The Pacific black duck was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.

[3][4] The naturalist Joseph Banks had provided Latham with a water-colour drawing of the duck by Georg Forster who had accompanied James Cook on his second voyage to the Pacific Ocean.

[9] 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.

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.

Food is obtained by 'dabbling', where the bird plunges its head and neck underwater and upends, raising its rear end vertically out of the water.

[14] The Pacific black duck has declined sharply in numbers in New Zealand and several Australian islands due to competition from and hybridisation with the introduced mallard.

[15] 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."