 A ' corroboree ' ( from the word for a ceremonial meeting of Aboriginal Australians ) is a group display where birds converge on adjacent branches and simultaneously pose <unk> , giving wing @-@ waving and open @-@ bill displays and the yammer call . A corroboree occurs when birds meet after a change in the social environment , such as a bird returning after an absence , or the <unk> of an intruder , or the coming together of different coteries . The corroboree appears to have a bonding function , and may involve all members of a colony . 
