Blue billed duck
The blue-billed duck (Oxyura australis) is a small Australian stiff-tailed duck, with both the male
and female growing to a length of 40 cm (16 in).[2][3] The male has a slate-blue bill which changes
to bright-blue during the breeding season, hence the duck's common name. The male has deep
chestnut plumage during breeding season, reverting to a dark grey. The female retains black
plumage with brown tips all year round. The duck is endemic to Australia's temperate regions,
inhabiting natural inland wetlands and also artificial wetlands, such as sewage ponds, in large
numbers. It can be difficult to observe due to its cryptic nature during its breeding season through
autumn and winter. The male duck exhibits a complex mating ritual. The blue-billed duck is
omnivorous, with a preference for small aquatic invertebrates. BirdLife International[1] has
classified this species as Least concern. Major threats include drainage of deep permanent wetlands,
or their degradation as a result of introduced fish, peripheral cattle grazing, salinization, and
lowering of ground water.
Taxonomy
The blue-billed duck was described in 1836 by ornithologist John Gould. The specific name
australis is derived from the Latin for "southern", hence Australian.
Description
The tail feathers for both the male and female are made up of thick, spine-like shafts. The tail is
usually held flat on the surface of the water, or held erect when defensive. The male also holds the
tail erect during courtship displays. The feet are quite powerful, which aids in swimming and
diving. The duck sits low in the water in comparison to other ducks.[2] During breeding season,
apart from the aforementioned bright-blue bill, the male's head and neck are glossy black, and the
back and wings are a rich chestnut. During the non-breeding season, the head changes from its
glossy black to black with grey speckles, and its body changes from chestnut to dark grey.[2] Some
males retain breeding plumage throughout the year.[3] The female's plumage does not change
throughout the year. Its head is dark brown, and the back and wings consist of black feathers with a
light-brown tip, giving a mottled appearance, although the National Parks and Wildlife
publication[5] on O. australis refers to bands on each feather rather than a single feather-tip
colouration. The female blue-billed duck has a dark grey-brown bill and grey-brown feet, while the
male's feet are grey. Both males and females have brown irises. Juvenile blue-billed ducks have a
resemblance to adult females but appear paler and have a grey-green bill.