Highly significant effects of time (p<0.001) were detected for each trill feature ( Fig 8 ) except for trill entropy where a significant effect only was observed (p<0.05) and for the trill mean interval duration that did not change with time (p = 0.1903).
A possibly significant effect was only seen in one experiment on one measure (reduction of RMS power in the treated group).
However, a) there was already a numerical difference in song and syllables power before surgeries even if this difference did not reach statistical significance, b) this effect was not reproduced in the next two experiments, and c) most importantly, previous research never suggested that HVC might be implicated in the control of song power.