Blue ducks are heavily preyed on by introduced mammals, which have contributed significantly to population declines. Introduced predators include rats (Rattus), feral cats (Felis catus), feral dogs (Canis lupus familiaris), stoats (Mustela erminea), ferrets (Mustela putorius), and least weasels (Mustela nivalis). Native predators of eggs include brush-tailed possums (Trichosurus vulpecula) and wekas (Gallirallus australis). Hatchlings can also be taken by gulls (Larus), hawks (Accipitridae), eels (Anguillidae), shags (Phalacrocorax), and falcons (Falco), which also take adults. Blue ducks tend to be camouflaged in their stream and streamside habitats.
Known Predators:
Anti-predator Adaptations: cryptic
Blue ducks are relatively small ducks. As their name suggests, blue ducks have dusky blue-grey plumage with chestnut markings on the chest. Their coloration makes them camouflaged on the blue-gray rocks of their native New Zealand river banks. Adult blue duck bills are light pink and the eyes are yellow. Juveniles have a grey bill and gray eyes. They are about 53 cm long and males are slightly larger than females, averaging 1000 g to the average female weight of 800 g.
Average mass: 800-1000 g.
Average length: 53 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Most blue ducks live to about 8 years, although living to 10 years is not uncommon.
Range lifespan
Status: wild: 10 (high) years.
Average lifespan
Status: wild: 8 years.
Blue ducks spends their entire life on rivers or streams generally in mountainous regions. Although they are likely to be restricted to these more marginal habitats because of the destruction and fragmentation of intact riverine habitats elsewhere. Their habitat has been affected negatively by riverside and agricultural development. River sections in which blue ducks are found today are generally free from sediment, have native scrub and woodland vegetation along their banks, and have a wide variety and abundance of aquatic invertebrates. They prefer stream and river banks with steep slopes, dense vegetation, and overhanging branches over the river.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: rivers and streams
Other Habitat Features: riparian
Females give a drawn out “craak.” Males give a husky whistle, from which the name “whio” comes. This is also why these ducks are referred to as whistling ducks.
Communication Channels: acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Blue duck populations have experienced significant populations declines are most directly impacted by four threats; habitat loss and disturbance, competition with non-native trout (Salmonidae), predation, especially by non-native mammals, and population fragmentation. Hydroelectric dams and human recreational activity on rivers also disturbs blue duck populations. The diversity of threats affecting blue duck populations makes it imperative that conservation efforts are employed. In 1988 the Blue Duck Conservation Strategy was put into effect and was active until 1992. This conservation effort resulted in increased knowledge was obtained about blue duck distribution, demography, ecology and population on various rivers. Knowledge about the techniques used for re-establishment was increased through translocation efforts and public awareness was increased. Since then, The Department of Conservation Blue Duck Recovery Plan was approved in 1997 and is currently active. This plan also has the long term goal of maintaining blue duck populations in the wild in secure river catchments. Populations are estimated at about 1200 individuals and sex ratios are skewed towards males. South Island populations are most threatened. Captive breeding and reintroduction efforts are underway, with the goal of creating 5 viable populations in areas where non-native predators are being controlled.
US Migratory Bird Act: no special status
US Federal List: no special status
CITES: no special status
IUCN Red List of Threatened Species: endangered
There are no known adverse effects of blue ducks on humans.
Blue ducks are attractive and interesting members of native New Zealand ecosystems, attracting birdwatchers and other wildlife enthusiasts.
Blue ducks are important predators of aquatic insects in their native, riverine habitats.
Blue ducks feed entirely on freshwater invertebrates, mostly caddisfly larvae (Trichoptera), but also stonefly (Plecoptera) and mayfly (Ephemeroptera) nymphs, snails (Gastropoda), and midges (Chironomidae). Some South Island birds were found eating fruits of streamside plants. Their preference for invertebrates puts them in direct competition with trout species that have been introduced into New Zealand streams and are one of the many factors contributing to their endangered status.
Animal Foods: insects; mollusks
Plant Foods: fruit
Primary Diet: carnivore (Insectivore )
Blue ducks (also called whistling ducks or whios) are only found in New Zealand. They were once widespread throughout the North and South Islands and appears to have occupied more diverse habitats than today (Worthy & Holdaway, 1994). Blue ducks are now restricted to upland forested catchments in eastern and central North Island and the west coast of South Island. There are no fossil records from the Chatham Islands, Stewart or Great Barrier Islands, or other, smaller islands. Although the initial impact of human settlement and the arrival of terrestrial mammals on blue ducks remains speculative, a significant decline in the number of blue ducks has occurred in the past 150 years. Remaining populations have suffered from fragmentation and habitat degradation and remain in isolated areas where rivers are not as disturbed. One of the largest North Island populations is found on Manganuiateao River.
