Is the signal value of overlapping different from that of alternating during matched singing in Great Tits?

Interactive playback experiments to singing male Great Tits Parus major were used to compare the effects of overlapping their songs with alternating playback which avoided such overlapping. The results showed that the means of measures of approach response and amount of song sung did not differ significantly between the two treatments. However, the variation in song length (phrases/song) differed significantly, being largest during overlapping. The lack of overall differences in average response between the two treatments is evidence against the idea that males may escalate threat by changing from an alternating to an overlapping pattern of singing. On the other hand, the difference in variation in song length supports the idea and is in accordance with classical ethological theory that an escalation of threat will not necessary result in an increased counter threat, but rather in an increased variation of the counter threat. The variation in song length during overlapping may have resulted from test males using a number of different ways of responding to the escalated threat of overlapping.