Techniques for evaluating the efficacy of chemical repellents applied to crops against depredating birds are presented. Curb (aluminum ammonium sulfate) has shown promise as a repellent against several species of granivorous birds when applied to ripening cereals in West Africa. In all the trials, one treatment of 8 to 16 kg/ha protected the ripening grain of rice, millet, and sorghum for between one and two weeks, and, under particular conditions, two treatments gave protection throughout the maturational period.