A typical reed finch, the Chestnut-breasted Mannikin flocks in groups of up to several hundred birds. They bunch into tight-flying packs, calling and executing all manoeuvres in rapid unison. They also feed, drink, rest, sleep and sing together; fighting is rare but ritualized. They do not preen one another and never build roost nests, clustering instead to sleep in brakes of reeds. Bonds and coherence in flocks are kept by ‘jingling’ and peering.
Chestnut-breasted Mannikins inhabit banks of rank grasses and reeds on the margins of swamps, mangroves and rivers around northern and eastern coastal Australia. There they are locally nomadic, more so in the northwest than the east.
They mostly eat half-ripe grass seeds, gathering while clambering nimbly among seeding stems, one foot after the other. They land among the upright stems, reach out of a laden spike, pull it down and clump it with one foot while they pick out the seeds. At the start of breeding season they also catch flying termites on the wing. Drinking is by scooping, they birds tilting their heads back to swallow.
The Chestnut-breasted Mannikin breeds all months but mainly in summer and autumn. They build a spherical nest compressed at side with dry blades of grass, that somewhat resembles a bottle on its side with nest sloping downwards. They line it with fine grass stems. They build their nests within 2m of the ground in dense clumps of grass and reeds or bushes. 4-6 eggs are laid and incubated by both sexes for 12-13 days.