WatchList Species Account for Hawaiian Duck (Anas wylvianna)

Qualifies for the list as a Red List Species


Hawaiian Duck by Bill Hubick

Photo: Michael Walther

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 Kaua'i and Ni’ihau but is reintroduced on Oahu, Hawaii and Maui. Its persistence on Kaua'i was apparently due to the fact that this island is the only one on which the mongoose has not become established.


Habitat for this duck includes wetlands, coastal ponds, swamps, mountain streams, flooded grasslands, aquaculture ponds, flooded fields, and occasionally boggy forests, as high as 10,800 feet.


Most pairs nest along montane streams, ideally at 400 to 4,000 feet in elevation, with swift-flowing clear, shallow water, strewn with boulders and potholes, and bordered by high, heavily vegetated banks. A dabbling duck, the species feeds in shallow water along the edge of streams and wetlands and grazes on upland grasses near water or flooded pastureland, taking aquatic invertebrates and plants, plus seeds and grains.


Invasion by alien plants can negatively affect its wetland habitats, and outbreaks of botulism have killed many individuals. The biggest threat to the bird as a viable species ishybridization 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 Kaua'i 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 succeedif the hybrids and all remaining Mallards are removed beforehand.


On Kaua'i, the Hanalei National Wildlife Refuge is an important sanctuary for the birds. Wetlands on Kaua'i have been created and managed for endangered waterbirds and are used by theduck for foraging and breeding. Protection of the duck on Kaua'i is essential, especially considering these are genetically pure birds.