Bird facts: Blue duck

The extremely rare and endangered blue duck is one of New Zealand’s rarest birds, being confined to remote mountainous white-water streams in the west of South Island and central parts of North Island. Known as “Whio” after the whistling call of the male, the blue duck (Hymenolaimus malacorhynchos) is unique to New Zealand and has no close relatives, being the only species in its genus. It is a small bird around 53 cm (22 in) long.

The blue duck is unusual in that the male guards the ducklings, whereas in many duck species only the female raises the young. The blue duck is strongly territorial and a pair remain together for life. Their territory is quite large, being a length of around 1km of the stream.

While the blue duck has no close relatives it does share the characteristics of two other ducks in South America and New Guinea, since all three species live all year on fast-flowing streams, and these are the only species to do this. The blue duck’s habitat is now confined to remote, fast-flowing mountain streams. It dives into rapids, and is able to cling to submerged rocks and boulders in even the most swift-flowing water, which gives rise to another nickname: the torrent duck.

The blue duck is an unusual duck in that it mostly eats aquatic insects and their larvae, but it will also eat small crustaceans and algae. It has specialised projections on the tip of the bill to help them collect their food in fast flowing water.

The blue duck is active only at dawn and dusk. During the day it rests against the slate blue-grey rocks in its environment, its colouration acting as an effective camouflage against these rocks. It is entirely blue-grey apart from dark chestnut-coloured speckles on its breast. Its bill is pale pink, and the eyes are bright yellow.

Even though the blue duck is camouflaged and difficult to spot, its existence is threatened by illegal duck shooting, by predators such as the stoat and feral cat, and by its inability to fly well. Once so tame they could be caught by hand, blue ducks are now nervous and shy. The blue duck also has stiff competition for food from the introduced trout population. The greatest threat, however, is loss of habitat through deforestation and human encroachment.

The breeding season for the blue duck is between August and October (the New Zealand winter), with the female laying four to nine eggs in a nest in a cave or log jam, or hidden under thick flax bushes. Ducklings appear a month later, and they have unusually large webbed feet to help them cope with the swift-flowing waters. After eight to ten weeks the young are independent enough to seek out new territories for themselves, usually close to their parents’ territory.

Numbers of blue ducks are thought to be slowly declining as small, isolated populations become extinct. It is now extremely endangered.

References include:

Bird life International fact sheet: blue duck

New Zealand biodiversity website: http://www.biodiversity.govt.n z/land/nzbs/conservationland/s pecies/duck.html

New Zealand Department of Conservation fact sheet, available from: http://www.doc.govt.nz/templat es/page.aspx?id=33064

http://www.bdg.co.nz/blue_duck .0.html