Of our eight native species of waterfowl, the most peculiar is undoubtedly the blue duck, mountain duck, or whio. Not only are its calls strange—the male has a shrill hoarse whistle and the female a rattling cry—but its relationship to all other waterfowl is extremely uncertain. Its nearest relative may be Salvadori's duck of New Guinea, but this is by no means beyond doubt and indeed, is denied by some.
With the exception of that of the now very probably extinct Auckland Island merganser, its recent geographical range is more limited than that of any other species of New Zealand waterfowl, for it has not been reliably reported beyond the North and South Islands. Within this range it is unknown north of Coromandel and is almost wholly restricted to swift mountain streams of our more extensive and isolated forest areas. Before settlement was advanced its range was rather wider in both islands, but forest destruction and stream aggradation have spoiled a great deal of what was once good habitat.
Many a stretch of bush- or tussock-fringed mountain stream, however, supports a pair of these confiding and sombre-plumaged birds swimming powerfully against the current, bobbing down through a rapid, or basking drowsily on a current-washed rock. Their colour is a slate or lead blue, with chestnut mottling on the breast and abdomen. The pinkish down-turned bill is black at its tip, legs are dark brown, eyes yellow, and the tail is characteristically long. Both sexes are very similar in appearance. Although they are accomplished swimmers and divers, blue ducks also fly well, but rather seldom and then mainly at early morning or dusk. They feed on aquatic insects and their larvae. Breeding occurs from August to November, and about six narrow cream-coloured eggs are laid in holes in banks, logs, or under thick vegetation at the stream's edge.
The scientific name of the species is Hymenolaimus malacorhynchos.
by Gordon Roy Williams, B.SC.(HONS.)(SYDNEY), Lecturer in Agricultural Zoology, Lincoln Agricultural College.