The Blue Duck ( Hymenolaimus malacorhynchus ) is a member of the duck, goose and swan family Anatidae. It is in the shelduck subfamily Tadorninae, and is the only member of the genus Hymenolaimus. The Maori name is Whio.

This 54 cm long species is an endemic resident breeder in New Zealand, nesting in hollow logs, small caves and other sheltered spots. It is a rare duck, holding territories on fast flowing mountain rivers.

It is a powerful swimmer even in white water, but is very reluctant to fly. It is difficult to find, but not particularly wary when located.

Blue Duck is a stocky dark grey duck with a paler bill and eye. The whitish bill has odd flaps of skin hanging from the sides of its tip. The male's call is a shrill whistle, and the female's is a low growl.

This is a very localised species now due to predation from introduced mammals, competition for its invertebrate food with introduced trout, and damming of mountain rivers for hydroelectric schemes.

Reference

• Wildfowl by Madge and Burn, ISBN 0-7470-2201-1