The blue duck (''Hymenolaimus malacorhynchos'') or whio is a member of the
duck
Duck is the common name for numerous species of waterfowl in the family (biology), family Anatidae. Ducks are generally smaller and shorter-necked than swans and goose, geese, which are members of the same family. Divided among several subfam ...
,
goose
A goose (: geese) is a bird of any of several waterfowl species in the family Anatidae. This group comprises the genera '' Anser'' (grey geese and white geese) and '' Branta'' (black geese). Some members of the Tadorninae subfamily (e.g., Egy ...
and
swan
Swans are birds of the genus ''Cygnus'' within the family Anatidae. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe (biology) ...
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Anatidae
The Anatidae are the biological family (biology), family of water birds that includes ducks, goose, geese, and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica. These birds are adapted f ...
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.
Taxonomy
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
Johann George Adam Forster, also known as Georg Forster (; 27 November 1754 – 10 January 1794), was a German geography, geographer, natural history, naturalist, ethnology, ethnologist, travel literature, travel writer, journalist and revol ...
mentioned the blue duck in their separate accounts of the voyage. 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". When in 1789 the German naturalist
Johann Friedrich Gmelin
Johann Friedrich Gmelin (8 August 1748 – 1 November 1804) was a German natural history, naturalist, chemist, botanist, entomologist, herpetologist, and malacologist.
Education
Johann Friedrich Gmelin was born as the eldest son of Philipp F ...
revised and expanded
Carl Linnaeus
Carl Linnaeus (23 May 1707 – 10 January 1778), also known after ennoblement in 1761 as Carl von Linné,#Blunt, Blunt (2004), p. 171. was a Swedish biologist and physician who formalised binomial nomenclature, the modern system of naming o ...
's ''
Systema Naturae
' (originally in Latin written ' with the Orthographic ligature, ligature æ) is one of the major works of the Sweden, Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Although the syste ...
'' he included the blue duck and placed it with all the other ducks in the
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
''
Anas''. He coined the
binomial name
In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...
''Anas malacorhynchos'' and cited the earlier works. The blue duck is now the only species placed in the genus ''Hymenolaimus'' that was introduced specifically for the species by
George Robert Gray
George Robert Gray (8 July 1808 – 6 May 1872) was an English zoology, zoologist and author, and head of the Ornithology, ornithological section of the British Museum, now the Natural History Museum, London, Natural History Museum, London f ...
in 1843.
The genus name combines the
Ancient Greek
Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), 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".
The species has no close relatives. Its taxonomic relationships with other waterfowl species remains uncertain; DNA analysis has placed it as a sister to the South American
dabbling duck
The Anatinae are a subfamily of the family Anatidae (swans, geese and ducks). Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving. The other members of the Anatinae are the extinct moa-nalo, a y ...
s (Anatini), but with no close relative. As of 2013, it was commonly listed as ''
incertae sedis
or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...
'' but likely within the
Anatinae
The Anatinae are a subfamily of the family Anatidae (swans, geese and ducks). Its surviving members are the dabbling ducks, which feed mainly at the surface rather than by diving. The other members of the Anatinae are the extinct moa-nalo, a ...
and allied to the
Anatini. It was formerly thought to be related to the
shelduck tribe.
It is commonly known in
New Zealand English
New Zealand English (NZE) is the variant of the English language spoken and written by most English-speaking New Zealanders. Its language code in ISO and Internet standards is en-NZ. It is the first language of the majority of the populati ...
by its
Māori name Whio, pronounced , which is an
onomatopoeic rendition of the males' call.
Other names it may be known by are Mountain Duck or Blue Mountain Duck.
Two
subspecies
In Taxonomy (biology), biological classification, subspecies (: subspecies) is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (Morphology (biology), morpholog ...
are recognised:
[
* ''H. m. hymenolaimus'' Mathews, 1937 – central, south North Island (New Zealand)
* ''H. m. malacorhynchos'' (Gmelin, JF, 1789) – west South Island (New Zealand)
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. However, the populations were defined as distinct subspecies by the International Ornithological Congress in 2022, based on strong genetic divergence and some plumage differences.][
]
Description
The blue duck is long and varies in weight by sex. Females are smaller than males, weighing , whereas the males weigh . The plumage is a dark slate-grey with a greenish sheen on the head, a chestnut-flecked breast. The outer 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. 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 .
