Some species of birds form large flocks that forage on agricultural fields and frequently damage the crop, resulting in significant economic losses. Additionally, by defecating they potentially contaminate the crop and farm equipment with pathogens, which is of special concern for leafy greens that are consumed uncooked. There is a need to find an effective deterrent that is also environmentally friendly, and falconry is an ideal candidate for this purpose. To evaluate falconry as deterrent of nuisance birds in leafy greens field in northern California, we performed a set of trials on a control ranch and a treatment ranch of similar production and landscape characteristics. We identified avian species, counted individuals, and recorded flock size in daily surveys pre-treatment, during treatment (falconry), and post-treatment. Bird abundance was lower in spring than in fall, probably because many fields were fallow in spring. In both seasons, we observed a large daily variation in the bird abundance and their use of the fields in the surveys pre-treatment. In fall, the first trial was interfered by the activity of a falconer in an adjacent vineyard and the harvest of the grapes. Importantly, in the second trial, use of the field (e.g., foraging, etc.) decreased during five days of treatment and continued to be low for three days post-treatment, suggesting a “memory effect” after hazing by falconry. Interestingly, the third fall trial coincided with the end of the leafy greens growing season and showed that falconry successfully minimized use of the field by nuisance birds during peak activity. These results indicate that falconry is an effective measure to protect leafy green crops from fecal contamination and damage, but further research is needed at more farms in different regions, and the effect of using falconry in combination with other non-lethal bird abatement approaches (e.g., audio-visual deterrents) should also be evaluated.