Perception of song syllables taken from natural song sparrow and swamp sparrow songs was examined in five different species: song sparrows (Melospiza melodia), swamp sparrows (Melospiza georgiana), zebra finches {Taeniopygia guttata catanotis), canaries iSerinus canaria), and budgerigars (Melopsittacus undulatus). Using operant conditioning techniques, we trained these birds to discriminate among sparrow song syllables. By testing the birds on all possible pair-wise combinations of syllables, we generated "similarity" matrices for these song syllables from the birds'response latencies to detect changes in a repeating background of syllables. A number of different statistical techniques were used to examine species differences in perception including factor analysis of an inter-species correlation matrix, cluster analysis ofthe similarity matrices, and individual-differences multidimensional scaling (MDS) of the similarity matrices from each species. The spatial map of these stimuli produced by MDS revealed the perceived relations among these syllables for each species. Several acoustic measurements taken from these syllables were correlated with stimulus coordinates of the syllables in multidimensional space. These results demonstrate that natural vocal signals can be effectively used as stimuli in psychoacoustic experiments and the outcome of such experiments are likely to reveal robust species differences in perception.