The Hawaiian duck (Anas wyvilliana) or koloa is a species of bird in the family Anatidae that is endemic to the large islands of Hawaii. Taxonomically, the koloa is closely allied with the mallard (A. platyrhynchos). Recent analyses indicate that this is a distinct species that arose through ancient hybridization between mallard and the Laysan duck (Anas laysanensis). The native Hawaiian name for this duck is koloa maoli (meaning "native duck"), or simply koloa. This species is listed as vulnerable by the IUCN Red List of Threatened Species, and its population trend is increasing. On average, the male weighs and the female weighs .

Diet

Hawaiian ducks are "opportunistic feeders". Their diet consists of freshwater vegetation, mollusks, insects, and other aquatic invertebrates. Specifically, they are known to consume snails, insect larvae, earthworms, tadpoles, crayfish, mosquito larvae, mosquito fish, grass seeds, rice, and green algae.

Vocalization

The Hawaiian duck quacks like a mallard, but its call is softer and it quacks less frequently. They are very secretive birds and do not associate with other animals.

Reproduction

Some pairs nest year-round, but the primary breeding season is from December to May, during which pairs often engage in spectacular nuptial flights. The clutch size is usually eight. The female lays two to ten eggs in a well-concealed nest lined with down and breast feathers. Incubation lasts about four weeks.

Location and environment

The former range of the Hawaiian duck included all of the main Hawaiian islands except the islands of Lānaʻi and Kaho'olawe. Hawaiian ducks were found on the hottest coasts with suitable ponds as well as in the mountains that were up to high.(Perkins 1903, cited in Banko 1987b). This includes low wetlands, river valleys, and streams in mountains. "Genetically-pure Koloa populations were believed to occur on the islands of Kaua'i. but there is now evidence of hybridization within pure populations." The Hawaiian duck was extirpated on all other islands, but was subsequently reestablished on Oʻahu, Hawaiʻi, and Maui through release of captive-reared birds. However, all the Hawaiian ducks in the reestablished populations have bred with feral mallard ducks and have produced hybrid offspring that are fully fertile; consequently, "pure" Hawaiian ducks are still only found on Kauaʻi. With an approximate population of 2,200 birds. The species was reintroduced to O'ahu between 1958 and 1982. In 1989, twelve of these captured birds were released on the island of Maui. The species was also reestablished on the island of Hawaiʻi between 1976 and 1982 (U.S. Fish and Wildlife Service 2005). Throughout the 1980s, the importation of mallards to Hawaiʻi was limited in an effort to reduce hybridization with Hawaiian ducks. Other conservation efforts for the Hawaiian duck include the development of "techniques for the identification of hybrids", "Determination of the population status of Hawaiian ducks and whether there are any pure Hawaiian ducks left on O`ahu will require simultaneous genetic testing and morphological characterization to develop reliable morphological criteria for distinguishing Hawaiian ducks, female mallards, and hybrids. Once such criteria are available they can be used to identify birds for removal in order to reduce interbreeding and introgression." The "conversion of flooded taro fields to dry sugar-cane acreage" destroys parts of this species' habitat. More information is still required for distinguishing hybrids (visually is too difficult, requires genetic screening), conserving habitat, examining migratory patterns and measuring the extent different wetlands affect the Hawaiian duck. It is an ongoing issue that requires constant attention, the more accurate the research is, the better of an idea we have of where money should be spent to help the Hawaiian duck survive. With that said, the Hawaiian Bird Conservation Action Plan has come up with a five-year plan to hopefully negate some of the species' main threats such as hybridization, habitat restoration/management and predator control. They want to "manage hybridization on all islands by removing feral Mallards and hybrids to the maximum extent practicable." Other conservation plans include plans to "obtain public acceptance of feral duck control", "continue protection and restoration of important wetland habitats", and "develop alternative predator control methods and explore the use of predator fences."*

References

  • Hawaii State Koloa Plan
  • Birding Hawaii: Koloa species profile