Dietary diversification of an insect predator along an urban-rural gradient

• Urban bats exhibit higher trophic diversity than rural conspecifics. • Urban bats consume more agricultural pests and also nuisance insects. • Environmental factors correlate with the diversity of the insect diet of bats. • Bats mitigate disease transmissions and enhancing public health by feeding on nuisance insects. Urbanisation generally leads to a loss of taxonomic and functional diversity in almost all animal taxa, yet a mosaic of highly variable habitats within the urban matrix could offer a diversity of insect prey to highly mobile predators such as bats. We therefore asked if insect-feeding bats change in trophic interactions along rural–urban gradients. We predicted that the diet of common noctule bats ( Nyctalus noctula ) diversifies with increasing levels of urbanisation and that urban bats include more pest and nuisance insect species than rural conspecifics. Using metabarcoding of faecal samples over three years of sampling, we observed a more diverse diet in urban compared with rural noctule bats. Furthermore, urban bats consumed more than twice as many agricultural pests and six times as many nuisance insects as their rural conspecifics. Finally, insect species richness in the diet decreased with increasing levels of sealed surface and vegetation cover at the sampling site. We argue that a highly mobile bat species such as the noctule bat compensate for the lower abundance of insects in urban areas by foraging over relatively large spatial scales, including adjacent rural areas. A high proportion of pest and nuisance insects highlights the importance of urban bats for providing important ecosystem services to humans. Urban planning needs to consider maintaining and establishing dark flight corridors and a diversity of habitats to support urban bat populations.