This paper presents the acoustic features and the behavioural context of the unison call of the East African Crowned Crane Balearica regulorum gibbericeps. It speculates on the different functions of the unison call according to the situations where it is given. This is tested with the appeasement-threat hypothesis, which claims that the threatening acoustic characteristics of the unison call should be enhanced if it is given as a territorial call. In comparison, the appeasing acoustic characteristics should be stronger if the unison call is performed at flock sites where it possibly serves for mate assessment.
vocalization, Grey Crowned Crane, Balearica regulorum, unison call, captive breeding