Hymenolaimus malacorhynchos 


Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Aves Anseriformes Anatidae

Scientific Name: Hymenolaimus malacorhynchos
Species Authority: (Gmelin, 1789)
Common Name(s):
English Blue Duck
Hymenolaimus malacorhynchus malacorhynchus Collar et al. (1994)
Taxonomic Source(s): del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Lynx Edicions BirdLife International.
Taxonomic Notes: A genetic assessment of Blue Duck concluded that the North Island and South Island populations show a level of lineage separation and should be treated as separate management units for conservation purposes (Robertson et al. 2007)
Identification information: 53 cm. Blue-grey duck with pale pink bill. Mottled reddish-brown breast. Yellow eye. Juvenile has less speckling on breast, and has a grey bill and eye. Voice Male, fee-o. Female, rattling growl.

Assessment Information [top]

Red List Category & Criteria: Endangered C2a(i) ver 3.1
Year Published: 2013
Date Assessed: 2013-11-01
Assessor(s): BirdLife International
Reviewer(s): Butchart, S.
Contributor(s): Williams, M.
Facilitator/Compiler(s): Benstead, P., Mahood, S., Martin, R, McClellan, R., Pilgrim, J., Stattersfield, A., Taylor, J.
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 effects of introduced predators.

Previously published Red List assessments:
2012 Endangered (EN)
2008 Endangered (EN)
2006 Endangered (EN)
2004 Endangered (EN)
2002 Endangered (EN)
2000 Vulnerable (VU)
1996 Vulnerable (VU)
1994 Vulnerable (VU)
1988 Near Threatened (NT)

Geographic Range [top]

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 Island (Heather and Robertson 1997). The most recent population estimate is given as 2,500-3,000 individuals with a maximum of 1,200 pairs (Whio Recovery Group, in Glaser et al. 2010), although in 2005 Williams (in Wilson et al. 2005) considered that the actual breeding population was unlikely to exceed 600 pairs (although it is not clear what this figure is based upon). In contrast a recent estimate was more positive, considering that approximately 640 pairs remain on the North Island and 700 pairs on the South Island (Young 2009). The largest numbers are found in rivers and streams in the catchments of the Bay of Plenty, the central North Island, Northwest Nelson, the West Coast and Fiordland (Whio Recovery Group, in Glaser et al. 2010). An exhaustive survey in Arthur's Pass National Park using dogs found only 6 individuals in February 2011, down from around 50 in the early 1980s (Langlands 2011).

Countries occurrence:
New Zealand
Continuing decline in area of occupancy (AOO): Yes
Extreme fluctuations in area of occupancy (AOO): No
Estimated extent of occurrence (EOO) - km2: 54800
Continuing decline in extent of occurrence (EOO): Yes
Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: Yes
Extreme fluctuations in the number of locations: No
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: A national survey estimated the population to number at least 1,200 mature individuals, roughly equivalent to 1,800 individuals in total.

Trend Justification:  Declines in both distribution and abundance with the result that the species is now restricted to fragmented populations (Whitehead et al. 2008). The overall population is thought to be declining, especially on the South Island (Glaser et al. 2010). Positive population responses have been observed where predator control has taken place, including a 2.8-fold population increase in 4 years with 3 fledged young per pair each year and 94% chick survival (Glaser et al. 2010). In contrast, unmanaged sites had a 91% nest failure rate and productivity was 0.64 fledged young per pair per year (Glaser et al. 2010), clearly indicating that the species is declining in areas without management intervention. The most recent Species Recovery Plan (Glaser et al. 2010) considered that 215 pairs occur in locations that have some form of protection.
Current Population Trend: Decreasing
Additional data:
Number of mature individuals: 1200 Continuing decline of mature individuals: Yes
Extreme fluctuations: No Population severely fragmented: Yes
No. of subpopulations: 2-100 Continuing decline in subpopulations: Unknown
Extreme fluctuations in subpopulations: No All individuals in one subpopulation: No
No. of individuals in largest subpopulation: 1-89

Habitat and Ecology [top]

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 edge (Marchant and Higgins 1990, Collier et al. 1993, M. Willliams in litt. 1999). 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 river (Williams 2005). Territorial birds can live for six to seven years (Williams 1991). It roosts mainly in stable undercut banks, often in association with woody debris (Baille and Glaser 2005). Its diet consists almost entirely of aquatic invertebrates, primarily caddisfly larvae (Veltman et al. 1995).

