Justification of Red List Category
This species qualifies as Endangered because it is inferred to have a very small and fragmented range on a few islands, where wetlands are being lost and degraded, and where hybridisation is slowly reducing the number of pure individuals.
The species's population is estimated to number c.2,200 individuals (K. Uyehara, A. Marshall and A. Engilis Jr. in litt. 2007), roughly equivalent to 1,500 mature individuals.
The species is suspected to be in decline owing to hybridisation, wetland loss and introduced predators, although the likely rate of decline has not been estimated.
Anas wyvilliana was once an inhabitant of all the main Hawaiian Islands (U.S.A.) except Lana'i and Kaho'olawe (U.S. Fish and Wildlife Service 2005), but is now restricted to Kaua'i and Ni'ihau, and is reintroduced on O'ahu, Big Island and Maui. Its population was estimated to number 2,525 individuals (U.S. Fish and Wildlife Service 2002c), but this has been revised to 2,200 (K. Uyehara, A. Marshall and A. Engilis Jr. in litt. 2007), with c.2,000 on Kaua'i and Ni'ihau and c.200 on Big Island (Callaghan and Green 1993, Engilis and Pratt 1993, U.S. Fish and Wildlife Service 2005, K. Uyehara, A. Marshall and A. Engilis Jr. in litt. 2007). In 1997, 5-11 were seen on Maui (F. Duvall per P. Baker in litt. 1999). In addition, some of the c.300 birds on O'ahu and c.50 birds on Maui that resemble A. wyvilliana are pure birds (U.S. Fish and Wildlife Service 2005). However, most of the birds on these two islands are A. platyrhynchos × A. wyvilliana hybrids. The distribution and abundance of the species is not clear in some areas due to difficulties in the identification and distinguishing of hybrids (U.S. Fish and Wildlife Service 2005).
It inhabits wetlands, including coastal ponds, lakes, swamps, flooded grasslands, mountain streams, anthropogenic water-bodies and occasionally boggy forests, as high as 3,300 m (Todd 1996, T. C. Telfer in litt. 1999). Breeding occurs year-round, with the majority of breeding records coming between March and June (K. Uyehara, A. Marshall and A. Engilis Jr in litt. 2007). It is an opportunistic feeder, taking invertebrates, seeds and plant matter (U.S. Fish and Wildlife Service 2005). It favours larger (over 0.23 ha) wetlands far (at least 600 m) from human housing, and is twice as likely to be found on wetlands enhanced or created specifically for the species by the USDA's Wetlands Reserve Program than on agricultural ponds (Uyehara et al. 2008, K. Uyehara in litt. 2012).
A significant population decline in the early 20th century was brought about by nest predation by rats, mongooses, domestic dogs and cats, introduced fish and birds, habitat loss for agriculture and urban development, and local hunting pressure (U.S. Fish and Wildlife Service 2005). The indiscriminate hunting of migratory waterbirds in the late 1800s and early 1900s took a heavy toll on the species's population (U.S. Fish and Wildlife Service 2005). Presently, hybridisation with feral A. platyrhynchos, and therefore the danger of genetic introgression, is the primary threat to the species's recovery (U.S. Fish and Wildlife Service 2005). A. platyrhynchos was first imported to Hawaii in the late 1800s for ornamental ponds and farming, and in the 1950s and 1960s, hundreds were imported to stock hunting areas (Uyehara et al. 2007). On O'ahu, Maui and Big Island there are very few pure birds remaining (Engilis and Pratt 1993, Uyehara et al. 2007, Callaghan et al. in prep., K. Uyehara, A. Marshall and A. Engilis Jr in litt. 2007) with the probable exception (on the latter) of birds at high elevations on Kohala and Mauna Kea, where there are few feral A. platyrhynchos (Engilis and Pratt 1993, Uyehara et al. 2007, A. Engilis per H. D. Pratt in litt. 1999, K. Uyehara, A. Marshall and A. Engilis Jr in litt. 2007). Hybridisation appears to be beginning on Kaua'i, the species's largest population and so far largely free of hybrids (U.S. Fish and Wildlife Service 2005). Wetland loss and habitat modification by alien aquatic plants are also threats (M. Morin in litt. 1999). Pigs, goats and other feral ungulates may degrade nesting habitat (U.S. Fish and Wildlife Service 2005). On O'ahu at least, artificial wetlands associated with sugarcane plantations and aquaculture have disappeared as these industries have declined on the island (P. Donaldson in litt. 1999). Introduced predators (such as the small Asian mongoose Herpestes javanicus, rats, cats and dogs) are an additional factor (T. C. Telfer in litt. 1999). The species is also threatened by drought and human disturbance from recreation and tourism (K. Uyehara, A. Marshall and A. Engilis Jr in litt. 2007).
Conservation Actions Underway
On Kaua'i, the Hanalei National Wildlife Refuge is an important area for the species, especially in winter (Todd 1996). The species was reintroduced to O'ahu through the release of 326 captive-bred birds between 1958 and 1982 (U.S. Fish and Wildlife Service 2005); in 1989, fewer than 12 captive-bred birds were released on Maui; and between 1976 and 1982, the species was reestablished on the Big Island also through the release of captive-bred birds (U.S. Fish and Wildlife Service 2005). In the late 1980s, the importation of A. platyrhynchos was restricted by the state, with exceptions only for research and exhibition (Uyehara et al. 2007). In 2002, the department of agriculture placed an embargo on all birds shipped to the Hawaiian Islands, to protect the public from West Nile Virus. Research is being carried out to develop techniques for the identification of hybrids (Uyehara et al. 2007). This will require simultaneous genetic testing and morphological characterisation (U.S. Fish and Wildlife Service 2005).
44-51 cm. Small, deep-brown dabbling duck with orange legs. Males of two types both with greenish-olive bill with dark mark on culmen: brighter males with notable green speckling on crown and nape and reddish suffusion to the breast. Duller males more resemble female, which is mottled brown, redder on breast, and has a dark bill with variable tan or orange markings. Pale wing linings, emerald green to purplish-blue speculum. Similar spp. Mallard A. platyrhynchos female much larger, with white rather than buff outer tail feathers and blue-purple speculum. Hybrid A. platyrhynchos × A. wyvilliana can have any combination of parental characters, but usually larger than pure birds. Voice Quacking similar to that of A. platyrhynchos, but softer and uttered less often.
Text account compilers
Pilgrim, J., Sharpe, C J, Benstead, P., Khwaja, N., Taylor, J.
Telfer, T., Fretz, S., VanderWerf, E., Donaldson, P., Pratt, H., Engilis, Jr., A., Morin, M., Camp, R., Woodworth, B., Baker, H.C., Uyehara, K., Baker, P.E., Duvall, F., Gorresen, M., Marshall, A.
BirdLife International (2019) Species factsheet: Anas wyvilliana. Downloaded from http://www.birdlife.org on 22/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/09/2019.