SummaryColour-banded populations of White-throatedCormobates leucophaea, Red-browedClimacteris erythropsand Brown TreecreepersCI. picumnuswere studied for up to six years in north-eastern New South Wales. All species are sexually dimorphic, insectivorous and nest in tree-holes. The White-throated and Red-browed are totally arboreal and nearly identical in size while the Brown spends half of its time on the ground and is about 50% larger than the other two species. The non-cooperative White-throated held small individual or pair territories which were vigorously defended but not stable over the study period. Offspring were evicted from the natal territory when independent and very few were seen again on the study sites. Cooperatively breeding Red-browed and Brown Treecreepers lived in pairs or groups which contained one breeding bird of each sex and up to three helpers. About one-quarter of the offspring of both species stayed on the study site for one year or more, and almost all were males. Helpers participated in nest construction, feeding of the incubating female, and feeding and defence of the young. Territories were larger, more static and less regularly defended than in the White-throated. Breeding success of the White-throated did not differ significantly from that of the Red-browed or Brown. However, within the latter two species, groups produced more young than pairs. Adult survivorship was higher in the Brown than in the White-throated where they co-existed. Survivorship of coexisting Red-browed and White-throated was similar, until the onset of a drought which had a greater negative effect on the latter. Group-living and cooperative breeding are probably related to specialised niche requirements and lack of suitable habitat in the patchily-distributed Red-browed, while in the widespread and semi-terrestrial Brown, predation appears to have played the major role. Roost-holes may be a limited resource for both cooperatively breeding species, favouring philopatry.