Pacific Black Duck
|Pacific Black Duck|
The Pacific Black Duck (Anas superciliosa) is a dabbling duck found in much of Indonesia, New Guinea, Australia, New Zealand, and many islands in the southwestern Pacific, reaching to the Caroline Islands in the north and French Polynesia in the east. It is usually called the Grey Duck in New Zealand, where it is also known by its Maori name, Pārera.
This sociable duck is found in a variety of wetland habitats, and its nesting habits are much like those of the Mallard, which is encroaching on its range in New Zealand. It feeds by upending, like other Anas ducks.
It has a dark body, and a paler head with a dark crown and facial stripes. In flight, it shows a green speculum and pale underwing. All plumages are similar. The size range is 54–61 cm; males tend to be larger than females, and some island forms are smaller and darker than the main populations. It is not resident on the Marianas islands, but sometimes occurs there during migration. The now extinct Mariana Mallard was probably originally derived from hybrids between this species and the mallard, which came to the islands during migration and settled down there.
There are three subspecies of Anas superciliosa:
- rogersi − Mathews, 1912 Australasian Duck, breeds in Indonesia, southern New Guinea and Australia
- pelewensis − Hartlaub & Finsch, 1872 – Island Black Duck, breeds on the southwest Pacific islands and northern New Guinea
- superciliosa Gmelin, 1789 − New Zealand Grey Duck, breeds in New Zealand
The New Zealand subspecies has declined sharply in numbers, at least in its pure form, due to competition from and hybridisation with the introduced mallard. Rhymer et al. (1994) say their data "points to the eventual loss of identity of the Grey Duck as a separate species in New Zealand, and the subsequent dominance of a hybrid swarm akin to the Mariana Mallard."
It was assumed that far more mallard drakes mate with Grey Duck females than vice versa based on the fact that most hybrids show a mallard-type plumage, but this is not correct; it appears that the mallard phenotype is dominant, and that the degree to which species contributed to a hybrid's ancestry cannot be determined from the plumage. The main reasons for displacement of the Pārera seem to be physical dominance of the larger mallards, combined with a marked population decline of the Pārera due to overhunting in the mid-20th century.
Various views and plumages 
- BirdLife International (2012). Anas superciliosa. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2.
- Rhymer, Judith M.; and Simberloff, Daniel (1996). "Extinction by hybridization and introgression". 83–109 27: 83. doi:10.1146/annurev.ecolsys.27.1.83.
- Madge, Steve; Burn, Hilary (1988). Waterfowl: an Identification Guide to the Ducks, Geese, and Swans of the World. Boston: Houghton Mifflin. ISBN 0-395-46727-6.
- Gillespie, Grant D (1985). "Hybridization, introgression, and morphometric differentiation between Mallard (Anas platyrhynchos) and Grey Duck (Anas superciliosa) in Otago, New Zealand". The Auk 102 (3): 459–469.
- Rhymer, Judith M.; Williams, Murray J.; and Braun, Michael J (1994). "Mitochondrial analysis of gene flow between New Zealand Mallards (Anas platyrhynchos) and Grey Ducks (A. superciliosa)". The Auk 111 (4): 970–978. doi:10.2307/4088829.
- Williams, Murray; and Basse, Britta (2006). "Indigenous gray ducks, Anas superciliosa, and introduced mallards, A. platyrhynchos, in New Zealand: processes and outcome of a deliberate encounter". Acta Zoologica Sinica 52 (Supplement): 579–582.
Further reading 
- Heather, Barrie D.; and Robertson, Hugh A. (1996). The Field Guide to the Birds of New Zealand. Auckland: Viking. ISBN 0-670-86911-2.
|Wikimedia Commons has media related to: Anas superciliosa|
|Wikispecies has information related to: Anas superciliosa|