Respiratory patterns and oxygen consumption in singing zebra finches

Song production in birds is driven by temporally complex respiratory patterns. In zebra finches (Taeniopygia guttata), song consists of repetitions of a stereotyped sequence of distinct syllables (motif). Syllables correspond to distinct expiratory pulses, which alternate with short deep inspirations. We investigated the effect of the song motor pattern on respiration using a newly developed mask system to measure oxygen consumption while simultaneously monitoring subsyringeal air sac pressure. The metabolic cost of song is closely related to song duration (mean=85.7 microl O(2) g(-1) x min(-1) over pre-song levels) and confirms earlier estimates for this species. When motif duration is controlled for, there is only small interindividual variability in oxygen consumption per motif. The oxygen measurements were also used to evaluate various methods of estimating and reporting the metabolic cost. Up to 20s before song, respiratory activity and oxygen consumption increased. Shortly before and during the introductory notes of the song bout, respiration and oxygen consumption decreased markedly. In some individuals, significant hyperventilation occurred during song, causing almost complete apnea after the song. In three different birds, we measured tracheal airflow and air sac pressure during song. Birds with higher airflow during song relative to flow during quiet respiration had a more pronounced decrease in respiratory activity after the song bout. These results suggest that gas exchange continues in the lung during the song bout and that long expiratory pressure pulses of the song motif can lead to hyperventilation but that no oxygen debt resulted from song. This research allows a first assessment of respiratory constraints that may influence the evolution of song complexity.