Hymenolaimus malacorhynchos
| Kingdom |
Phylum |
Class |
Order |
Family |
| ANIMALIA |
CHORDATA |
AVES |
ANSERIFORMES |
ANATIDAE |
| Scientific Name: |
Hymenolaimus malacorhynchos |
| Species Authority: |
(Gmelin, 1789) |
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Common Name/s:
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Assessment Information
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| Red List Category & Criteria: |
Endangered
C2a(i)
ver 3.1
|
| Year Published: |
2008 |
| Assessor/s: |
BirdLife International |
| Reviewer/s: |
Mahood, S., Butchart, S. |
| Contributor/s: |
Williams, M. |
Justification:
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.
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| History: |
| 2006 |
– |
Endangered
|
| 2004 |
– |
Endangered
|
| 2002 |
– |
Endangered
|
| 2000 |
– |
Vulnerable
|
| 1996 |
– |
Vulnerable
|
| 1994 |
– |
Vulnerable
|
| 1988 |
– |
Near Threatened
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Geographic Range
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| Range Description: |
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 Island3, counts from 1980-1994 indicate populations of c.640 and c.580 pairs respectively, whilst in 2004-2005 a national census revealed less than 600 pairs14. Some formerly robust populations have disappeared entirely and the sex ratio is now highly skewed in favour of males14. The decline has been most acute in on South Island, and especially in areas dominated by beech14. Six populations have been monitored for 5-15 years: sharp declines, gradual increases and stable numbers have been documented, making overall trends unclear1.
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| Countries: |
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| Range Map: |
Click here to open the map viewer and explore range.
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Population
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| Population: |
Williams (2205) - the results of a national survey.
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| Population Trend: |
Decreasing
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Habitat and Ecology
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| Habitat and Ecology: |
It is now confined to rivers of medium to steep gradients with partial forest cover overhead, and vegetation to the water's edge2,5,10. It nests near steep stream banks, in caves, cavities, or under dense vegetation. It usually lays six eggs, and can breed in its first year. Each pair requires a territory of 0.7-1 km of river14. Territorial birds can live for six to seven years9. It roosts mainly in stable undercut banks, often in association with woody debris12. Its diet consists almost entirely of aquatic invertebrates, primarily caddisfly larvae7.
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| Systems: |
Terrestrial; Freshwater |
| Major Threat(s): |
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 decline1,15. 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 concurrently15. This has led to an unbalanced sex ratio in beech dominated catchments14,15. Hydroelectric dams have altered the flow of some rivers, reducing available habitat3. Poor dispersal reduces recolonisation and prevents mixing of nearby populations8. Introduced trout may compete for food3. Human activities on the rivers often cause significant disturbance1.
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Conservation Actions
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| Conservation Actions: |
Conservation Actions Underway
A captive population has been established and c.20 young are reared each year11. In 1987 and 1991, 12 birds were released at Egmot National Park on Mt Taranaki and further releases have been carried out annually (43 birds released up to 2005), breeding occurred for the first time in 2005-2006 when five pairs nested rearing two young4,13. Intensive predator control is now carried out in the release area, this has led to the loss of no birds since 200413. Operation Ark was launched in 2003, this constituted a paradigm shift in Blue Duck conservation and focusses on establishing five viable populations (of fifty pairs each) with an extensive network of predator traps at each site15. Recreational activities have been reduced or stopped in some sensitive areas. Modifications to river flow regimes appear to have improved productivity and increased population sizes in certain areas1. Research is ongoing to determine factors that most influence distribution. Genetic analyses of population fragments have been completed6.
Conservation Actions Proposed
Monitor short-term fluctuations and long-term trends of key populations. Continue to undertake research to assist conservation management. Use captive bred birds to re-stock declining populations in association with predator control. Implement Operation Ark. Protect existing habitat through legal protection and advocacy1.
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