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 or P?rera in New Zealand.
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 (Rhymer & Simberloff 1996). 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 breeds in Indonesia, southern New Guinea and Australia, pelewensis on the southwest Pacific islands and northern New Guinea, and superciliosa 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 (Gillespie, 1985). 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 (Rhyner et al. 1994). The main reasons for displacement of the P?rera seem to be physical dominance of the larger mallards, combined with a marked population decline of the P?rera due to overhunting in the mid-20th century (Williams & Basse 2006)