Food preferences of Knysna and purple-crested turacos fed varying concentrations of equicaloric and equimolar artificial fruit.

The effects that different fruit sugar types and concentrations have on food preferences of avian frugivores have been relatively poorly studied. Although it has been recently advocated that preference is based on equicaloric energy it is also important to note whether preferences change as energy content changes. Therefore, sugar preferences of equicaloric and equimolar artificial fruit of different sugar types at varying concentrations and molarities were investigated in two relatively large South African frugivores, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos. Artificial fruits containing 6.6, 12.4 or 22% sucrose or glucose, and artificial fruits containing 0.42, 0.83 or 1.66 mol l(-1) sucrose or glucose, were used to determine sugar preferences. Knysna turacos preferred the sucrose to the glucose equicaloric artificial fruit diet at low concentrations whereas purple-crested turacos showed no preference for either diet. Both turacos species preferred the sucrose equimolar artificial fruit diet to the glucose at low concentrations. At high concentrations neither species showed a preference for either equicaloric or equimolar artificial fruit diets. This suggests that energy requirements influence food preferences more than sugar type and that birds will select fruit that is higher in energy irrespective of sugar type. This complements an earlier study on digestion of differing equicaloric and equimolar artificial fruit sugar types. It again emphasizes the need for future studies looking at the composition of indigenous forest fruit sugars in order to obtain insight into the role of these avian frugivores as potential seed dispersers of fruiting tree species.