Blue duck
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.
It is commonly known in New Zealand English by its Māori name Whio, pronounced "fee-o" (o as in sock) which is an onomatopoeic rendition of the males' call.[2][3] Other names may be known by are Mountain Duck or Blue Mountain Duck.[3]
The blue duck is 53 to 54 cm (21–21 in) long and varies in weight by sex. Females are smaller than males, weighing 680–870 g (24–31 oz), whereas the males weigh 820–1,077 g (28.9–38.0 oz). 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.[4] The pinkish-white bill has fleshy flaps of skin hanging from the sides of its tip. The blue duck hatches with a green beak for just 8 hours after hatching; after which it then develops its final colour.
The male's call is a high-pitched whistle.[2][3] The female's call is a rattling growl or low-pitched grating notes.[2][3][5]
The blue duck was first described in the 13th edition of the Systema Naturae published by Johann Friedrich Gmelin in 1789. The species is the only member of its genus and has no close relatives.[6] 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.[7] It was formerly thought to be related to the shelduck tribe.[8][9]
Although the North Island and South Island whio are genetically distinct, they are not described as subspecies; they are, however, treated as separate management units.[10]
