Fig. 2. Number of low-frequency chirps (mean ± s.e.m.) produced during playback stimulation as a function of Df in male (A) and female (B) A. leptorhynchus (open squares) and A. albifrons (closed circles). (A) Male A. leptorhynchus (N=11, open squares) produced more low-frequency chirps to stimuli close in frequency to their own EOD (within 20 Hz) than to distant frequencies (±150 Hz). Similarly, A. albifrons males (N=16, closed circles) produced more low-frequency chirps to stimuli 5 Hz lower than their own EOD compared to stimuli 150 Hz higher or lower. (B) There was no effect of Df on the production of low-frequency chirps in A. leptorhynchus females (N=9, open squares), although the trend was similar to the overall effect of Df seen in males. Female A. albifrons (N=15, closed circles) produced more low-frequency chirps to stimuli within 5 Hz of their own EOD than stimuli 150 Hz lower or higher. Data points with different letters differ significantly from each other; Tukey's HSD, P<0.05. NS, no significant effect of Df (repeated-measures ANOVA, P>0.05).