Fig. 5. Dance movements. The sonograms show the songs of (A) LB46 and (B) LB47, 3-year-old brothers that developed different songs. Beneath each sonogram is a bar graph showing the percentage of songs that included dance movements in the video frame corresponding to that song segment. The solid line is a cubic spline fitted to the data. The shading of the columns denotes frames that had dance movements that differed from the overall levels for the song (white columns, no difference from the song average; light gray columns, P<0.05; dark gray columns, P<0.001). As for the data shown in Fig. 2, the 
2 values were calculated on the basis of the actual numbers of movements scored and not on the percentages; thus, columns that appear to be similar may have different statistical significance because of differences in sample size (some zebra finches sing partial song strophes at the end of a song bout, so that the final syllables of the song are sung less often).
