Pest management is a foremost challenge of California’s winegrape growers. Common methods to reduce rodent pests are expensive, labor intensive, and harmful to the environment. Barn owls (Tyto furcata) provide a promising alternative, though their effectiveness for pest control has received little ecological research. To help fill this gap, we deployed rodent chew blocks, trays mixed with seed and sand to measure giving up density (GUD), and remote cameras on three vineyards with and three without barn owl boxes in Napa Valley in February through July 2023. We found that the effect of owl nest boxes on rodent activity, as measured by chew blocks and camera traps, was mediated by vegetation cover. Likewise, the effect of expected barn owl hunting pressure on rodents’ perceived predation risk, as measured by GUD, also varied with vegetation cover. Specifically, vegetative cover dampened the effect of the presence of owl nest boxes, and rodents exhibited less response to owl hunting pressure in areas with high vegetative cover. These results help reveal where and when barn owls can meaningfully affect rodent pests in vineyards, and they also highlight how spatial and temporal variation in vegetation adds complexity to predator-prey dynamics for barn owls and their prey.