Song
The male's call is a high-pitched whistle. The female's call is a rattling growl or low-pitched grating notes.
Behaviour
This species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
is an endemic
Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
resident breeder in New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
, 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.
Diet
The blue duck feeds almost entirely on aquatic invertebrate larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
e. A study of blue ducks on the Manganuiateao River in the central North Island found the most common prey items were Chironomidae
Chironomidae , commonly known as non-biting midges or chironomids , are a family of Nematoceran flies with a global distribution. They are closely related to the families Ceratopogonidae, Simuliidae, and Thaumaleidae. Although many chironomid ...
(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
Mayflies (also known as shadflies or fishflies in Canada and the upper Midwestern United States, as Canadian soldiers in the American Great Lakes region, and as up-winged flies in the United Kingdom) are aquatic insects belonging to the orde ...
, '' Aoteapysche'' (net-building caddis) and stonefly larvae. The blue duck on occasion take berries and the fruits of shrubs.[
]
Foraging
The foraging behaviour of the blue duck is characterised by its reliance on benthic invertebrates in fast-flowing riverine environments. Blue ducks primarily engage in dabbling behaviour where they feed by scouring rocks rather than up-ending or dabbling at the water's surface. Observations indicate that territorial males and females dabble approximately 96% of the time, with juvenile ducks dabbling 86% of the time. During the diurnal cycle, territorial birds exhibit higher foraging in the early morning and late evening, while non-territorial birds tend to forage more at midday. The decrease in dabbling during midday corresponds with an increase in diving behaviour in deeper pools. This pattern suggests that blue ducks capitalise on invertebrate resources that vary in availability throughout the day.[Eldridge, J. L. (1986). Territoriality in a river specialist: the blue duck. Wildfowl, 37(37), 123-135.] Diving behaviour was seen most frequent in March and July when water levels are higher and prey living on stones and boulders above the water-surface would have been inaccessible using alternative foraging methods. Blue ducks’ foraging activities peak during early morning and late afternoon, coinciding with the diurnal activity patterns of invertebrate drift. The reliance on these temporal patterns allows blue ducks to exploit a resource that is continuously recolonising denuded areas in the river.[Veltman, C. J., Triggs, S., Williams, M., Collier, K. J., McNab, B. K., Newton, L., ... & Henderson, I. M. (1991). The blue duck mating system: are river specialists any different? Acta XX Congressus Internationalis Ornithologici, 860-867.] Ducks can be seen feeding at other times but often the day and night is spent in hiding or resting.[Kear, J., & Burton, P. J. K. (1971). The food and feeding apparatus of the blue duck Hymenolaimus. Ibis, 113(4), 483-493.] Feeding behaviour is influenced by the type of prey available, requiring both tactile and visual foraging techniques. While foraging, blue ducks primarily glean invertebrates from rock surfaces using visual cues for mobile prey such as mayfly larvae. They have forward facing eyes that indicate this visual foraging use, typical of diving ducks, some attribute the evolution of this feature to the special absence of predators. Blue ducks also utilise tactile cues to scrape small chironomid larvae from submerged surfaces. [Martin, G. R., Jarrett, N., & Williams, M. (2007). Visual fields in Blue Ducks Hymenolaimus malacorhynchos and Pink‐eared Ducks Malacorhynchus membranaceus: visual and tactile foraging. Ibis, 149(1), 112-120.] Changes in water clarity can therefore significantly affect foraging efficiency, particularly for mobile prey. Territoriality in blue ducks is closely linked to the availability of food resources. Although blue ducks occupy large territories, the size is not primarily determined by food abundance; rather, it reflects the overlapping life cycles of benthic invertebrates, which exhibit minimal seasonal variation. This indicates that while food resources are critical for blue duck distribution and population structure, they do not necessarily dictate territorial size.[ Godfrey, J. D., Bryant, D. M., & Williams, M. (2003). Energetics of blue ducks in rivers of differing physical and biological characteristics. Science for Conservation, 214, 35-68.]
Territoriality
Blue ducks display territorial behaviours, they are known for their year-round territoriality, with territories typically ranging from 0.5 to 1.5 kilometres along river habitats characterised by alternating pools and rapids. The size and boundaries of these territories depend on resource availability, environmental conditions, and competition with other blue ducks. During the breeding season, territory defence becomes critical as breeding pairs protect their territories from intruders. This behaviour secures access to essential resources and optimal breeding sites, enhancing reproductive success.
