Zebra finches develop abnormal song if they cannot interact with adult song tutors during the 1st few months after hatching. The authors investigated whether untutored juveniles would learn song from each other. The birds were isolated from adult males at 10 days of age and their songs recorded after Day 80. By the authors' measures of syllable sharing and the judgments of human listeners, the songs of untutored brothers were as similar to each other as those of birds reared together with a tutor. The songs of group untutored birds were, however, more variable, and they contained abnormal elements, as did the songs of birds reared apart from all other males. The fact that untutored brothers copied song from each other raises the possibility that juveniles might influence each other's song development, even when adult tutors are present. If this were the case, it would increase the range of social interactions that determine which songs juveniles learn.