Biogeographic Regions: australian (Native )
Other Geographic Terms: island endemic
The blue duck mating system is unlike that of many other ducks in that both males and females stay and help raise the brood each year. This is unlike most ducks, where the male will usually leave the female to incubate and raise the young. It is also believed that blue ducks remain paired for life and defend the same territory in their August through November nesting period. Pairs defend small territories of 0.7 to 1 km along a river.
Mating System: monogamous
Most males will not breed until their second year while most females mate at one year old and produce one clutch a year. Females can produce anywhere from 4 to 7 white eggs each year. Each egg weighs about 10% of female body weight or about 70 g. Females commonly make their nests in dense vegetation along streambanks; usually in small riverside caves or under the cover of flax and grass. While the female incubates for about a month, the male is usually in close proximity to help protect the nest site. Ducklings hatch with disproportionately large feet, which helps them battle swift currents to feed themselves. Hatchlings are primarily black and white with a dark green sheen, which makes them difficult to see against the surface of the water. Both males and females continue to guard the young for 8 to 10 weeks after hatching or until they disperse. Blue duck juveniles are reluctant to disperse from their birth territory. Other aspects of their breeding behavior are not reported in the literature.
Breeding interval: Blue ducks breed once a year.
Range eggs per season: 4 to 7.
Average age at sexual or reproductive maturity (female): 1 years.
Average age at sexual or reproductive maturity (male): 2 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Male and female blue ducks care for and protect their young. Females incubate the eggs while males protect the nesting territory. Both parents help to protect and feed their hatchlings.
Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female)
The blue duck or whio (Hymenolaimus malacorhynchos) is a member of the duck, goose and swan family Anatidae endemic to New Zealand. It is the only member of the genus Hymenolaimus. Its exact taxonomic status is still unresolved, but it appears to be most closely related to the tribe Anatini, the dabbling ducks.
The whio is depicted on the reverse side of the New Zealand $10 banknote.
Captain James Cook saw the blue duck in Dusky Sound, South Island, New Zealand, on his second voyage to the south Pacific. In 1777 both Cook and the naturalist Georg Forster mentioned the blue duck in their separate accounts of the voyage.[2][3] A specimen was described in 1785 by the English ornithologist John Latham in his A General Synopsis of Birds. Latham used the English name, the "soft-billed duck".[4] When in 1789 the German naturalist Johann Friedrich Gmelin revised and expanded Carl Linnaeus's Systema Naturae he included the blue duck and placed it with all the other ducks in the genus Anas. He coined the binomial name Anas malacorhynchos and cited the earlier works.[5] The blue duck is now the only species placed in the genus Hymenolaimus that was introduced specifically for the species by George Robert Gray in 1843.[6][7] The genus name combines the Ancient Greek humēn, humenos meaning "skin" or "membrane" with laimos meaning "throat". The specific epithet malacorhynchos is also from Ancient Greek and combines malakos meaning "soft" with rhunkhos meaning "bill".[8]
The species has no close relatives.[9] Its taxonomic relationships with other waterfowl species remains uncertain; DNA analysis has placed it as a sister to the South American dabbling ducks (Anatini), but with no close relative. As of 2013, it was commonly listed as incertae sedis but likely within the Anatinae and allied to the Anatini.[10] It was formerly thought to be related to the shelduck tribe.[11][12]
It is commonly known in New Zealand English by its Māori name Whio, pronounced /ˈfiɔː/ FEE-oh, which is an onomatopoeic rendition of the males' call.[13][14] Other names may be known by are Mountain Duck or Blue Mountain Duck.[14]
Two subspecies are recognised:[7]
Prior to 2022, the North Island and South Island whio were considered distinct but were not distinguished as subspecies; they were, however, treated as separate management units.[15] However, the populations were defined as distinct subspecies by the International Ornithological Congress in 2022, based on strong genetic divergence and some plumage differences.[7]
The blue duck is 53 cm (21 in) long and varies in weight by sex. Females are smaller than males, weighing 680–870 g (24–31 oz), whereas the males weigh 820–970 grams (29–34 oz).[16] The plumage is a dark slate-grey with a greenish sheen on the head, a chestnut-flecked breast. The outer secondaries are tipped with white and the inner ones have black margins. The plumage of the two sexes are mostly the same, although the female has slightly less chestnut in the chest.[17] The pinkish-white bill has fleshy flaps of skin hanging from the sides of its tip. The beak is green at hatching and develops its final colour eight hours later .
