SummarySuperb Blue Wrens,Malurus cyaneus, were subjected to experimental territory infringement by means of models—prepared skins mounted in a life-like manner. Only the dominant male in the group showed aggression during winter, hut all mature members of the group (which may include more than one male) responded during nesting.When models ofMalurusspecies, other thanM. cyaneus.were presented, the initial reaction was usually negative. However, after aggressive experience with a model of its own species.M. cyaneusreadily responded to models of these other dose relatives Field observations on mixed populations showed that no fighting occurred between these sympatric species.