Systems: Terrestrial; Freshwater
Continuing decline in area, extent and/or quality of habitat: Yes
Generation Length (years): 7.1
Movement patterns: Not a Migrant

Threats [top]

Major Threat(s): Predation of eggs, young and incubating females by stoat Mustela erminea was found to be the most significant threat to the species at least in Fiordland (Whitehead et al. 2008), but also probably across the rest of the species's range (Glaser et al. 2010). Eggs are also taken by brush-tailed possum Trichosurus vulpecula and occasionally by Weka Gallirallus australis (Adams et al. 1997). The greatest predation pressure occurs in cycle with beech mast years, as rodent populations explode, causing a lagged increase in stoat populations which seek alternative prey when rodent numbers crash (Whitehead et al. 2008). A male-biased sex-ratio has been observed throughout the range, indicating that predation during incubation (which is almost exclusively carried out by the female) is significant (Glaser et al. 2010). Previously, grazing and clearance of waterside vegetation decreased water quality and led to the species's disappearance from lowland rivers. Hydroelectric dams have altered the flow of some rivers, reducing available habitat (Heather and Robertson 1997), but increases in flow rates implemented from 2004 have mediated some of the impacts (Stier 2008). Poor dispersal reduces recolonisation and prevents mixing of nearby populations (Williams 1988). Introduced trout may compete for food (Heather and Robertson 1997), and birds caught in discarded fishing line have been reported (Young 2009). Human activities on the rivers often cause significant disturbance (Adams et al. 1997), and sub-division of land for development has recently occurred adjacent to rivers occupied by the species (Young 2009, Young 2010). The introduced alga Didymo may reduce habitat quality, and an avian diseases have the potential to significantly impact populations if introduced (Glaser et al. 2010).

Conservation Actions [top]

Conservation Actions: Conservation Actions Underway
Two co-ordinated management programmes are underway involving Hymenolaimus malacorhynchos, Operation Ark and Whio Operation Nest Egg (WHIONE) (Glaser et al. 2010). Operation Ark was initiated in 2003 to target a suite of species occurring in Nothofagus forests, including this species. Initially this focused on establishing five viable populations (of fifty pairs each) with an extensive network of predator traps at each site (Williams 2006). WHIONE is a programme where breeding pairs are closely monitored and eggs removed for hatching in captivity before being returned once the chicks are at a lower risk of predation, and has proven very effective at rapidly increasing numbers (Glaser et al. 2010). Both of these programmes occur alongside large-scale control of predators in the release locations. Numbers in managed areas had increased three-fold after 4 years (Bain 2008). A captive population has been established on the North Island (Whio Forever Project) and c.20 young are reared each year (Anon 2004). 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) (Caskey and Peet 2005), breeding occurred for the first time in 2005-2006 when five pairs nested rearing two young (Hutchinson 1998, Biswell 2006). Intensive predator control is now carried out in the release area, this has led to the loss of no birds between 2004 and 2006 (Biswell 2006). 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 areas (Adams et al. 1997). Research is on-going to determine factors that most influence distribution. Genetic analyses of population fragments have been completed (Triggs et al. 1992).

Conservation Actions Proposed
Establish eight Security Sites with the aim to secure at least 50 pairs in each, hence a secure population of 400 pairs, using a combination of aerial 1080 poisoning and stoat trapping to control predators and using WHIONE to increase populations (Glaser et al. 2010). Establish a series of Recovery Sites across the range of the species that can be managed in conjunction with communities or have existing management in place (Glaser et al. 2010). Monitor population trends in locations where predator control is carried out and carry out close-monitoring to identify the agents of decline in areas other than Fiordland (Glaser et al. 2010). Continue to undertake research to inform conservation management. Use captive-bred birds to continue to re-stock declining populations on the North Island. Protect existing habitat through legal protection and advocacy (Adams et al. 1997). Include local communities in advocacy activities; ensure information is shared effectively and include local people in protection activities (Glaser et al. 2010). Establish protocols to prevent the introduction of Didymo or avian disease into new catchments.

Citation: BirdLife International. 2013. Hymenolaimus malacorhynchos. The IUCN Red List of Threatened Species 2013: e.T22680121A47992345. . Downloaded on 30 November 2015.
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