[order] ANSERIFORMES | [family] Anatidae | [latin] Oxyura australis | [authority] Gould, 1836 | [UK] Blue-billed Duck | [FR] Erismature australe | [DE] Schwarzkinn-Ruderente | [ES] Malvasia Australiana | [NL] Australische Stekelstaart
The stiff-tailed ducks are part of the Oxyurinae subfamily of ducks. All have, as their name implies, long stiff tail feathers, which are erected when the bird is at rest. All have relatively large swollen bills. These are freshwater diving ducks. Their legs are set far back, making them awkward on land, so they rarely leave the water. Their unusual displays involve drumming noises from inflatable throat-sacs, head throwing, and erecting short crests. Plumage sequences are complicated, and aging difficult. Plumage is vital for survival because of this animals tendency to spend time in the water. Without plumage this duck would die of hypothermia because of an inability to regulate its body temperature. A fossil species from the Late Pliocene or Early Pleistocene of Jalisco (Mexico) was described as Oxyura zapatanima. It resembled a small Ruddy Duck or, even more, Argentine Blue-bill. A larger Middle Pleistocene fossil form from the southwestern USA was described as Oxyura bessomi; it was probably quite close to the Ruddy Duck.
The Blue-billed Duck is one of only two Australian species of stiff-tailed ducks – diving ducks with spine-like tail-feathers. It is a small and compact duck, with a length of 40 cm. The male’s head and neck are glossy black, and the back and wings are a rich, chestnut to dark-brown. During the summer breeding season the male’s bill turns bright blue. The female is brownish-black above, with narrow bands of light brown and mottled light brown and black below. The female’s bill is dark grey-green. In the non-breeding season the male resembles a dark female. The tail is usually held flat on the water, although during courtship, or when alarmed, it is held fully erect.
Australasia : Australia. Oxyura australis occupies permanent deep water-bodies in southern Australia with the population estimated at about 12000 mature individuals, or about 15000 birds overall. The species is found particularly in the Murray-Darling basin and southern Victoria.
The Blue-billed Duck prefers deep water in large permanent wetlands and swamps with dense aquatic vegetation. The species is completely aquatic, swimming low in the water along the edge of dense cover. It will fly if disturbed, but prefers to dive if approached. During autumn and winter the species aggregates in large flocks but disperses to smaller waterbodies when breeding. Aggregations also occur during drought.
Blue-billed Ducks usually nest solitarily in Cumbungi over deep water between September and February. They will also nest in trampled vegetation in Lignum, sedges or Spike-rushes, where a bowl-shaped nest is constructed. The most common clutch size is five or six. Males take no part in nest-building or incubation. Young birds disperse in April-May from their breeding swamps in inland NSW to non-breeding areas on the Murray River system and coastal lakes.
Blue-billed Ducks will feed by day far from the shore, particularly if dense cover is available in the central parts of the wetland. They feed on the bottom of swamps eating seeds, buds, stems, leaves, fruit and small aquatic insects such as the larvae of midges, caddisflies and dragonflies.
copyright: Nick Talbot
This species has a moderately small population and is therefore classed as Near Threatened. It faces a number of threats and the population may be smaller than currently estimated. If it is found that the population size is very small and declining, the species may qualify as threatened.
It is threatened by drainage of deep permanent wetlands, or their degradation as a result of introduced fish, peripheral cattle grazing, salinisation and lowering of ground water. A small number are probably shot by accident during the duck hunting season. The western population is particularly threatened with predictions that rainfall there will fall as temperatures rise. In 2007, there was an ongoing drought in the species’s range
Blue-billed Ducks are partly migratory, with short-distance movements between breeding swamps and overwintering lakes with some long-distance dispersal to breed during spring and early summer.