The nominate subspecies of the Pacific Black Duck is called the Grey Duck in its native New Zealand. Other subspecies live in Australia, Indonesia and the Pacific islands.
Duck and drake have similar plumage and can be distinguished from the introduced Mallard (with which they interbreed) by a green instead of blue speculum (wing-bar).
There has been a massive decline in population partly due to hunting and partly to the increase in hybrids with the Mallard. (New Zealand also has a "Grey Teal" with a green speculum.)
The Australian subspecies of the Pacific Black Duck above,
Anas superciliosa rogersi, also called the Australian/Australasian Black Duck, inhabits Australia and some of New Guinea and Indonesia.
This Pacific Black Duck appears to have a blue speculum rather than green. (Also shows the lightish yellow legs of the species.)
Pacific Black Duck x Mallard hybrid