Sugar preferences and digestion by Cape white-eyes, Zosterops virens, fed artificial fruit diets
Sugar preferences and digestion of sugars in artificial fruit of different sugar types and concentrations were investigated in a South African facultative frugivore, the Cape white-eye (Zosterops virens). We studied sugar preferences, daily food and energy intake, and digestive efficiencies and transit times with birds that were fed artificial fruit diets comprising 6.6, 12.4 and 22% glucose and sucrose, respectively. Digestive transit rates of birds fed artificial fruit diets were faster for glucose compared with sucrose diets, irrespective of concentration. Birds showed increased food intake with decreasing glucose concentration, but showed no significant differences in these intake amounts with differing sucrose concentrations. Apparent assimilation efficiencies were lower than most nectar studies, and were generally higher for glucose fruit (79.3–85.6%) compared with sucrose fruit (69.0–78.4%). In choice tests, birds preferred sucrose over glucose of equivalent weight, irrespective of concentration. It appears likely that the Cape white-eye has high levels of sucrase activity, although further study is needed to verify this.
Key words: frugivory, sugar, fruit composition, digestion, preference, Cape white-eye, Zosterops virens.