Operant conditioning and multidimensional scaling (MDS) procedures were used to study auditory perception of complex vocal signals in budgerigars. Response latencies were anlyzed by MDS to produce a spatial arrangement of these complex sounds reflecting the perceptual organization. Both normal and isolate-reared budgerigars and humans show perceptual categories which correspond closely to the major functional and acoustic categories of species-specific calls. Birds sharing the same learned call show perceptual categories for the calls of individual birds. Humans and other budgerigars unfamiliar with these same learned calls fail to group calls by individual. These results suggest that both general and special auditory mechanisms are involved in the formation of perceptual categories for species-specific vocal signals in budgerigars. Additional tests with human speech sounds suggest that the general auditory processing mechanism in budgerigars are quite sophisticated. [Work supported by NIH.]