ON THE SELECTION OF TREE SPECIES BY ACANTHIZIDAE IN OPEN-FOREST NEAR SYDNEY, NEW-SOUTH-WALES

Selection between tree species as foraging substrates by four species of Acanthizidae was studied in an open eucalypt forest near Sydney, Ne w South Wales. Weebills Smicrornis brevirostris, Striated and Little T hornbills Acanthiza lineata and A. nana foraged more often than expect ed on the foliage of Narrow-leaved Ironbark Eucalyptus crebra than on that of Grey Box E. moluccana. By contrast Gerygone olivacea used the two trees in about the same proportion as the amount of foliage of eac h species. Weebills and Striated Thornbills selected Narrow-leaved Iro nbark foliage as a foraging substrate more often than Little Thornbill s in winter but not in spring. Little Thornbills foraged on Narrow-lea ved Ironbark foliage more often in spring than in winter. The selectio n of eucalypt foliage as a foraging substrate is correlated with the a bundances and kinds of invertebrates found on the two tree species. In vertebrates were generally more abundant on the foliage of Narrow-leav ed Iron-bark than on that of Grey Box in both winter and spring. Lerp- forming psyllid insects, however, were more abundant per leaf on Grey Box than Narrow-leaved Ironbark in winter, but not in spring, Grey Box leaves are larger than those of Narrow-leaved Ironbark and when the a bundances of psyllids were corrected for leaf area (i.e. as numbers/cm (2)), the difference between Grey Box and Narrow-leaved Ironbark in wi nter was not significant. However, in spring the numbers of psyllids/c m(2) on Narrow-leaved Ironbark foliage was greater than on Grey Box fo liage. The differences in invertebrate abundances account for some of the differences in the use of the two eucalypts as foraging substrates , but variability in invertebrate abundances between leaves and indivi dual trees, as well as differences in foliage morphology, may also hav e been important.