Repellency of Sucrose to Captive American Robins

American robins (Turdus migratorius) are often pests of commercial fruit crops in North America. Because robins lack sucrase and cannot digest sucrose, they may develop an aversion to high-sucrose fruits. Thus, I tested captive robins with aqueous solutions of 15% (g/mL) mixed sugars (x% sucrose + y% glucose and fructose mixture = 15% sugar) to identify the level of sucrose required to develop a conditioned feeding aversion when digestible sugars are present. In 1-tube tests, robins decreased intake of 15% sucrose solutions 50% below baseline, but maintained stable intake of 3.75% and 7.5% sucrose solutions. In 2-tube tests with sucrose solutions paired against a glucose-fructose solution, robins avoided the 15% treatment in the first hour of testing (P < 0.05), yet were indifferent in the full 4-hour test (P > 0.05). My data suggest that a fruit cultivar would require as much as 15% sucrose to repel robins, and such high sugar concentrations naturally occur in fruits. Development of high sucrose cultivars would require almost complete replacement of simple sugars by sucrose and might be possible through selective breeding.