Matched Counter‐singing Signals Escalation of Aggression in Black‐capped Chickadees (Parus atricapillus)

Abstract

AbstractBlack‐capped chickadees (Parus atricapillus) have the ability to shift their songs up and down over a wide range of absolute frequencies. Males can shift their songs over 465 ± 52.9 (SE) Hz. During the dawn chorus, males shift their songs by 80 Hz or more every 41 ± 8.8 (SE) songs, but it appears that males can sing at any frequency within their range. Frequency shifting may allow males to match counter‐sing with rival males; that is, to switch song output to match that of a rival. During simultaneously recorded dawn choruses, however, there was no correlation over time in the frequency of neighbouring males' songs, nor was there a correlation over time in the size of shifts between their songs. Moreover, males did not match the frequencies of songs presented on a played‐back tape at the edge of their territories during the dawn chorus. Matching was observed during some bouts of counter‐singing between males. In these cases, matched counter‐singing was highly associated with escalation of the conflict. We suggest that frequency matching in this species may be a graded signal that allows the singer to direct aggression towards a particular rival.