SUMMARYBell, H. L. 1980. Composition and seasonality of mixed-species feeding flocks of insectivorous birds in the Australian Capital Territory. Emu 80: 227–232.Data are presented on 105 mixed-species feeding flocks of insectivorous birds on Black Mountain, ACT. About half of the sixty-nine species present participated in flocks, with an average of about four species per flock. Flocks were dominated by species that themselves form flocks and up to five such species were present at one time. Marked seasonal change occurred, with flocking activity greatest in winter and lowest in the spring breeding season. Individual species also displayed seasonal differences in participation. The generaAcanthizaandMalurusappear to behave as nucleus species, round which flocks are formed.