Behavioural Significance of Duet Interactions: Cues From Antiphonal Duetting Between Males (Cossypha Heuglini H.)

Antiphonal duetting is regarded as a formalized interaction display between, usually mated, individuals of different sex. Proceeding from observations that antiphonal duetting can also occur between male conspecifics, we investigated the structure and context dependance of the display in aviary kept male robin chats (Cossypha heuglini H.). In the male/male duets, which were confined to a particular dyad of our tests subjects, all characteristic features corresponded to those of the male/female display (Fig. 1). Duet roles were not exchanged between males, and the "female" contribution was exclusively delivered by the younger male. Duetting obviously influenced both, interactions within the dyad (in terms of inhibiting overt aggression) and the territorial behaviours (attacks, chases) towards third introduced conspecifics. During confrontation with such males, the duetters took different roles in attempting to deter an outsider (test 3), which were similar to those observed for mated individuals of a pair. In tests where only one individual could attack, duet rates and attack rates were positively related (Fig. 4). Preceding a duet performance, one male approached the other one (Fig. 3), and restriction of such proximity (tests 1s, 2s) lowered both, duet rates and attack rates against an introduced male (Fig. 4 & 5). Our results allow to discuss relationships between duet behaviour and alliance formation in our males. To our knowledge such a cooperation, though presumably temporary, has not been described for adult males of highly territorial bird species.