GREY  DUCK

The critically threatened grey duck Anas superciliosa superciliosa, also known as parera, is an endemic dabbling duck, the New Zealand subspecies of Pacific black duck.  It belongs to the Anatidae family of swans, geese and ducks, which is part of the Anseriformes order.

Grey duck were commonly found in shallow wetlands and fresh water streams, and occasionally in estuaries throughout New Zealand until the 1950s. They have suffered severely from loss of habitat, and competition with the introduced mallard duck Anas platyrhynchos.

The subspecies A. superciliosa rogersi breeds in Australia, Indonesia and southern New Guinea; and A. superciliosa pelewensis breeds in northern New Guinea, and on southwest Pacific islands as far north as the Caroline Islands and Tahiti to the east.

Above: Grey duck Anas superciliosa superciliosa
Photo: C.D. Roderick, Crown Copyright © Department of Conservation.

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The Chatham Islands are a stronghold for the New Zealand subspecies, as there appears to be a lower level of hybridisation with mallard ducks.  Although now thinly scattered throughout the mainland, more prominent populations are found in the Northland, Waikato, Gisborne and Westland regions.

A distinguishing feature is a pattern of stripes extending from the bill back onto the head, with a thick dark patch over the top of the head, a thinner brown stripe through the eye, and another fainter line below from the beak opening.  The three dark stripes alternate with cream coloured stripes either side of the dark eye stripe.

Males and females are alike in appearance, and similar to plumage of the female mallard. The grey duck's colouring is darker overall, and the head stripes more pronounced than the female mallard.

Introduced mallards have taken over from grey duck, comprising 80 percent of New Zealand's dabbling duck population.

Grey duck have a white underwing and an iridescent turquoise green speculum on their wing (lower right), whereas the mallard speculum is blue or purple.  The blue speculum tends to predominate on hybrids.

The grey duck's legs and feet are greenish brown, but the legs of hybrids tend to be orange-brown, taking on the color of the mallard's legs.

A grey duck's diet is typical of a dabbling duck - mostly aquatic snails and invertebrate insects, leaves and seeds of aquatic plants, and caterpillars and worms on pasture.

During the period from September to December they nest on the ground in dense grass cover or in a tree hollow, sometimes as far as 2 km from the feeding territory.

Four to nine eggs are laid, one each day, and packed in down while the female returns to the feeding area once or twice a day during the 26-28 day incubation period. The male takes off after 5 days to mate again.

Genetic pollution from mallard ducks

The mallard was first introduced into New Zealand from Europe in the 1860s but failed to acclimatise. After eggs were imported in 1930 from California, the population multiplied so quickly that mallards are now regarded as an invasive species.

Mallards breed throughout Europe, Asia, North America, New Zealand and Australia.  It is the ancestor of all domestic ducks belonging to the subfamily Anatinae, with the exception of a few species derived from the Muscovy duck Cairinia moschata.

Mallards can cross-breed with 63 duck species, causing a serious worldwide threat to the genetic integrity of native waterfowl.  Eventually, hybrids ranging between species will reverse the speciation that has previously occurred over a very long period.

In addition to hybridisation with New Zealand grey duck, mallard interbreeding is polluting the genes of its descendent relatives, the American black duck, Hawaiian duck, Meller's duck, Florida duck, Mexican duck and yellow-billed duck which are endemic to their local regions.

The now extinct Mariana mallard Anas oustaleti was endemic to the Mariana Islands (which include Guam) in the Northwest Pacific Ocean. This species was possibly the result of hybridisation speciation between Anas superciliosa and mallard Anas platyrhynchos which migrated to the Marianas. A. oustaleti is not recognised as a species by IUCN and is sometimes regarded as a subspecies of mallard, or Pacific black duck A. superciliosa.

Despite its' rapid decline and 'nationally critical' threatened status, the grey duck is still a game bird.