The male's call is a high-pitched whistle.[13][14] The female's call is a rattling growl or low-pitched grating notes.[13][14][18]
This species is an endemic resident breeder in New Zealand, nesting in hollow logs, small caves and other sheltered spots. It is a rare duck, holding territories on fast flowing mountain rivers. It is a powerful swimmer even in strong currents, but is reluctant to fly. It is difficult to find, but not particularly wary when located.
The blue duck feeds almost entirely on aquatic invertebrate larvae. A study of blue ducks on the Manganuiateao River in the central North Island found the most common prey items were Chironomidae (midge) and cased caddisfly larvae, although cased caddisfly were less preferred and were only consumed so much because of their abundance. Hydrobiosidae (free-living caddisfly) and Aphrophila neozelandica (crane fly) larvae were also frequently eaten. Other prey included mayfly, Aoteapysche (net-building caddis) and stonefly larvae.[19] The blue duck on occasion take berries and the fruits of shrubs.[1]
Blue ducks nest between August and October, laying 4–9 creamy white eggs. The female incubates the eggs for 31 to 32 days and chicks can fly when about 70 days old.[16]
Nesting and egg incubation of four to seven eggs is undertaken by the female while the male stands guard. Nests are shallow, twig, grass and down-lined scrapes in caves, under river-side vegetation or in log-jams, and are therefore very prone to spring floods. For this, and other reasons, their breeding success is extremely variable from one year to the next.[20]
Captive North Island whio are held and bred on both main islands of New Zealand, but the progeny are returned to their respective island. South Island whio are held and bred in captivity on the South Island only. All captives are kept by approved and permitted zoological and wildlife facilities as part of the national recovery plan. As part of this current ten-year plan (2009–2019) is the WHIONE program which works with specially trained nose dogs to locate nests. The eggs are removed, and the ducklings hatched and raised in captivity. Later they are conditioned for coordinated release.
Blue ducks were presented to the International Waterfowl Association in the UK in the 1970s along with New Zealand shovelers, New Zealand scaup, and brown teal by The Wildlife Service of New Zealand. The species was maintained in the UK until at least 2012[21] before dying out; efforts to create the only captive breeding population outside of New Zealand with these ducks ultimately failed when the last two male ducks formed a same-sex relationship with each other instead of with the female that was assigned to them.[22] They have not been known to be exported and maintained anywhere else internationally.[23]
The blue duck is classified as Endangered by the IUCN due to its highly fragmented and shrinking population, and it is listed as Nationally Endangered in the New Zealand Threat Classification System. A 2010 census estimated a total population size of 2,500–3,000 individuals, with a maximum of 1,200 pairs.[1]
The blue duck is a very localised species now threatened by predation from introduced mammals such as stoats, competition for its invertebrate food with introduced trout, and damming of mountain rivers for hydroelectric schemes. Early recovery efforts by scientists, field workers and volunteers have been summarised in a project sponsored by Genesis Energy, the Central North Island Blue Duck Charitable Conservation Trust and the Royal Forest and Bird Protection Society in 2006.[24] In 2009 the New Zealand Department of Conservation started a ten-year recovery programme to protect the species at eight sites using predator control and then re-establish populations throughout their entire former range.[25] Female whio are especially vulnerable to stoats while nesting, and some populations are now 70 percent male.[26] In one study area, clutches of eggs lasted an average of nine days before being destroyed by stoats, and the one brood that hatched was killed the next day.[26]
In 2011 the New Zealand Department of Conservation and Genesis Energy started the Whio Forever Project, a five-year management programme for whio. It will enable the implementation of a national recovery plan that will double the number of fully operational secure blue duck breeding sites throughout New Zealand, and boost pest control efforts.
The blue duck or whio (Hymenolaimus malacorhynchos) is a member of the duck, goose and swan family Anatidae endemic to New Zealand. It is the only member of the genus Hymenolaimus. Its exact taxonomic status is still unresolved, but it appears to be most closely related to the tribe Anatini, the dabbling ducks.
The whio is depicted on the reverse side of the New Zealand $10 banknote.
