Feet are small and weak, suitable for grasping a perch and little else. When landing to rest they flutter up to a twig or wire top grasp it with their feet. Apart from shuffling they can barely move on their legs.
Crown to mid-back is glossy blue-back; flight feathers and the shallow forked tail are more dusky. Rump is off-white, forehead is buff or pale orange. Under-parts are off white. Finely streaks of grey on the throat; eye is brown, bill black, feet flesh-grey. Male and female are similar in appearance, immature birds lack the glossy surface on the back and have duller foreheads.
Spends most of the day on the wing feeding on insects gathered over water; they will dive down to pick up an insects floating on the water surface.
Breeding takes place from July to January in loose colonies. Nest is usually in a tree hole, but holes in cliffs and in city buildings have been used. Sometimes a single entrance leads to several nest chambers. If the entrance is too large or nesting ledges inside a hollow trunk too flat mud may be used to alter the shape to suit the bird's preferences. The same nests are used year after year. The base is usually lined with small dried leaves, sometimes with feathers and grass. Three to five eggs are laid; dull white, speckled with brown and mauve; oval. About 18 by 13 millimetres. Incubated by both parents for about 15 or 16 days.
When roosting, large flocks circle as the light fades then dive to roost simultaneously in swamps or dive individually into their nesting hollows.
Found throughout Australia in wooded habitats; regular migrants within the continent. In spring they spread out south of the Tropic of Capricorn and in Tasmania to breed preferably in large trees near water. In autumn most, but not all, birds move north; large flocks gather in open areas, sometimes perched on telephone and fence lines, before heading off sometimes spreading through northern Australia into the east Sunda area in Indonesia.