WatchList Species Account for Hawaiian Duck (Anas wylvianna)

Qualifies for the list as a Red List Species

Photo: Bill Hubick

Common in the 19th Century, by 1962 the Hawaiian Duck was down to fewer than 500 individuals. Its decline was due to the destruction of key wetland habitats and to predation from introduced mammals such as cats, dogs, and mongooses. It was still hunted into the 1930s, another factor in its decline. Once found on all the main Hawaiian Islands, it is now only on Kauai and Ni’ihau but is reintroduced on Oahu, Hawaii and Maui. Its persistence on Kauai was apparently due to the fact that Kauai is the only one of the wet islands on which the mongoose has not become established.

Habitat for the duck includes wetlands, coastal ponds, swamps, mountain streams, flooded grasslands, aquaculture ponds and flooded fields, and occasionally boggy forests, as high as 3,300 m. Most pairs nest along montane streams. Optimal streams for nesting are at 150 to 1,220 m elevation, 7 m wide, with swift-flowing clear, shallow water, and strewn with boulders and potholes, bordered by high, heavily vegetated banks. A dabbling duck, the bird feeds on aquatic invertebrates, aquatic plants, and seeds and grains. It feeds in shallow water along the edge of streams and wetlands and grazes on upland grasses near water or flooded pastureland. Invasion by alien plants can negatively affect its wetland habitats, and outbreaks of botulism have killed many individuals. But the biggest threat to the bird as a viable species is hybridization with feral Mallards, which have corrupted the populations on Oahu and Maui.

The total population is estimated at 2,200, of which 2,000 pure birds are on Kauai and 200 on the island of Hawaii, with 300 hybrids on Oahu and 50 hybrids on Maui. Reintroduction on the latter two islands will only succeed if the hybrids and all remaining Mallards are removed beforehand. On Kauai, the Hanalei National Wildlife Refuge is an important sanctuary for the birds. Wetlands on Kauai have been created and managed for endangered waterbirds and are used by the duck for foraging and breeding. Protection of the bird on Kauai is essential, especially considering these are genetically pure birds.