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Choreography of song, dance and beak movements in the zebra finch (Taeniopygia guttata)

Heather Williams^*

Biology Department, Williams College, Williamstown, MA 01267, USA

View larger version (79K): [in a new window]   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.

View larger version (52K): [in a new window]   Fig. 2. Changes in beak aperture. The sonograms show the songs of (A) LB92, a 9-year-old male, and (B) LB60, a 3-year-old male. Beneath each song is a graph showing the proportion of songs that had beak-opening (positive-going columns) and beak-closing (negative-going columns) movements during the corresponding song segment in the sonogram of the male’s song. Where the values represented by the columns do not add to 100 %, the remaining songs showed no change in beak aperture during the song segment in question. The shading of the columns denotes whether the distribution of beak movements (opening, closing, no change) was different from the overall average for the song: white columns, no difference from the song average; light gray columns, beak movements differed significantly from the song average at the P<0.05 level; dark gray columns, significant at the P<0.001 level (2 analysis, d.f.=2). The filled circles mark the net change in beak position (the percentage of songs associated with beak-opening movements minus the percentage of songs associated with beak-closing movements) for each song segment; the curve showing the overall beak movement trajectory is a cubic spline fitted to the net change in beak position. The filled and open squares at the base of each sonogram denote syllable pairs (or separate segments of a single syllable) that were chosen, on the basis of the sonograms and the beak trajectories, for comparing similar sounds given with beak relatively open (open squares) or closed (filled squares). The letter designations above each sonogram denote different syllables as defined by the criterion that uses change in acoustic structure within a continuous sound to demarcate syllables. Syllables with the same letter but within different songs do not correspond in any way in this figure.

View larger version (75K): [in a new window]   Fig. 3. Comparisons of beak and dance movements for two father/son pairs. Each panel shows the songs of the father at the top and the son at the bottom. Boxes within the sonogram denote song elements present in the song of only one of the pair; these portions of the songs were omitted when matching frames from a father’s song to frames in the son’s song (the matching process was performed using the sonograms, without reference to data on movements). For this figure, the syllable designations in different songs within the same panel correspond to matching syllables (e.g., the syllables within W31’s song were considered to correspond to the syllables with the same letter designations within Bk58’s song). Syllables that had no match in the father’s or son’s song were designated with the letters Q, X, Y or Z. Syllables I, J and K in Pk61’s song were difficult to match unambiguously to corresponding syllables in his son’s song, and the correspondence involving the fewest rearrangements was chosen. The beak movement trajectories for the matching portions of the father/son song pairs are shown immediately beneath and in register with the father’s song. Filled circles connected by a solid line show the beak movements of the father, and open circles connected by a dashed line show the corresponding changes for the son (all lines are cubic splines fitted to the net beak movement, as in Fig. 2). The dance movements were registered and summarized in a similar fashion. Although the fits for the father’s and son’s beak movements and dance were not perfect, the major peaks correspond (see text for statistical analyses). The greatest divergences from a common pattern appear to fall in the segment of the Pk61/DP46 song that was difficult to match unambiguously (syllables I, J and K).

View larger version (38K): [in a new window]   Fig. 4. Acoustic correlates of opening and shutting the beak. (A) Differences in fundamental frequency for 14 syllable pairs (two syllables or portions of syllables from the same song with similar acoustic structure but differing in beak aperture, see Fig. 2 for examples). Error bars (± S.E.M.) for the fundamental frequency were generally so small as to be contained within the symbol, and fundamental frequency did not differ for the two beak positions. (B) Peak frequency (the frequency with the highest energy) was more variable, and showed a significant overall reduction when the beak was closed, although two syllables did increase in peak frequency. (C) The average relative amplitude also decreased significantly overall when the beak was closed (although three syllables increased in amplitude in this condition). (D) These trends are illustrated in two neighboring syllables from DP46’s song (also pictured as syllables Y and Z in Fig. 3B, but note that the beak trajectory for these syllables does not appear in that figure because the syllables were absent from the father’s song). Beak aperture was reduced during the first syllable and increased during the second syllable. The two syllables have nearly identical fundamental frequencies, but the second syllable, when the beak was relatively open, had a higher amplitude (as is apparent in the oscillogram and in the overall ‘darkness’ of the sonogram). The energy in the second syllable is concentrated in higher harmonics than for the first syllable; compare the fifth and sixth harmonics for the two syllables. Note that, because change in beak aperture and not the beak aperture itself was measured, the two beak positions (open and closed) are relative.

View larger version (49K): [in a new window]   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).