The Blue Duck
The Blue Duck (Maori name: “Whio Whio”) is a river specialist which inhabits clean, fast flowing streams in the forested upper catchments of New Zealand rivers. They occur nowhere else in the world.
The best time to see blue duck is when they are most active at around dawn and dusk, which is probably related to the habits of the aquatic insects upon which they prey. The larvae spend most of their time beneath the rocks in streams, emerging onto the rock surface at dusk and so becoming more readily available to the ducks. The blue duck moves readily through the rapids, climbing over boulders with the aid of well–developed claws and dives without hesitation into the swiftest currents where it can cling to boulders while feeding under water. It is truly a torrent duck.
In almost all ducks the male deserts the female and takes no part in raising the brood and may mate with a different duck each year but the male blue duck helps guard the ducklings and probably keeps the same mate. Most ducks have an iridescent patch, the speculum, in the centre of each wing; the blue does not. Like many of New Zealand’s endemic birds, they are not good flyers. All these features suggest that the blue duck is a very ancient inhabitant of New Zealand.
It is hard to spot the Ducks when they are quiet and still resting during the day. Against the blue grey rock of their environment, they are perfectly camouflaged.. A hundred years ago, Buller said they were so tame that he could almost catch them by hand but now the latest monitoring report says that they are becoming shy and nervous.
The blue duck is variously called the mountain duck, torrent duck or whistling duck and is not only unique to New Zealand but also unique among other waterfowl. It appears unrelated to any duck elsewhere in the world and many of its habits are peculiar to the species.
The blue duck has probably always been an inhabitant of bush streams and formerly occurred over most of the country although not in large numbers. It has now retreated from the lowlands to the swifter flowing streams of the more mountainous and wilder areas of the country.
It is a relatively small duck, about seventy per cent of the weight of a mallard duck. Apart from the dark chestnut spots on the breast, the duck is entirely blue-grey. The bill is a soft pale flesh colour and tipped with a soft membranous flap. The eyes are bright yellow. The characteristic whistle is produced only by the male and this is best rendered by the Maori name Whio. Maori names for birds are characteristically onomatopoeic. The female gives a vibrating or clattering note.
The bird is strongly territorial with a pair remaining together throughout life and defending their same patch of stream against other ducks. Nesting occurs between August and November, usually under dense vegetation close to the stream bank. Incubation of the 4–7 eggs lasts for about a month. The young ducklings are basically black and white but the black down has a dark green sheen, making them very difficult to see against the glistening water surface. Ducklings have disproportionately big feet, enabling them to cope with the wild water of mountain streams.
Both parents guard the ducklings for 8-10 weeks when they begin a more independent life. Juveniles disperse up and down their natal river and attempt to settle and establish territories close to their natal territory, only occasionally shifting to other catchments. Most do not succeed in establishing territory and breeding until their second year.
Facts about blue duck/whio
Blue duck establish exclusive territories of up to a kilometre long. Strong pair bonding results in individual pairs occupying the same stretch of river year after year which they aggressively defend against other blue duck, as well as grey duck, paradise duck and even shags or gulls. The larger (1,000 gram) males can live for up to 12 years but smaller (750 gram) females are generally much shorter lived. Nesting and egg incubation of four to seven eggs is undertaken by the female while the male stands guard. Nests are shallow, twig, grass and down-lined scrapes in caves, under river-side vegetation or in log-jams, and are therefore very prone to spring floods. For this, and other reasons, their breeding success is extremely variable from one year to the next.
Blue duck require bouldery rivers and streams within forested catchments which provide high water quality, low sediment loadings, stable banks and abundant and diverse invertebrate communities. With such habitat requirements, blue duck are key indicators of river system health. The higher the number of breeding pairs of blue duck on a given stretch of river, the greater the life supporting capacity of that river.
The pre-European fossil record suggests that blue duck were once throughout New Zealand. They are currently considerably less widespread being limited to the less modified catchments of the Urewera, East Cape and central areas of North Island, and along the West Coast of South Island from Nelson to Fiordland.
There is growing concern for the species as most studies suggest that this already reduced range is continuing to contract. Remaining populations tend to be fragmented and isolated, have low reproductive success and are increasingly dominated by males. It is estimated that about 640 pairs remain on North Island while just under 700 pairs remain on South Island giving a total population of between 2,000 and 3,000 individuals.
This situation has resulted in a Department of Conservation species threat classification of “Nationally Endangered” – similar to kiwi and kokako. Blue duck are recorded by the International Union of Conservation for Nature (IUCN) as “Vulnerable”.