Both male and female blue ducks cooperate to defend their territories, using a variety of behaviours to deter intruders. Defensive behaviours include head bobbing, vocalisations, and aggressive confrontations. These behaviours communicate their presence and resolve conflicts over territory.[Williams, M. (1991). Social and demographic characteristics of blue duck ''Hymenolaimus malacorhynchos''. Wildfowl, 42, 65-86.] The intensity of these interactions varies based on several factors, including the presence of a female during confrontations. When females are present, aggressive behaviours may escalate, highlighting the significance of mate guarding in territory defence. This interaction shows social and environmental factors shaping territorial behaviour. Territoriality in blue ducks is linked to habitat quality. Research indicates that pairs in higher-quality environments expend less energy on territorial defence, allowing for greater foraging opportunities and improved reproductive fitness. While pairs defend their territories, extensive areas between them may remain unprotected. Juvenile and unpaired blue ducks exploit these undefended spaces for foraging, indicating that territoriality does not completely limit resource availability for non-breeding individuals. After the breeding period, blue ducks may adjust their territorial size in response to resource availability, often reducing their territory to focus on the most productive areas. As the breeding season progresses, interactions between neighbouring pairs can intensify, particularly with increasing competition for shared resources. Most aggressive confrontations involve males defending territories against foraging intruders, highlighting male-male competition's role in shaping blue duck social dynamics.
Mating
Blue ducks exhibit a complex social structure characterised by strong pair bonds and monogamous behaviour, integral to their reproductive success and territory defence in riverine habitats. Typically, blue ducks maintain permanent year-round territories defended by mated pairs, emphasising the significance of monogamy for the successful rearing of offspring. [Veltman, C. J., Triggs, S., Williams, M., Collier, K. J., McNab, B. K., Newton, L., ... & Henderson, I. M. (1991). The blue duck mating system: are river specialists any different? Acta XX Congressus Internationalis Ornithologici, 860-867.] Pair members rarely stray far from each other, with individuals often remaining in close proximity throughout the year. In blue ducks, synchronous behaviours further enhance the stability of pair bonds, as pairs coordinate their activities, particularly during periods of brood dispersal and moulting. Pairs often forage together, displaying high synchronisation rates during various behavioural activities, which can range from 62% during moult to 81% in the pre-laying phase. This synchronised behaviour is said to likely improve foraging efficiency and reduces vulnerability to predation, reinforcing the significance of the social bonds. During incubation, males shift their foraging habits to support female partners and their offspring, highlighting a collaborative approach to parental care. Although blue ducks generally exhibit monogamous pair bonding, instances of extra-pair mating may occur, particularly when environmental pressures or territory dynamics shift.
Breeding
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.[
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.]
Captivity
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 programme 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 before dying out; efforts to create the only captive breeding
Captive breeding, also known as captive propagation, is the process of keeping plants or animals in controlled environments, such as wildlife reserves, zoos, Botanical garden, botanic gardens, and other Conservation biology, conservation facilitie ...
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. They have not been known to be exported and maintained anywhere else internationally.
Status
The blue duck is classified as Endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...
by the IUCN
The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
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.[
The blue duck is a very localised species now threatened by predation from introduced mammals such as stoats, competition for its ]invertebrate
Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...
food with introduced trout
Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...
, 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. 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. Female whio are especially vulnerable to stoats while nesting, and some populations are now 70 percent male. 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.
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.
References
Further reading
*
*
*
External links
*ARKive
Images and movies of the Blue Duck (''Hymenolaimus malacorhynchos'')
* ttps://web.archive.org/web/20130428083454/http://www.doc.govt.nz/conservation/native-animals/birds/wetland-birds/blue-duck-whio/ Blue duck/Whioat the Department of Conservation
TerraNature , New Zealand ecology – Blue duck (Whio)
Blue Duck Project Charitable Trust
Whio Forever Project
Central North Island Blue Duck Trust
{{Taxonbar, from=Q420499
Ducks
Tadorninae
Endemic birds of New Zealand
Birds described in 1789
Taxa named by Johann Friedrich Gmelin