These are a small water bird found throughout Australia and the Pacific region, they have also self-introduced to New Zealand. Their preferred habitats are still, shallow, weedy, freshwater wetlands, dams and ponds, here the easiest place to see them is at the Emu Park Wetlands.
They feed on the surface and underwater on small aquatic animals such as snails, fish, insects and their larvae, and crustaceans, and they can often be seen diving repeatedly for food. When threatened instead of flying away they dive under water and, after a surprisingly long period, resurface some way off.
The birds in the photo are in breeding plumage, non-breeding plumage of both sexes is dark grey-brown above and mostly silver-grey below. As you can see in the photo the nest is a floating damp platform of waterweeds, usually anchored in shallow water, and when sitting birds leave the nest they cover their eggs before slipping off into the water, they may raise up to three successive broods in a season. The striped downy chicks are able to swim from birth and are cared for by both parents, when the parents start breeding again the young of the previous brood are driven away.