Blue-billed duck
Blue-billed duck | |
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Anseriformes |
Family: | Anatidae |
Genus: | Oxyura |
Species: | O. australis
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Binomial name | |
Oxyura australis Gould, 1837
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Range of Oxyura australis |
The blue-billed duck (Oxyura australis) is a small
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.
Distribution and habitat
The blue-billed duck is endemic to Australia's temperate regions.
The blue-billed duck is almost entirely aquatic. While they have been observed on land, they have difficulty walking,[2] exhibiting a penguin-like gait.[3] During non-breeding season, many ducks gather in flocks totalling several hundred,[8] especially juveniles and younger adults, in open lakes or dams in autumn and winter, far from the shore. For the rest of the year, during breeding season, the blue-billed duck prefers deep, freshwater swamps, with dense vegetation including cumbungi Typha orientalis (broadleaf cumbungi) and Typha domingensis (narrow-leaved cumbungi); although it has appeared in lignum swamps in more coastal areas,[2][3][9] especially in drier seasons.[7] They have also occasionally been found in large rivers and saline water bodies such as billabongs.[2][3]
Ecology and behaviour
The behaviour of O. australis depends on its breeding cycle. The ducks gather in large flocks on lakes during the winter while not breeding, although some mature adults remain in vegetative swamps and continue to breed. They will also fly more frequently, probably due to the open habitat, and escape threats by flying. While breeding, O. australis is secretive and wary,[10] and it will swiftly and quietly dive under water if threatened, resurfacing a large distance away, rather than escape by flying. The blue-billed duck has a low quack, which is seldom heard. The courting repertoire of the male is very complex and elaborative.[2][3][8] It includes such behaviour as rolling the cheek on the back, dab-preening (also sometimes performed by females), and sousing, where the head is thrown into the water in a prone position, and the back arched as if in spasm, with possibly the legs throwing spray above the body.[2][3] After the courtship ritual, and a vigorous chase, copulation follows with the female completely submerged. The birds then separate and preen themselves. In preparation for laying eggs, the female builds the nest, at which time the male will mostly desert the female.[2][3]
Diet
Oxyura australis is omnivorous, where invertebrates as well as seeds, buds, and
Reproduction
There is evidence that O. australis is partly migratory, with movement from breeding swamps of inland NSW to the Murray River during autumn and winter. Frith[2] claims O. australis is the most migratory of all Australian ducks. Marchant and Higgins[3] discredits this regular yearly migration, due to juveniles and young adults searching for new breeding grounds, especially on the fringes of the duck's range, with mature breeding adults often remaining. Indeed, experienced dominate adults are sedentary in breeding swamps[2][3] since migration would expend energy that instead would be used for breeding. Year-long sedentary adult breeding is confirmed by the observation that the laying period of ducks in captivity is continuous, reflecting “opportunistic breeding”.[3] Any variation in non-captive laying is in accordance to water-levels and hence abundance of food, a fact in contrast to Frith's description of reproduction being tied to the months between September and November.[3] Clutch size ranges from 3 to 12, the most common being 5 to 6, according to Marchant and Higgins.[3] Large clutch sizes indicate two females laying eggs in the one nest. It appears that a female will sometimes parasitise another's efforts at incubation, described as "facultative parasitism", by laying "dump clutches" in nests other than her own.[3] There is also some evidence of the duck laying its eggs in nests occupied by other water-birds.[9] The incubation is 26 to 28 days. After hatching, the young remain in the nest for one day, and are then led by the female from the nest. The young are relatively independent of the parents, being able to feed themselves immediately. The female will protect her brood, including hatchlings from dump clutches of other females.[3] At eight weeks, ducklings are of a similar size to the parents. Within one year, most have full adult plumage. Yearlings in captivity were observed to be able to breed.[3]
Conservation
Two substantial land uses combine to have a significant impact on the blue-billed duck. These are: the regulation of wetland ecosystems through drainage, flood mitigation and water harvesting; and vegetation loss due to clearing,
The blue-billed duck is listed as "threatened" on the Victorian
Relationship with humans
The health of wetland ecosystems can be determined by the abundance of waterbird species. A decline in bird numbers provides a warning that the natural ecological functioning of the freshwater system is at risk.[11][16] Despite short term gains for farmers through permanent flooding, sustainability of wetland systems would decrease. Any long-term decrease in the population of waterbirds such as O. australis, which continue to breed yearlong, irrespective of drought conditions by seeking out suitable habitat, would make excellent indicators for wetland health. Any long-term decrease in the duck's population would therefore be caused by habitat loss through factors such as salinity and overgrazing more so than drought.
Other comments
More field research is needed into the average lifespan of O. australis in the wild; although, based on the high number of eggs in a clutch, and maturing 12 months after hatching would indicate a short life span of less than 10 years. Captive ducks were still breeding at 16 years.[3] Further research into the accuracy of using O. australis as an indicator for habitat health, among other waterbirds, is needed, considering its ability to breed every season despite the effects of drought. Any long-term decrease in populations of O. australis would therefore more strongly reflect poor wetland ecosystem health, without the confounding effects of natural drought cycles.
References
- ^ a b BirdLife International (2022). "Oxyura australis". IUCN Red List of Threatened Species. 2022: e.T22679827A210733513. Retrieved 26 July 2022.
- ^ a b c d e f g h i j k l Frith H J (1977). Waterfowl in Australia. Angus and Robertson Sydney.
- ^ a b c d e f g h i j k l m n o p q r s t Marchant S, Higgins PJ, eds. (1990). Handbook of Australian, New Zealand and Antarctic Birds Volume 1: Ratites to Ducks. Oxford University Press, Melbourne.
- ^ BirdLife Species Factsheet
- ^ NSW National Parks and Wildlife Service. "Threatened Species Information: Blue-billed Duck Oxyura australis (Gould 1836)" (PDF). NSWNPWS. Archived from the original (PDF) on 5 September 2007. Retrieved 21 August 2007.
- ^ a b c d SWIFFT. "Blue-billed Duck". SWIFFT. Archived from the original on 22 July 2008. Retrieved 21 August 2007.
- ^ a b c d Department of Environment, Climate Change NSW (2005). "Blue-billed Duck – profile". Retrieved 25 August 2007.
- ^ a b Kingsford R (1991). Australian Waterbirds: A Field Guide. Kangaroo Press, Kenthurst.
- ^ a b The Waterbirds of Australia. The National Photographic Index of Australian Wildlife. 1985.
- ^ Trounson D; Trounson M (2001). Australian Birds Simply Classified (4th ed.). Smithfield, NSW: Gary Allen Pty Ltd.
- ^ a b c "Indicator: IW-33 Abundance and distribution of waterbirds". Australian Government: Department of Sustainability, Environment, Water, Population and Communities. Retrieved 1 June 2012.
- ^ COMLAW-Commonwealth of Australia Law (2006). "Declaration under s178, s181, and s183 of the Environment Protection and Biodiversity Conservation Act 1999 - List of threatened species, List of threatened ecological communities and List of threatening processes" (PDF). Retrieved 3 December 2008.
- ^ Department of Sustainability and Environment, Victoria Archived July 18, 2005, at the Wayback Machine
- ^ Department of Sustainability and Environment, Victoria Archived September 11, 2006, at the Wayback Machine
- ISBN 978-1-74208-039-0.
- ^ Catalyst (2002). "Waterbirds in Crisis". Australian Broadcasting Corporation. Retrieved 3 December 2008.
External links
- Media related to Oxyura australis at Wikimedia Commons