Duck (Blue) Hymenolaimus malacorhynchos
Species: H. malacorhynchos
Binomial name: Hymenolaimus malacorhynchos
Common names: Blue duck, Their Maori name is whio in the North Island or ko whio whio in the South Island.
Hymenolaimus malacorhynchos is a protected endemic species of duck found nowhere else in the world. They are classified as nationally endangered, and the total population was estimated at 2,500 in 2004. Their habitat is New Zealand’s North and South Island steep mountain streams and forested rivers which are far too swift and rough for most ducks. It has specialised features that are well adapted to this habitat. It has developed has large, webbed feet to give it power in fast-flowing water, and large claws for rough terrain. Even hatchlings have oversize feet and strong legs, ready to swim in swift currents and jump onto large rocks and logs.
A male defends it territory with a high whistle that carries beyond noisy rapids – hence its Maori name, which means whistle. The female has a grating alarm call.
Hymenolaimus malacorhynchos are about 53 centimetres long. The males weigh 900 grams and females 750 grams. They are a blue-grey colour with a flecked chestnut breast. This colouration helps it to blend in with its environment.
They mainly feed at dawn and dusk on insect larvae – including caddisfly, mayfly and stonefly larvae – which it scrapes off rocks underwater. Its bony bill is protected from abrasion by a fleshy flap.
They are now nationally vulnerable and their decline has occurred to the loss of the lowland forests. They are flightless during the moult period which makes them extremely vulnerable to predation from stoats, cats, ferrets, and dogs. The introduction of trout has had an effect as they compete for the same food.
Research in Te Urewera demonstrated that 90% of the nests failed in an area without predator control. It was also demonstrated that 46% of the females were killed during the moult period when they retreated up small side stream to avoid disturbance.
Listen to the call of Blue duck.
They feature on our $10 note.
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