Fig. 1. Scoring of beak and dance movements. Eight successive frames (taken at 33 ms intervals) from a video tape of adult male zebra finch Y125 directing his song to a female (not visible, but present immediately beyond the left edge of the frame) are shown. The change in beak angle from the preceding frame and the overall net percentage of change in beak aperture for the associated song segment are given for each frame. The sequence includes one ‘dance’ movement, a shift in head and body angle between frames 3 and 4 (note that this shift also changes the perspective of the beak). Several changes in beak aperture are also apparent, most notably between frames 3 and 4 and frames 7 and 8. See the text for further explanation of the scoring of these dance and beak movements.