Bird facts: Blue duck – Part 1

Of the World’s 162 waterfowl species, the rare and endangered blue duck (Hymenolaimus malacorhynchos) is perhaps the most unusual. It is one of only four species that live year round in riverine environments and unlike other duck species, it is an insectivore rather than an herbivore. It appears to be unrelated to any other duck species and has unique habits.

Living only in New Zealand, in remote regions of both the North and South Islands, it was given the name whio by the Maori because the call of the male bird has that sound. Many of the names Maori gave to native birds are based on the calls the birds make.

Besides blue duck and whio, it is also known as the mountain duck, torrent duck or whistling duck.

Description:

The blue duck is a comparatively small duck, up to 53 centimeters in length with the adult males weighing around 900 grams and the females 750 grams, approximately 70 percent of a mallard duck’s body mass. They are a slate colored blue-gray with dark chestnut spotted breasts, providing them with excellent camouflage amongst the rapids and riffles where they live and feed. Most ducks have an iridescent patch called the speculum in the center of each wing, but the blue duck does not.

Their bill is a pale flesh color and is tipped with a soft, semicircular, fleshy lip that enables them to scrape insect larvae of rocks without wear and tear. They have bright yellow eyes and relatively large webbed feet tipped with strong claws that allow them to move easily through rapids and grip rocks firmly while they feed.

Although the male bird makes a distinctive, high-pitched aspirate (breathy) “whio” call, the female in contrast utters a guttural, rattle-like call.

Ecology:

Blue ducks are insectivores, primarily eating the larval forms of various fly species, such as the caddis fly, mayfly and stonefly, many species of which are extant in New Zealand. Since such larvae are typically found in abundance only in rivers and streams with good water quality, the presence of blue duck is taken as an indicator for good water quality. These larvae primarily emerge from beneath rocks and out of crevices to feed in the dawn and dusk periods, as such blue ducks are also crepuscular by nature.

Where most male ducks leave after mating, the blue duck male stays with the female and helps in the rearing of the chicks. It is thought that they might mate for life like some swan species, but this is still undetermined. They nest between August