Differences between the mean rate of O₂ consumption during song and the mean rate of O₂ consumption () immediately before song bouts.

<p>In one bird (G16), song amplitude and background noise condition were significantly correlated with differences between pre-song and during-song levels. The remaining two birds (G62 and G68) pre-song to during-song differences were not correlated with background noise treatment or song amplitude. Data points show mean difference between pre-song and during-song levels, error bars indicate 95% confidence intervals (* indicates significance at p<0.001 levels, see text for details).