Sap feeding by the marsupial Petaurus australis: an enigmatic behaviour?

The Yellow-bellied Glider, Petaurus australis, was observed to feed sporadically but extensively on eucalypt sap. Gliders extracted sap by making incisions into the bark with their procumbent lower incisor teeth and licking the resulting exudate. Less than 1% of possible trees were incised for sap. Sap flow and sap-sugar concentration were estimated for eight sap-site trees and eight non sap-site trees at intervals during an 18 month period. Measurements of sap-sugar concentration differed substantially among trees but fluctuated between sample periods independent of glider use. Sap flow measurements, were always higher for those trees currently 'in use' by gliders, although the particular sap-site trees comprising this group varied between sample periods. The variation in sap flow occurred indenpendent of the incidence of rainfall or the type of microhabitat the tree occupied. Experimental incising of trees, designed to mimic the effects of feeding by gliders, failed to show any effect on sap flow. This suggests that the incidence of sap feeding is determined by a tree's pattern of sap flow and that there may be trees with unusual patterns of sap flow which gliders select as the most favourable trees to incise.