The Hawaiian duck (Anas wyvilliana) or koloa is a species of bird in the family Anatidae that is endemic to the large islands of Hawaiʻi. Taxonomically, the koloa is closely allied with the mallard (A. platyrhynchos). It differs in that it is monomorphic (with similarly marked males and females) and non-migratory. As with many duck species in the genus Anas, Hawaiian duck and mallards can interbreed and produce viable offspring, and the koloa has previously been considered an island subspecies of the mallard (Anas platyrhynchos). However, all major authorities now consider this form to be a distinct species within the mallard complex. 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.
Physiology
Appearance Both male and female are mottled brown in color and resemble a female mallard. The males are usually bigger than the females. The speculum feathers of both sexes are green to blue, bordered on both sides by white. The tail is dark overall, unlike the black-and-white tail of a mallard. The feet and legs are orange to yellow-orange. The bill is olive green in the male and dull orange with dark markings in the female. The adult male has a darker head and neck. The female is generally lighter-colored than the male and has plain back feathers. A first-year male Hawaiian duck looks like an eclipse-plumaged male mallard. Seasonal plumage differences, individual variation, and variation between islands can make it difficult to differentiate between Hawaiian ducks, female mallards and hybrids of Hawaiian ducks and mallards. In addition, the extent of hybridization at a location can contribute to the difficulty of identification.
Body size The male Hawaiian duck has an average length of 48–50 cm (19–19.5 in) and the female has an average length of 40–43 cm (15.5–17 in). On average, the male weighs 604 grams (21.3 ounces) and the female weighs 460 grams (16 ounces). The Hawaiian duck is typically smaller than the mallard by 20 to 30 percent.
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.
Behavior The Hawaiian duck is a very wary bird, often found in pairs instead of large groups. The koloa is most prominently found residing in the tall, wetland grasses and streams near the Kohala volcano on the main island of Hawaiʻi. 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. The young can take to the water soon after hatching, but cannot fly until about nine weeks of age. Offspring become sexually mature enough to reproduce after a year. A potential conservation problem is hybridizing with the mallard. It is currently unknown whether the female Hawaiian duck attracts the male mallard or whether the color variation of the male mallard attracts the female. In any case, evolution has not moved fast enough for the species to reach reproductive isolation, since this interbreeding creates viable hybrids. This interbreeding is one of the main causes for the endangerment of the Hawaiian duck.
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 7,000 feet (2,130 m) 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. Ni'ihau, and highlands of Hawaiʻi with hybrid swarms on O'ahu and Maui, 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. This consists of 2,000 on Kaua`i and 200 on Hawaiʻi. However, these ducks are in decline due to hybridization. They are also vulnerable to predators because of the low location of their nests on the ground. This makes it easier for invasive predators such as cats, pigs, dogs, and mongooses to attack them. In addition to predators, Kauai has experienced a loss of lowland wetland habitat, in turn affecting the Hawaiian ducks.
Conservation status Wildlife refuges including Hanalei National Wildlife Refuge on Kaua'i are essential breeding areas for Hawaiian ducks. 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", which in turn will result in "simultaneous genetic testing and morphological characterisation".
Hybridization
… excerpt ends here. Continue reading the full article.
