Both parents guard the ducklings during their 70-80 days until fledging and the brood is raised entirely within the territory. The average clutch is 5 or 6 (range 3 – 8) and the incubation period extends for 33-35 days. The pale white eggs (each 60-65 g) are laid at 1.5-2 day intervals (e.g. While the female is incubating, the male waits on the riverside in close proximity to the nest. Nests are generally close to the river edge. Nests are generally well hidden from above and sites include riverside caves, holes in river banks, at bases of fern clumps or beneath fallen trees. Renesting is uncommon and rarely occurs later than November. Breeding is approximately 3-weeks later in much of the South Island. In the North Island, nesting begins in late August, with the first ducklings usually in late September. However, with blue ducks residing at low densities (an average of 1 pair per km of river), the scale at which this remedy has to be applied to protect remaining populations is daunting.īlue ducks are monogamous and fiercely territorial the territory and pair bond are maintained throughout the year. The effectiveness of small scale riparian predator trapping programmes points to a conservation remedy. The duck’s widespread declines throughout South Island beech ( Nothofagus) forests areas has highlighted the insidious effects of mast-seeding of beech trees fuelling a mouse population boom, closely followed by stoat increases and, when mice numbers crash, the predators focus on hole-nesting birds and vulnerable ground nesters like blue ducks. Nesting females are especially vulnerable to mammalian predators, particularly stoats and possums, while rats and weka have been implicated in nest and egg destructions. The breeding population is unlikely to be more than 1000 pairs (2011 estimate). There is a high prevalence of unpaired males on rivers without predator control. Principal physical correlates of habitat presently occupied include a stable river channel, coarse riverbed substrata, high water clarity, narrow stream/river widths, shallow river margins, pool and riffle sequences and forested river margins.Ī slow and insidious contraction of blue duck range continues, especially in remote South Island areas (parts of Fiordland, West Coast, and northwest Nelson) while some substantial population increases have occurred recently in selected areas where persistent and extensive riverside predator control is practised (western central North Island rivers, northern Te Urewera, Motueka region, Paparoa, Te Anau-Milford area). Here and there it extends downriver from these refugia into waters of modest gradient (50-80 m fall per km) provided riparian forest persists and the river runs clean. It is now patchily distributed in rivers in forested headwater catchments along the axial ranges of both islands. Its pre-human range extended from high altitude tarns, lakes and rivers to segments of bush-edged lowland rivers and lakes. The blue duck is endemic to New Zealand and present in the North and South Islands only. From a distance and in poor light, its size and shape may be confused with grey duck or mallard from which it can be readily distinguished by its uniform colouration and, if on the water, by its prominent tail tilted upwards and its head held erect. Similar species: the blue duck is unlike any other species when viewed in close proximity. The main female call is a low rasping growl given in response to disturbance or as a threat. Voice: male blue ducks give a high-pitched wheezy disyllabic whistle, “whi-o”, from which the Maori name ‘whio’ is derived.

Immatures are similar to the adults but from late summer to about August their eye is dark, their bill a dark grey and their chest spotting sparse and dark.

Males are larger than females, have more breast spotting and more prominent greenish iridescence on the head, neck and back. During aggressive interactions, or when birds are suddenly frightened, the bill epithelium is flushed with blood, and appears distinctly pink. Nowhere common, it lives at low densities and its shrill “whio” whistle above the noise of turbulent waters will usher in a long-remembered encounter.Īdults of both sexes are alike, being uniformly slate blue-grey with chestnut spotting on the breast, a pale grey bill with a conspicuously expanded black flap at its tip, dark grey legs and feet, and yellow eyes. The blue duck or whio is an iconic species of clear fast-flowing rivers, now mostly confined to high altitude segments of rivers in North and South Island mountain regions.

Mountain duck image dimensions