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Beak length, gizzard width and intestinal length were all similarly related to body mass in gleaning, insectivorous, passerine birds from Malaysia, New Guinea and Australia. The remaining morphological difference between the three groups were attributable more to functional constraints than to phylogenetic affinities. The more tropical birds had slightly longer, but not proportionately narrower, beaks and smaller gizzards than comparable Australian birds. It is suggested that this stems from tropical species taking more soft-bodied and/or mobile prey than birds from the more arid Australian region.