Hawaiian Duck

Anas wyvilliana

Description

The Anas wyvilliana (Hawaiian duck) is a dark brown mallard also known by the Hawaiian name "koloa." It probably evolved from stray migratory ducks that remained in Hawaii as year-round residents. Mallards range generally from 20-28 in (50-71 cm) in body length, although the Hawaiian duck is noticeably smaller than its mainland counterpart. Unlike the mallard, both sexes of the Hawaiian duck are similar in appearance, resembling a dark female mallard. The larger male typically has a darker head and neck, with an olive-colored bill; females have orange bills. The Hawaiian duck is closely related to the Laysan duck (Anas laysanensis ) and the Mariana mallard (A. oustaleti ). The species, first described in 1852, has since been variously classified as a subspecies of either the mallard or the New Zealand gray duck. The American Ornithologists Union now lists it as a full species.

Behavior

The Hawaiian duck is typically found alone or in pairs, although larger numbers of birds occasionally congregate around a rich food source. It is very wary of outside disturbance, particularly when nesting or molting. It feeds on snails, dragonfly larvae, earthworms, grass seeds, and other plant matter. While a strong flyer, the Hawaiian duck it does not range far from its narrowly defined home territory and rarely moves between islands. Nests are built on the ground near water at any time of the year; peak breeding season is from December to May. The female lays a clutch of two to 10 eggs that she incubates for about 30 days. Most chicks hatch during April, May, and June.

Habitat

The Hawaiian duck adapts to a wide range of wetland habitats, including freshwater marshlands, flooded grasslands, coastal ponds, streams, mountain pools, mountain bogs, and forest swamps at elevations from sea level up to 8,000 ft (2,400 m).

Distribution

The Hawaiian duck was known from all the main Hawaiian Islands except Lanai and Kahoolawe. Although there are no estimates of the original population, it is likely that this bird was once fairly common. Indiscriminate hunting in the late 1800s and early 1900s took a heavy toll on the Hawaiian duck, whose numbers fell drastically until the mid-twentieth century. In 1949, only about 500 birds remained on Kauai, an unknown number on Niihau, and about 30 on Oahu. It was then considered only an occasional visitor to the island of Hawaii, having already been eliminated from Maui and Molokai. It was apparently extirpated on Oahu in 1960 when Kaelepulu pond, the last nesting site on the island, was modified as part of a housing development. By the 1960s the Hawaiian duck was found only on Kauai. The Hawaiian duck has been reintroduced to the coast of the island of Hawaii from Hawi south to Paauilo. A natural population on Kauai has remained stable. Estimates from the mid-1960s indicated approximately 2,000-3,000 birds, mostly in remote, mountainous stream areas. A population of about 50 birds has been established on Oahu in typical waterfowl wetland habitat. Three hundred birds were released on Oahu at Kawainui Marsh, Naupia Ponds, Waimea Falls Park, and Hommaluhia Park. Although the Kauai population of Hawaiian duck exceeds 2,000 birds and is self-sustaining, U.S. Fish and Wildlife Service (FWS) goals for de-listing the species call for self-sustaining populations of 500 birds on Oahu and the island of Hawaii.

Threats

The Hawaiian duck was historically threatened by hunting, although this is no longer the case. Its most important recent and ongoing threat is the loss of wetland habitat through conversion into agricultural, commercial, or residential land-uses. Also important are the effects of genetic "pollution" (or introgression) by hybridization with introduced mallards; predation of eggs and birds by introduced mammals (especially mongooses, domestic cats, dogs, and rats); damage to vegetation and other elements of habitat by introduced ungulates (such as cows and deer); and the invasion of wetlands by alien plants and fish. Introduced diseases, and possibly the effects of pollutants, may also be significant stressors. The population of wild Hawaiian ducks in the late 1990s was about 2,500 birds.

Conservation and Recovery

The most important actions necessary in support of the Hawaiian duck are the protection of its remaining wetland habitats. The conversion of wet-lands into hostile land-uses (for example, into agricultural or residential uses) must be slower or stopped. It is also necessary to control the abundance of alien species that are predators of the rare duck, or that damage its habitat. Feral populations of mallards should be eliminated within the range of the Hawaiian duck. The FWS is preparing a Recovery Plan for the endangered Hawaiian duck.

Contacts

U.S. Fish and Wildlife Service
Pacific Islands Ecoregion
300 Ala Moana Boulevard, Room 3-122
Box 50088, Honolulu, Hawaii, 96850
Telephone: (808) 541-3441
Fax: (808) 541-3470

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Reference

Honolulu Zoo. 2000. "Koloa (Hawaiian Duck)." http://www.honoluluzoo.org/koloa_duck.html