Fig. 2. Effects of ethanol concentration on the marginal value of food containing fructose, sucrose or glucose for female (left panels) and male (right panels) Egyptian fruit bats. Marginal values were estimated using giving-up density (GUD). The difference between the GUD of the sugar-containing foods tested was significantly greater when the foods contained 1% ethanol than when they were ethanol free (one and two asterisks indicate significance at the P<0.05 and P<0.01 level, respectively). By increasing ethanol concentration in the food, the marginal value of food+fructose decreased relative to food+sucrose (A,B) and increased relative to food+glucose (C,D). The marginal value of food+sucrose increased relative to that of food+glucose with ethanol abundance (E,F). Error bars are 1 s.d.