First published online December 14, 2007
Journal of Experimental Biology 211, 66-78 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.011908
Singing with reduced air sac volume causes uniform decrease in airflow and sound amplitude in the zebra finch
Emily Megan Plummer and
Franz Goller*
Department of Biology, University of Utah, Salt Lake City, UT 84112,
USA
View larger version (35K):
[in this window]
[in a new window]
|
Fig. 1. Example of zebra finch song illustrating physiological and acoustic data.
Terminology used for description of different temporal units of song is
explained using the air sac pressure trace (P): i, introductory notes. Inset
shows the three different syllables corresponding to expiratory pulses of the
song motif (1, 2 and 3), interrupted by minibreaths (a and b). Air sac
pressure patterns differ markedly between quiet respiration and song.
Expiratory pressure is defined as pressure values above and inspiratory
pressure as values below the ambient pressure line (orange horizontal line),
respectively. Tracheal airflow (F) shows a regular flow pattern during quiet
respiration and the altered temporal and amplitude pattern during song. The
flow data do not indicate direction of airflow, but the direction can be
inferred from air sac pressure. The sound is shown spectrographically (bottom
panel).
|
|
View larger version (32K):
[in this window]
[in a new window]
|
Fig. 2. A schematic of the avian respiratory system, illustrating the major air
sacs and their connections to the lung. (A) The lateral and dorsal direction
of motion of the rib cage during exhalation is indicated by arrows. (B) The
direction of airflow during inspiration. (C) The direction of flow during
expiration.
|
|
View larger version (29K):
[in this window]
[in a new window]
|
Fig. 3. One bird displayed distinct periods of apnea after song bouts. These
periods shortened after the first injection and were shortened or no longer
present after the second injection. (A) Air sac pressure traces of song bout
before injection (blue) and after two injections (green). (B) Apnea duration
before injections (blue circles) was positively correlated with bout duration
(linear regression, r=0.65, P=0.0059), but injections
reduced or eliminated periods of apnea (red, one injection; green, two
injections).
|
|
View larger version (22K):
[in this window]
[in a new window]
|
Fig. 4. (A) Mean percent (±1 s.e.m.) of pre-injection air sac pressure
(top), and reduction in sound amplitude (bottom) for the one, two, missed and
missed-plus-one-injection groups. Different letters indicate significant
differences in t-tests (where different birds) and paired
t-tests (same bird different treatments). For all significant
comparisons, P<0.028. (B) The variation of air sac pressure
amplitude was not increased after injection into one (red) or two (green)
posterior thoracic air sacs compared with that of pre-injection values (blue).
Each trace represents the mean air sac pressure ± 1 s.e.m. (grey area
around mean) for 10 renditions of the song syllable in each treatment.
Increased grey area at the beginning and end of traces results from slight
differences in duration of the expiratory air sac pressure pulse between
renditions of the song, which leads to imperfect alignment.
|
|
View larger version (50K):
[in this window]
[in a new window]
|
Fig. 5. Air sac pressure (P), tracheal airflow (F) and sound amplitude (A) during
song were increasingly reduced after one (red) and two (green) injections into
the posterior thoracic air sacs, as compared with pre-injection (blue). A
representative song is also shown spectrographically before and after two
injections. During the first and second expiratory pulse, the bird closed its
syrinx (as indicated by zero tracheal flow; arrows), resulting in elimination
of these sound segments. Quiet respiration changed after injections into the
posterior thoracic air sacs. The orange horizontal line depicts ambient
pressure.
|
|
View larger version (18K):
[in this window]
[in a new window]
|
Fig. 6. In zebra finch Y34, air sac pressure was reduced uniformly throughout
expiratory pulses, but airflow reduction increased at the end of pulses. The
top panel shows the air sac pressure traces for the two syllables (P) of the
motif for pre-injection (blue), one injection (red) and two injections
(green), with the percent reduction from pre-injection for each injection
trace indicating a fairly uniform reduction. Cumulative airflow for each
syllable (bottom panel; shown as cumulative flow) indicates not only the
overall decrease in flow after injections but also that, at the end of
syllables, increases in airflow present in pre-injection song cannot be
sustained by the injected bird (change in slope marked by arrows).
|
|
View larger version (40K):
[in this window]
[in a new window]
|
Fig. 7. Zebra finch W42 showed a consistently increasing difference in air sac
pressure (shown in direct comparison, P, and below as percent decrease from
pre-injection values; colors as in Fig.
5) amplitude throughout each expiratory pulse. Song output during
all three treatments is shown as amplitude traces (A; rectified and
integrated) and as spectrograms (pre-injection and two injections) and
illustrates how particularly high-frequency syllables are reduced in amplitude
after the injections. Each of the two sets of high-frequency syllables is a
combination of one element produced at the end of an expiratory pulse and the
second during the following inspiration (phonatory minibreath). In both sets,
the expiratory element disappeared (almost zero amplitude) whereas the
inspiratory part was strongly reduced in amplitude.
|
|
View larger version (42K):
[in this window]
[in a new window]
|
Fig. 8. Zebra finch B4 showed a decrease in duration of two syllables and yet
retained air sac pressure and airflow throughout. In A, the change in duration
of the long expiratory pulse (612 ms) is evident by the comparison between
pre-injection pressure (blue) and pressure after two injections (green). B
shows the decreased pressure in each syllable in areas where the pressure
pulses remain similar in spite of the duration change. The descent of the
difference in the second syllable is due to change in duration. C shows the
cumulative flow of each syllable, which shows the overall decrease in airflow
from pre-injection (blue) to one injection (red) and two injections (green).
Sound is shown as rectified and integrated amplitude (D) and
spectrographically (E). The change from smooth frequency modulation
(pre-injection) to a complex harmonic structure (two injections) can be seen
in the long syllable in the spectrograms.
|
|
View larger version (8K):
[in this window]
[in a new window]
|
Fig. 9. Birds sang with shorter bout duration after injections. Cumulative
frequency plots of relative bout durations expressed as a percentage of the
longest pre-injection bout (using 10% bins) are shown for the three treatments
(blue, pre-injection, N=99; red, one injection, N=80; green,
two injections, N=101) for all birds.
|
|
View larger version (38K):
[in this window]
[in a new window]
|
Fig. 10. Air sac pressure (P) and sound amplitude (A) during song were increasingly
reduced after two injections (green) into the posterior thoracic air sacs of
one bird, V74, as compared with pre-injection (blue). The reduction or total
loss of high frequency notes is shown in the sound amplitude trace (A) and in
the spectrogram (bottom).
|
|
View larger version (37K):
[in this window]
[in a new window]
|
Fig. 11. Electromyogram (EMG) activity does not indicate a compensatory increase in
muscle activity after injections. (A) Example of data for one zebra finch
illustrates the decrease in air sac pressure (P) after two injections (green)
compared with pre-injection (blue) to two injections and the accompanying EMG
activity (E; rectified and integrated). The song is illustrated
spectrographically (bottom). (B–D) Air sac pressure and corresponding
EMG activity (integrated voltage) for the three zebra finches for quiet
respiration and song. Colors indicate the three recording conditions (blue,
pre-injection; red, one injection; green, two injections). The data in B are
from the individual whose song is depicted in A, and numbers correspond to the
four expiratory pulses of song. Arrows indicate the shift in air sac pressure
after injections for the four expiratory pulses of song. C shows that the
first injection was followed by an increase in EMG activity, which is most
pronounced in the syllable in the upper right corner. However, a corresponding
shift in EMG activity is seen in quiet respiration, at the bottom left of the
graph, likely indicating an impedance change.
|
|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
© The Company of Biologists Ltd 2008
