Hymenolaimus malacorhynchos
blue duck

Blue ducks (also called whistling ducks or whios) are only found in New Zealand. They were once widespread throughout the North and South Islands and appears to have occupied more diverse habitats than today (Worthy & Holdaway, 1994). Blue ducks are now restricted to upland forested catchments in eastern and central North Island and the west coast of South Island. There are no fossil records from the Chatham Islands, Stewart or Great Barrier Islands, or other, smaller islands. Although the initial impact of human settlement and the arrival of terrestrial mammals on blue ducks remains speculative, a significant decline in the number of blue ducks has occurred in the past 150 years. Remaining populations have suffered from fragmentation and habitat degradation and remain in isolated areas where rivers are not as disturbed. One of the largest North Island populations is found on Manganuiateao River. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; Worthy and Holdaway, 1994)

Blue ducks spends their entire life on rivers or streams generally in mountainous regions. Although they are likely to be restricted to these more marginal habitats because of the destruction and fragmentation of intact riverine habitats elsewhere. Their habitat has been affected negatively by riverside and agricultural development. River sections in which blue ducks are found today are generally free from sediment, have native scrub and woodland vegetation along their banks, and have a wide variety and abundance of aquatic invertebrates. They prefer stream and river banks with steep slopes, dense vegetation, and overhanging branches over the river. (Collier and Lyon, 1991)

Blue ducks are relatively small ducks. As their name suggests, blue ducks have dusky blue-grey plumage with chestnut markings on the chest. Their coloration makes them camouflaged on the blue-gray rocks of their native New Zealand river banks. Adult blue duck bills are light pink and the eyes are yellow. Juveniles have a grey bill and gray eyes. They are about 53 cm long and males are slightly larger than females, averaging 1000 g to the average female weight of 800 g. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

The blue duck mating system is unlike that of many other ducks in that both males and females stay and help raise the brood each year. This is unlike most ducks, where the male will usually leave the female to incubate and raise the young. It is also believed that blue ducks remain paired for life and defend the same territory in their August through November nesting period. Pairs defend small territories of 0.7 to 1 km along a river. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

Most males will not breed until their second year while most females mate at one year old and produce one clutch a year. Females can produce anywhere from 4 to 7 white eggs each year. Each egg weighs about 10% of female body weight or about 70 g. Females commonly make their nests in dense vegetation along streambanks; usually in small riverside caves or under the cover of flax and grass. While the female incubates for about a month, the male is usually in close proximity to help protect the nest site. Ducklings hatch with disproportionately large feet, which helps them battle swift currents to feed themselves. Hatchlings are primarily black and white with a dark green sheen, which makes them difficult to see against the surface of the water. Both males and females continue to guard the young for 8 to 10 weeks after hatching or until they disperse. Blue duck juveniles are reluctant to disperse from their birth territory. Other aspects of their breeding behavior are not reported in the literature. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

Male and female blue ducks care for and protect their young. Females incubate the eggs while males protect the nesting territory. Both parents help to protect and feed their hatchlings. ("Hymenolaimus malacorhynchos", 2008)

Most blue ducks live to about 8 years, although living to 10 years is not uncommon. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997)

Blue ducks are most active at dawn and dusk. Populations do not migrate, with territorial mated pairs defending small sections of river during the breeding season. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

Mated pairs defend small territories of 0.7 to 1 km along a river.

Females give a drawn out “craak.” Males give a husky whistle, from which the name “whio” comes. This is also why these ducks are referred to as whistling ducks. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

Blue ducks feed entirely on freshwater invertebrates, mostly caddisfly larvae (Trichoptera), but also stonefly (Plecoptera) and mayfly (Ephemeroptera) nymphs, snails (Gastropoda), and midges (Chironomidae). Some South Island birds were found eating fruits of streamside plants. Their preference for invertebrates puts them in direct competition with trout species that have been introduced into New Zealand streams and are one of the many factors contributing to their endangered status. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997)

Blue ducks are heavily preyed on by introduced mammals, which have contributed significantly to population declines. Introduced predators include rats (Rattus), feral cats (Felis catus), feral dogs (Canis lupus familiaris), stoats (Mustela erminea), ferrets (Mustela putorius), and least weasels (Mustela nivalis). Native predators of eggs include brush-tailed possums (Trichosurus vulpecula) and wekas (Gallirallus australis). Hatchlings can also be taken by gulls (Larus), hawks (Accipitridae), eels (Anguillidae), shags (Phalacrocorax), and falcons (Falco), which also take adults. Blue ducks tend to be camouflaged in their stream and streamside habitats. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)

Blue ducks are important predators of aquatic insects in their native, riverine habitats. ("Hymenolaimus malacorhynchos", 2008)

Blue ducks are attractive and interesting members of native New Zealand ecosystems, attracting birdwatchers and other wildlife enthusiasts.

There are no known adverse effects of blue ducks on humans.

Blue duck populations have experienced significant populations declines are most directly impacted by four threats; habitat loss and disturbance, competition with non-native trout (Salmonidae), predation, especially by non-native mammals, and population fragmentation. Hydroelectric dams and human recreational activity on rivers also disturbs blue duck populations. The diversity of threats affecting blue duck populations makes it imperative that conservation efforts are employed. In 1988 the Blue Duck Conservation Strategy was put into effect and was active until 1992. This conservation effort resulted in increased knowledge was obtained about blue duck distribution, demography, ecology and population on various rivers. Knowledge about the techniques used for re-establishment was increased through translocation efforts and public awareness was increased. Since then, The Department of Conservation Blue Duck Recovery Plan was approved in 1997 and is currently active. This plan also has the long term goal of maintaining blue duck populations in the wild in secure river catchments. Populations are estimated at about 1200 individuals and sex ratios are skewed towards males. South Island populations are most threatened. Captive breeding and reintroduction efforts are underway, with the goal of creating 5 viable populations in areas where non-native predators are being controlled. ("Blue Duck (Whio), Hymenolaimus malacorhynchos Recovery Plan", 1997; "Hymenolaimus malacorhynchos", 2008)