Data Zone
Justification of Red List category
This species has a small population that is inferred to be declining primarily due to the effects of introduced predators, with no subpopulation exceeding 250 mature individuals. It is therefore classified as Endangered.
Population justification
The five-yearly census of managed sites in 2021 counted 863 pairs: 491 pairs on the North Island and 372 on the South Island (DOC 2022), equating to approximately 1,700 mature individuals. It is difficult to obtain an accurate global population estimate due to the widespread nature of the rivers and streams that the species inhabits in remote areas of New Zealand, but the wider population is not thought to exceed 2,500 mature individuals and is placed here in the range 1,500-2,499 mature individuals. 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), and the largest subpopulation at Tongariro numbers slightly more than 100 pairs (DOC 2022).
Trend justification
There are declines in both distribution and abundance with the result that the species is now restricted to disjunct populations (Whitehead et al. 2008). The overall population is thought to be declining especially on the South Island (Glaser et al. 2010). Survival studies conducted at three security sites; Northern Fiordland (Whitehead et al. 2008), Te Urewera (Glaser and Allerby 2010) and Wangapeka (DOC 2014a) demonstrate potential declines associated with predator impacts and weather events (Simpkins et al. 2015).
Population modelling indicates ongoing decline in the absence of management (Scrimgeour 2015a). Positive population responses have been observed where predator control has taken place, including a 2.8-fold population increase in four years with three 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), suggesting that the species is declining in areas without management intervention. The population is suspected to be declining at a rate equivalent to 10-30% in three generations as non-managed sites continue to experience high levels of predation, and this is thought to be ongoing (Robertson et al. 2021).
Hymenolaimus malacorhynchos was formerly widespread in New Zealand. Since European settlement, its range has become fragmented, such that it is largely confined to the forested mountain ranges of the central North Island and western South Island (Heather and Robertson 1997). No fossil records have been found from New Zealand’s offshore islands, which suggests that these habitats were historically unable to sustain populations (Worthy and Holdaway 2002).
This species is reliant on high quality, stable rivers and stream catchments. They are 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). They roost mainly in stable undercut banks, often in association with woody debris (Baillie and Glaser 2005). They can utilise a wider area surrounding their territories such as tributaries and small side streams on a regular basis for roosting, foraging and during the moult. Adult moulting females have been recorded in small streams 3.5 kilometres from their territory in small seeps at altitudes of 500 m above sea level (Glaser and Allerby 2010). Side streams are also frequented during floods and droughts to obtain food and during the moult to grow their new plumage.
The diet consists almost entirely of aquatic invertebrates, primarily caddisfly larvae (Veltman et al. 1995). Because Blue Duck are in the upper trophic level of their ecological niche, they can be used as an indicator of riverine ecosystem health and completeness (Adams et al. 1997). On occasion, they will feed on fruits of alpine riparian shrubs (Harding 1990) and birds have also been observed foraging in surrounding native bush for berries (A. Glaser pers. obs.).
They nest near steep stream banks, in caves, cavities, or under dense vegetation. They usually lays six eggs, and can breed in their 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), during which time they fiercely defend their territories from other individuals and waterfowl (Eldridge 1986). Females incubate the eggs while the male defends the territory. Ducklings are self-reliant and capable of battling strong currents from hatching. Both adult birds guard the young over the 70-82 days that it takes for ducklings to fledge (Adams et al. 1997). Populations that have had effective management over time have territories as small as 0.2 km per pair (Swanney 2014). Fledglings are also known to flock at the end of the breeding season where pair bonds can be formed (DOC 2022).
Blue Duck are affected by a wide range of threats. These include natural and introduced predators, human-induced threats and stochastic environmental and weather events (Riddler 2009).
The species is susceptible to a variety of introduced predators such as feral cats Felis catus, rats Rattus spp, stoats Mustela erminea, ferrets Mustela furo, weasel Mustela nivalis vulgasis, dogs Canis familiaris and Brush-tailed Possum Trichosurus vulpecula. They are also vulnerable to natural predators such as weka Gallirallus australis, Swamp Harrier Circus approximans, New Zealand Falcon Falco novaeseelandiae and eels Anguilla dieffenbachia (Adams et al. 1997, Glaser et al. 2010). Predation of eggs, young and incubating females by stoats was found to be the most significant threat to the species in Fiordland (Whitehead et al. 2008), and across the rest of the species' range (Glaser et al. 2010). Nesting failure in untreated environments has been recorded to be as high as 91% which has largely been attributed to stoat predation (Glaser and Allerby 2010). 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). Stoat predation has also been attributed to 46% female mortality during moult when birds retreat to small tributaries during this flightless period (Glaser and Allerby 2010). Nesting success has been shown to be very high following predator control before dropping in subsequent years, and is higher with increasing distance to the interior of treatment blocks (Steffens et al. 2022).
