Blue Duck (Hymenolaimus malacorhynchos)

Blue Duck

[order] ANSERIFORMES | [family] Anatidae | [latin] Hymenolaimus malacorhynchos | [authority] Gmelin, 1789 | [UK] Blue Duck | [FR] Canard bleu | [DE] Saumschnabel-Ente | [ES] Pato Azul | [NL] Blauwe Eend.

Subspecies

Monotypic species

Genus

The Blue Duck (Hymenolaimus malacorhynchos) is one of New Zealand’s ancient endemic species. It is the only member of its genus and its taxonomic relationships with other waterfowl are uncertain. It lives year-round on rivers, a mode of life it shares with only three of the world’s other 169 waterfowl species. In pre-human times, blue ducks were widely distributed throughout both main islands of New Zealand at which time they appear to have occupied more diverse habitats than those of today. Although the initial impact of human settlement and the arrival of ground-dwelling mammals on blue ducks will remain conjectural, a significant reduction in blue duck numbers and range has occurred over the past 150 years. In early times blue ducks were widespread throughout both main islands of New Zealand, except in Northland, and possibly coastal parts of Canterbury and Otago. There are no fossil records from the Chatham Islands, Stewart or Great Barrier Islands, or other smaller islands. Early naturalists refer to the duck’s presence in alpine rivers and tarns, as well as some lowland rivers.

Physical charateristics

The Blue Duck is a dark slate-grey with a chestnut-flecked breast and a paler bill and eye. The pinkish-white bill has fleshy flaps of skin hanging from the sides of its tip. The male’s call is an aspirated whistle, and the female’s is a rattling growl.[2] The Blue Duck is born with a green beak for just 8 hours after birth; where it then develops to its final colour.

Listen to the sound of Blue Duck

[audio:http://www.planetofbirds.com/MASTER/ANSERIFORMES/Anatidae/sounds/Blue Duck.mp3]

Copyright remark: Most sounds derived from xeno-canto

recorded by –


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Range

Australasia : New Zealand. Hymenolaimus malacorhynchos was formerly widespread in New Zealand. Since European settlement, its range has become highly fragmented, such that it is largely confined to the forested mountain ranges of central North Island and western South Island

Habitat

Blue ducks are a river species, mostly confined to headwater catchments of rivers over parts of both the North and South Islands. Its presence in these sites should not be regarded as an indication of habitat preference. Rather it should be viewed as the result of a restriction to generally unmodified environments whose relative quality as blue duck habitat has yet to be determined. The river sections in which blue ducks are found today have high water quality, stable stream banks, low transport of fine or suspended sediments, standing (mostly) native riparian scrub or woodland, and a wide diversity and abundance of aquatic invertebrates. Blue ducks principally occupy a habitat in which food is available in adequate quantity year-round and other essential resources (shelter, nesting sites, broodrearing habitat) are present. Adult blue ducks are a sedentary and territorial with pair bonds maintained throughout the year and over several years. The male contributes active parental care.

Reproduction

Females have been observed to breed at 12 months of age, while the majority of males first attempt breeding in their second year. The breeding season commences as early as August, when the female begins to feed more avidly and for longer periods each day. The previous seasons nest site may be reused, especially if young were successfully fledged. Five or six white eggs are usually laid, although clutches as large as nine and as small as three have been found. Eggs weigh about 70g each, which is close to 10% of the females body weight and there is often a two day interval between laying of consecutive eggs of the clutch. Nests have been found in river-side caves, beneath clumps of flax or grass, in holes in the river bank and in hollow logs. Only the female incubates throughout the 35 day incubation period. while his mate incubates, the male defends the territory from intruding birds, usually locating himself at a site close to the nest. The female normally leaves the nest to feed with her mate during the early morning and late afternoon. When ducklings hatch they are immediately capable of battling strong currents and feeding themselves. Both adults guard the young throughout their 70-82 days of development to fledging. The adults have distinct roles; the female is always close to the young ducklings while the male often trails behind the brood, constantly on the alert for predators. When the ducklings are near fledging their parents interest in them starts to wane. At the same time the adults normally commence their annual moult, during which time they are flightless.The adults generally hide during the day and only emerge to feed under the cover of darkness. Throughout the late summer and early autumn the juveniles range up and down the river in search of living space. Many initially try to force their way in between the territories of established pairs. If they are not successful, they will disperse more widely within their natal catchment. Some movement of juveniles to adjacent catchments has also been recorded, e.g. in Hawkes Bay, birds have been recorded moving from the Apias River to the Makaroro River Q. Adams pers. comm.), and on the South Island, birds have crossed the main divide. Generally, blue ducks appear to be a reluctant dispersers, and settlement and breeding beyond the natal catchment appears to be rare.

Feeding habits

The main foods of blue ducks are freshwater invertebrates, principally the larvae of caddis fly, mayfly and stone fly. Freshwater snails and chironomid larvae are also eaten and there is one report of South Island birds eating fruits of stream-side plants (Harding, 1990). Most feeding occurs by dabbling or up-ending in riffles and occasionally by diving in white water areas. Blue ducks also feed for short periods during the night. Patterns of prey selectivity varied for blue ducks living on Manganui a te ao River, but Tricoptera larvae in the family Hydrobiosidae and in the genus Aoteapsyche (Hydropsychidae) ranked highly in the diet.

Video Blue Duck

httpv://www.youtube.com/watch?v=Zy1UFG_fRkM

copyright: Neil Robertson


Conservation

This species is listed as Endangered because it has a very small and severely fragmented population which is undergoing a rapid decline owing to a variety of factors, most notably the affects of introduced predators.
Grazing and clearance of waterside vegetation has decreased water quality and led to the species’s disappearance from lowland rivers. Introduced mammals take eggs, chicks and adults, and video-camaras have shown these are the main cause for the decline. Eggs are taken by brush-tailed possum Trichosurus vulpecula and occasionally by Weka Gallirallus austrailis whilst incubating females, chicks and eggs are predated by stoats, especially in beech mast years when rodent populations explode and then crash, causing stoat populations to increase concurrently. This has led to an unbalanced sex ratio in beech dominated catchments. Hydroelectric dams have altered the flow of some rivers, reducing available habitat. Poor dispersal reduces recolonisation and prevents mixing of nearby populations. Introduced trout may compete for food. Human activities on the rivers often cause significant disturbance.
Blue Duck status Endangered

Migration

Sedentary

Distribution map

Blue Duck distribution range map

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