Blue duck

The blue duck (Hymenolaimus malacorhynchos) or whio is a member of the duck, goose and swan family, Anatidae and is endemic to New Zealand. It is the only individual species belonging to the genus Hymenolaimus. Its closest relatives are the ducks in the genus Sarkidiornis.

First seen and recorded by the British explorer, James Cook in his second voyage to New Zealand, its scientific name was given by the German naturalist, Johann Friedrich Gmelin in 1789 and later George Robert Gray in 1843. There are two subspecies of the blue duck, one in North Island and the other in South Island. Common to both gender, its physical characteristics include yellow iris, a pale grey beak with semicircular flaps and lamellae, dark-slate grey plumage, chestnut flecked breast, dark grey webbed feet, and well developed claws. The male blue duck has a high-pitched whistle, which gave its Māori name Whio, while the female has a low-pitched rattle.

The European voyages led to more human settlement in New Zealand, causing a loss of forests, and which started the decline of Blue duck in the country. It was last commonly seen in New Zealand in the 1950s following which stoat predation caused its further population decline and limiting it to only North and South Island. Geographically, it is found in clean and stable rivers which have a medium to steep gradient. It roosts close to the undercut of river banks, and can do breeding and moulting in more wider area having tributaries and small streams.

Blue ducks have a territorial behaviour with paired ducks staying in its territory during and post-breeding season. Single males often attempt to intrude into paired blue duck territory with differing results while the juvenile ducks stay close to their catchment. It mostly feeds on aquatic invertebrate larvae such as Chironomidae and caddisfly larvae. Foraging is done by using both methods–dabbling and diving. Dabbling is more commonly used by the adult blue duck than the juvenile blue duck. Also, territorial blue duck forages on mornings and evenings, while non-territorial duck forages on midday. Paired ducks defend themselves using techniques for e.g., head-low flight, upright, head-bobbing, siphon-feeding and vocalisations. When ducklings learn to fly, they lose contact with their parent blue ducks which by then becomes flightless. In the breeding season, a clutch of 6 eggs are laid with an incubation period of 35 days. They build their nest between August and December, and during breeding season the male blue duck guards the territory while the female duck incubates the eggs.

The progeny of North Island blue duck subspecies are held and bred on both North and South Island, but are later returned to their respective island. In contrast, the South Island subspecies are held and bred only locally. The WHIONE programme, operating between 2009 and 2019, located the nest of these ducks for raising it in captivity. International efforts to raise the blue duck outside New Zealand was made in the United Kingdom in 1970s, but it lasted only until 2012. Its threats include weka, stoat, man-made actions and environmental hazards. The Central North Island Blue Duck Trust (CNIBDT) works in the conservation effort towards blue duck with projects such as the "Whio Forever Project". Predator control is done with aerial 1080 operations, which are run by TBfree New Zealand and the New Zealand Department of Conservation. The blue duck is depicted on the reverse side of the New Zealand $10 banknote.

From the Wikipedia article “Blue duck” (en.wikipedia.org/w/index.php?title=Blue_duck&oldid=1378444245), by Wikipedia contributors, licensed under CC BY-SA 4.0 (creativecommons.org/licenses/by-sa/4.0). This block is kept separate from our own text.