Data Zone
Justification of Red List category
This species has a very small population size, estimated to number less than 1,000 mature individuals. It is therefore assessed as Vulnerable.
Population justification
Recent research on the population genetics and movement ecology of the species indicates that only individuals on Kaua'i and Ni'ihau can be considered pure (Wells et al. 2019, Malachowski 2020). Engilis and Pratt (1993) estimated the population to number approximately 2,000 birds on Kaua'i. However, based on bi-annual surveys on Kaua'i, the 5 year average (2012-2016) population size was estimated to be 947 birds in total (751-1,185) (Paxton et al. 2021), roughly equivalent to 600 mature individuals. Survey data are considered minimum counts due to variation in detectability and the fact that montane streams commonly used by the species were not included, and additionally, Ni'ihau was not included in this analysis due to being inconsistently surveyed. The total number of mature individuals is therefore precautionarily placed in the range 700-999.
Trend justification
This species was previously suspected to be in decline primarily owing to hybridisation with feral A. platyrhynchos, however there is little evidence of hybridisation during the past decade on Kaua'i and as such, the frequency of hybrids is not thought to be increasing (Wells et al. 2019). Bi-annual surveys on Kaua'i indicate that both short (2006–2016) and long (1986–2016) term trends were positive (Paxton et al. 2021), with the five-year average minimum population size increasing in the latest three generation period (16.9 years; Bird et al. 2020) from approximately 300 birds in 1995-1999 to 947 birds in 2012-2016, indicating an increase of over 200%. This is likely to be a result of wetland habitat management and restoration, as well as the lower prevalence of mongoose on the island (Paxton et al. 2021). Trends are unknown on Ni'ihau but there is movement between the two islands and globally the population is estimated to be increasing given evidence of positive trends on Kaua'i.
Anas wyvilliana was once an inhabitant of all the main Hawaiian Islands (U.S.A.) except Lana'i and Kaho'olawe (USFWS 2005), but is now restricted to Kaua'i and Ni'ihau (Wells et al. 2019, Malachowski 2020).
It inhabits wetlands, including coastal ponds, lakes, swamps, flooded grasslands, mountain streams, anthropogenic water-bodies and occasionally boggy forests (Todd 1996, T. C. Telfer in litt. 1999). Breeding occurs year-round, with the peak nesting season between September and May (Malachowski et al. 2019). It is an opportunistic feeder, taking invertebrates, seeds and plant matter (USFWS 2005).
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 (USFWS 2011). The indiscriminate hunting of migratory waterbirds in the late 1800s and early 1900s took a heavy toll on the species' population (USFWS 2011). Consequently, the species was extirpated from all Hawaiian islands except Kaua'i and Ni'ihau by 1962 (Swedberg 1967). Hybridisation with feral A. platyrhynchos, and therefore the danger of genetic introgression, has been a major threat to the species' recovery (USFWS 2011) such that despite subsequent translocations, only individuals on Kaua'i and Ni'ihau can be considered pure (Wells et al. 2019, Malachowski 2020). 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). Although Mallards are present on Kaua'i, there is little evidence of hybridisation within the past decade and conspecific mates remain abundant (Wells et al. 2019). As such, the number of hybrids is not thought to be increasing. The primary cause of adult mortality is thought to be avian botulism, which occurs year-round (Malachowski 2020). Introduced mammalian predators are an additional threat to the species, primarily cats and dogs but potentially rats also (Malachowski 2020). Avian predators such as Tyto alba and Asio flammeus may also pose a threat to the species (Malachowski 2020). Mongoose predation could be occurring at low levels given that sightings continue to be reported on Kaua'i, although they may not be well established (USFWS 2011). Additional threats include altered hydrology, such as flood control and channelisation, and non-native invasive plants which are causing ongoing habitat degradation (USFWS 2011, Malachowski 2020). Pigs, goats and other feral ungulates may degrade nesting habitat (USFWS 2011). 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). Sea level rise and increase groundwater salinity as a result of climate change may result in wetland habitat loss and degradation (USFWS 2011).
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 (USFWS 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 (USFWS 2005). However, recent research on the population genetics and movement ecology of the species indicates that only individuals on Kaua'i and Ni'ihau can now be considered pure owing to extensive hybridisation with A. platyrhynchos (Wells et al. 2019, Malachowski 2020). 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). Efforts are ongoing to develop a key to distinguish between hybrids and pure individuals (USFWS 2021). 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. Predator control and habitat restoration is ongoing on Kaua'i (VanderWerf 2012). There is some monitoring of wetland areas and removal of carcasses for botulism outbreaks (USFWS 2021).
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
Vine, J.
Contributors
Engilis Jr., A., Marshall, A., Pratt, H.D., Telfer, T., Uyehara, K. & VanderWerf, E.
Recommended citation
BirdLife International (2024) Species factsheet: Hawaiian Duck Anas wyvilliana. Downloaded from
https://datazone.birdlife.org/species/factsheet/hawaiian-duck-anas-wyvilliana on 22/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/12/2024.