Sucrose repellency to European starlings: will high-sucrose cultivars deter bird damage to fruit

European Starlings (Sturnus vulgaris) are often pests in commercial fruit crops in North America and Europe. Because starlings slack the digestive enzyme sucrase and cannot digest sucrose, they may develop an aversion to high-sucrose fruits. In water-tube drinking trials, we tested captive starlings with aqueous solutions of 15% (mass/volume) mixed sugars to identify the level of sucrose required to develop a conditioned feeding aversion when digestible sugars are present. In one-tube tests, starlings decreased intake of 11.25 and 15% sucrose solutions relative to their pretest intake of a 15% glucose-fructose mixture. In two-tube tests with sucrose solutions paired against a digestible glucose-fructose solution, starlings decreased preferences for the sucrose solutions as sucrose concentrations increased. These data suggest that the presence of digestible nutrients mitigates the effect of sucrose in sucrase-deficient birds and that a fruit cultivar would require @> 11.25% sucrose to repel starlings.