Pacific grey duck / Pacific black duck

Anas superciliosa

Wenkbrauweend / Augenbrauenente / Canard à sourcils

The Pacific black duck 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.

Several subspecies of Anas superciliosa described:

• 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
• rukensis generally synonymized with pelewensis
  

In view also of extensive hybridization, it seems unwise to persist in recognizing subspecies (Rhymer, J.M., Williams, M.J. & Kingsford, R.T., 2004). Treated as monotypic.

Above: adult male

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.

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend is not known, but the population is not believed to be decreasing sufficiently rapidly to approach the thresholds under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern (IUCN, 2012).

The species currently has a large global population estimated to be 180,000-1,200,000 individuals (Wetlands International 2006). Both superciliosa and rogersi have undergone significant declines in the last 20 years (Marchant and Higgins 1990). In New Zealand, the superciliosa population was estimated at 1.5 million birds in 1970, decreasing to 1.2 million by 1981, and less than 500,000 in the 1990s (Heather and Robertson 1997). A second estimate placed numbers at between 80,000 and 150,000 in 1993 (Rose and Scott 1997). Subspecies pelewensis was estimated at 10,000-25,000 birds and is considered stable (Rose and Scott 1997).

The species is believed to be declining throughout its range due to a combination of competition and hybridisation with Mallards (Anas platyrhynchos) (Heather and Robertson 1997). This introduced species is most common in developed areas and, in New Zealand at least, numbers are still increasing (Marchant and Higgins 1990). Also in New Zealand, loss of wild habitats is considered to be a leading cause in declines (Heather and Robertson 1997), and there is a slow decline through Melanesia due to hunting and habitat degradation (G. Dutson in litt. 1999). Such habitat destruction is also occuring in Australia, but birds there have proved to be more able to utilise artificial habitats (Marchant and Higgins 1990).

Above: adult female

Above: adult male

Above: adult female

Above: adult female

Above: adult female and a duckling at their nest

Above: adult pair with ducklings, female in background

Above: adult ducks

Above: Mallard-types from Asia and Australia. Click to enlarge.