Digestive efficiency of Knysna and purple-crested turacos fed varying concentrations of equicaloric and equimolar artificial fruit

Avian frugivores have been somewhat poorly studied with regards to the effects that different fruit sugar types and concentrations have on their digestive efficiencies. Therefore, two relatively large South African frugivores, the Knysna turaco (Tauraco corythaix) and the purple-crested turaco (Gallirex porphyreolophus), were fed artificial fruit that contained equicaloric and equimolar concentrations of different sugars, to determine their daily food and energy intake, digestive efficiencies and digestive transit times. The artificial fruit contained 6.6, 12.4 or 22%, or 0.42, 0.83 or 1.66 mol l(-1) sucrose or glucose. Food intake of both turaco species increased with decreasing sugar concentration and molarity, irrespective of sugar type, suggesting compensatory mechanisms for energy requirements. Apparent assimilation efficiencies of both turaco species ranged from 61.4-90.0% and 60.2-92.4% for equicaloric and equimolar artificial fruit diets, respectively. Digestive transit times for both turaco species were slowed with an increase in sugar concentration and molarity, irrespective of sugar type. Consequently these two frugivores appear to be tolerant of sugar type and would be expected to select fruits based on energy yields. Future studies of the composition of indigenous forest fruit sugars may give insight into food preferences of the turaco species and their role as potential seed dispersers of fruiting tree species.