Does song overlap signal aggressiveness? An experimental study with repeated measures in free-ranging great tits

Vocal communication is often used to signal willingness escalate into a physical fight during territorial conflicts. In songbirds, starting sing when an opponent already sings (song overlapping) has been suggested aggressive intent (willingness escalate). We multiyear data set test whether song overlapping predicts aggressiveness in great tits, Parus major. Territorial males were subjected twice simulated intrusion their mate was the egg-laying phase, and she incubating. Males presented with taxidermic mount noninteractive playback of conspecific near nestbox. The experiment conducted over 3 consecutive years, resulting repeated measures for that bred across multiple years. estimated minimum approach distance intruder, repeatable heritable trait likelihood attack, as measure aggression. determined duration by focal male relative values expected chance. Against expectations, we found birds overlapped less (rather than more) aggressive. addition, variance partitioning demonstrated this link resulted from within-individual effect: became one observation next, they also more. There no among-individual individuals on average more did not, average, overlap either or others. Our results thus imply linked aggression but opposite not among individuals. Furthermore, majority at below chance levels. Overall, may rather ‘nonengagement’, result interference avoidance, allowing residents better hear intruder's acoustic output intrusions.