Grey duck Anas superciliosa superciliosa

Grey duck

Description

  • Grey duck have become one of New Zealand’s most threatened bird species due to extensive hybridisation with the superabundant introduced mallard. The extent of hybridsation makes it very difficult to determine whether the bird in question is a ‘true’ grey duck, or a hybrid female (see online reference below to assist identification).
  • Grey duck males and females are largely alike. The species is uniformly darkish brown. The most striking feature is the facial colouration; the top of the head is almost black, and the face cream, with two bold, black stripes across the face, one going across the eye. The eye is dark brown and the bill is dark grey.

Interesting Facts

  • Grey duck are found throughout Australasia, including Indonesia and the Pacific.
  • Grey duck used to comprise 95% of New Zealand’s dabbling duck population in the 1960s, and numbered c.1.5 million in 1970. However, the self introduction of the mallard has seen an extraordinary decline in their abundance as the two species have interbred. Offspring of the two species are paler and have less distinct facial stripes.
  • It is thought that within a short timeframe, pure bred grey ducks may become extinct within New Zealand. Some believe that there are likely to be few, if any, pure-bred grey duck remaining. Isolated populations of grey duck may be the most ‘pure’ birds remaining. However, small populations that appear characteristically ‘grey duck-like’ are known from some urban areas (e.g. Waikanae, Kapiti Coast). The highest proportions of ‘grey duck-like’ birds are found in Northland and the West Coast.
  • The hybrid form, grey duck × mallard, has recently been given its own threat classification of ‘Not Threatened’.
  • All wetland birds require high quality wetland habitat buffered from the effects of surrounding land management.

Association with Plantations

  • Wetland birds are found in many plantation forests.
  • Wetland birds may be hard to detect due to their elusive behaviour.

Threats

  • Habitat loss and degradation from wetland drainage, loss of riparian margins, and the effects of surrounding land use.
  • Invasion of exotic plants, which can seriously modify wetlands and reduce suitability for birds.
  • Disturbance and motor wash from recreational boats.
  • High predation rates, particularly of pateke mainly from dogs, cats and mustelids.
  • Mammalian predation may also affect some other wetland bird species, but the extent of the impacts is unknown.

Management Options and Methods

  • Habitat protection:
    • Protect important wetland habitats and riparian buffers.
    • Avoid using herbicides or pesticides close to wetlands.
    • Ensure weeds are not inadvertently introduced to wetlands, e.g. via machinery or boats.
    • Consider control options for existing, invasive, wetland weeds.
    • Consider a staged removal of willows to ensure ongoing cover for crakes and ducks.
  • Forest operations:
    • Minimise damage to riparian and wetland habitat during road construction and harvest operations.
    • Avoid grazing wetlands and their margins. Fencing may be appropriate in some situations.
    • Avoid diverting run-off into wetlands.
    • Minimise disturbance during spring breeding.
    • If grey duck are present, discuss predator control with neighbours and DOC.
  • Injured or dead wetland birds (particularly the more threatened species, i.e. white heron, bittern and pateke):
    • Place injured birds in a cardboard box (keep shaded) and deliver to a local vet, SPCA, DOC.
    • Call DOC if bird is dead.

Monitoring Options

  • Increase staff and contractor knowledge about wetland birds.
  • For important wetlands that are likely to have the more threatened species, consider undertaking a bird monitoring programme:
    • Counts of pateke flock sites in late summer.
    • Fernbirds, spotless crakes and to a lesser extent marsh crakes and banded rails respond to taped playback calls.
    • The booming calls of bittern are characteristic at dusk in September-October particularly during bright moonlight.
  • Maintain a database of sightings.

Further Information and Support