Figure 4.

Behavioral factors and song tempo. A, C, E, Means and SEs across birds. B, D, F, Pearson's coefficients by bird for each relationship indicated directly to the left. Pearson's marked * are significant with p < 0.05. A, Song tempo by time of day in hourly bins. B, Strength of tendency for songs to speed up in the first 4 h after lights on (white bars) and slow down between hours 5 and 11 (black bars). C, Acoustic activity by hour of day. D, Tendency for activity to decrease over the afternoon beginning at hour 6. Acoustic activity was defined as the number of recordings per min in a 30 min window centered on each song. E, F, The relationship between sequence length deviation and acoustic activity binned in integers. Song tempo changes systematically during the course of the day and may be influenced by factors correlated with overall arousal.