requires identifying the biodiversity drivers that operate in agricultural landscapes, while also addressing the role of biodiversity in ecosystem services. Such integrative information is, however, rare for specific biodiversity groups and services. Here, we focus on insectivorous birds in cider apple orchards in northern Spain, ascertaining the relationships between landscape- and orchard-scale features and bird biodiversity. We conducted field observations and experiments to estimate the potential of birds for controlling arthropod abundance and pest outbreaks in apple trees. Twenty-nine tree-dwelling, insectivorous bird species were observed during one year, inside and around cider apple orchards, with six abundant species representing a predictable core across sites and seasons. Bird abundance and richness increased with the availability of semi-natural woody habitats (hedgerows, remnant trees, and forest patches) both in the immediate neighborhood of the orchard and in the landscape within a 1-km radius of the orchard. Orchards with higher cover of apple tree canopy also harbored a greater abundance and richness of birds. Apple tree branches that were cage-excluded from birds and manually infested with aphids suffered increased shoot damage and aphid outbreak, compared to those that were aphid-infested but open to birds. Bird exclusion led to increased abundances of pest insects other than aphids, and also of other arthropods considered as natural enemies or mutualists of pests. Arthropod abundance was lower in those orchards showing higher abundances of insectivorous birds during spring and summer. Multi-scaled farming management, involving both within-field practices and regional land use schemes, should be considered in order to promote win–win scenarios in cider apple orchards, whereby species-rich assemblages of insectivorous birds provide effective pest control service.