- Hymenolaimus malacorhynchos
Also known by it's Maori name: Whio
Identification
Size: 53cm (21in); weight: male 1,000g, female 750g.
Sexes are similar, female is smaller. Overall colour is blue-grey with reddish-chestnut spots on the breast. Eyes are yellow; bill pale pink, with the upper mandible having a thick semi-circular, fleshy 'lip' that overlaps the lower mandible, allowing it to scrape insect larvae off underwater rocks, without causing wear on the bill.
Distribution
A threatened endemic to New Zealand. It is classified as a "Nationally Endangered" species, with current populations at about 2,500 individuals and declining. Early causes for the decline, were habitat loss, especially forest clearance for agriculture. Unless the causes for the decline can be remedied, the species is on the track for extinction.
Taxonomy
The Blue Duck (Hymenolaimus malacorhynchus) is a member of the duck, goose and swan family Anatidae. It is the only member of the genus Hymenolaimus, placed in the shelduck subfamily Tadorninae [citation needed] after previously being considered part of the paraphyletic "perching duck" assemblage. The Māori name is whio, which is an onomatopoetic rendition of the males' call. It is a unusual waterfowl species, being the only member of it's genus, with no close relative anywhere in the world. It is believed to have appeared early in the evolutionary history of New Zealand, this isolation having resulted in some unique behavioural and anatomical features.
Voice
The male's call is an aspirated whistle, and the female's is a rattling growl.
Habitat
It is a rare duck, holding territories on clean, fast flowing, bouldery streams, in the forested upper catchment areas of New Zealand rivers.
Behaviour
It is a powerful swimmer even in white water, but is reluctant to fly. It is difficult to find, but not particularly wary when located. Blue Ducks develop strong pair bonds, and an individual pair will stay on the same stretch of river (approx. 1km long) for many years. They will aggressively defend their territory from other Blue Ducks, Paradise Ducks and even gulls or shags. The larger male can live for about 12 years, but the smaller female is shorter lived. Nesting is between August and October, with incubation of 4-9 eggs being done by the female (35 days), while the male stands guard. The down-lined nest of grass and twigs, is built in a scrape in caves, in log jams or under river-side vegetation and consequently often destroyed by spring floods. Breeding success is therefore very variable from year to year. They are usually active during the early morning and late evening, when they are seen standing on rocks, or with head and neck underwater while feeding. During the rest of the day they hide in caves, log-jams or suchlike and some populations have become almost nocturnal. The male's call is a high-pitched whistled whio whio, whereas the female makes a guttural rattle.
References
For more information, see the NZ Department of Conservation website: [1]