Human-induced impacts such as road fatalities, shooting, wire-strikes and management manipulations during catching and handling also directly impact the species (Riddler 2009). Previously, grazing and clearance of waterside vegetation decreased water quality and led to the species disappearing from lowland rivers. Hydroelectric dams have altered the flow of some rivers, reducing available habitat (Heather and Robertson 2015), but increases in flow rates implemented from 2004 have mediated some of the impacts (Stier 2008). The Tongariro Power Scheme’s Western Diversion Rivers has completed surveys since 1998 to assess the effectiveness of minimum flows established in 2004. The total number of pairs has almost quadrupled since 1998 (to 30 pairs in this reach). Pair densities are now very high in some reaches, with the average territory length on one of the Whanganui Reaches being just 170 m per pair. Stability through both the winter and breeding season results in high invertebrate abundance which assists with body conditioning and rearing. This in combination with predator control through aerial 1080 operations (by TB Free New Zealand bovine TB control programme and Department of Conservation) as well as predator trapping has reduced the threats (Swanney 2014).
Poor dispersal in some catchments reduces recolonisation and prevents mixing of nearby populations (Williams 1988). A high percentage of mortality (66%) in juvenile fledglings during the transient period of establishing new territories has been documented in the Ruahine Forest Park in the absence of predator control (Glaser in litt. 2016). Fledglings can travel up to 20.5 km from their point of natal origin, across catchments to the extent of suitable forested habitat into unprotected environments (Glaser 2003). Difficulty in linking catchments due to the high level of conservation management required by the species means many populations are vulnerable to isolation and genetic bottlenecks over time (A. Glaser in litt. 2022). Introduced trout Salmo trutta may compete for food (Heather and Robertson 2015), 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). The introduced alga Didymo may reduce habitat quality, and avian diseases have the potential to significantly impact populations if introduced (Glaser et al. 2010). The species' vulnerability to catastrophic events has also been documented over the years. Avalanches, slips, lahars and flood events can fragment broods, reduce food availability and cause individuals to move into small side streams where they lose their natural defence of escape through the water (Glaser and Allerby 2010). The combination of predation by introduced species and anthropogenic climate change causing severe flood events indicated that the species has only a limited probability of persistence during the next 100 years. Importantly, the additive effects of population losses due to predation and a rising frequency of floods (as predicted by general circulation models) increases extinction risk by 69% (Simpkins et al. 2015).
Conservation Actions Underway
The Department of Conservation’s Whio Recovery Programme has established a partnership agreement with Genesis Energy over the past five years (2011-2016) to fast track the Whio Hymenolaimus malacorhynchos Recovery Plan 2009-2019. Genesis Energy made a considerable contribution of $2.5 million as well as additional internal resources and expertise to meet the Whio Recovery Plan goals and actions.
Blue Duck are now secured at eight "Security Sites" (four in the North Island and four in the South) as an outcome of this partnership. Managed populations are recovering nationally through the effective use of over 5,000 stoat traps along more than 1,400 km of river. There are now more than 558 pairs protected and the population is growing within the managed sites. This has exceeded the Recovery Plan’s short term goal of 500 pairs to be protected, 400 at Security sites and 100 at Recovery sites. Some Security Sites are still working towards their 50 pair targets while others have exceeded this. Genesis Energy and leading GIS experts from the Department of Conservation have developed a state of the art national database to capture outcome results for trap catch and counts to accurately measure progress and spatially map change over time (DOC 2014b).
Where sites use a combination of trapping and 1080 to manage pests, record numbers of fledglings have been observed (DOC 2014a). There has been a considerable amount of effort to encourage community groups to participate in Blue Duck and river protection which has resulted in seven new Recovery Sites being set up. M?ori are taking an active role in management: an example of this is Ngai Tuhoe taking up their role as katiaki in Te Urewera. There has also been a focus on increasing the public’s awareness of this iconic species nationally and helping New Zealanders understand the link between the species and healthy rivers. Genesis Energy has created the “Whio Forever” brand, website and social media to engage and educate people through these medium. There is an increased advocacy focus through events such as Whio Awareness month in March with online competitions and the Whio family fun weekend at Auckland Zoo where 7,000 people attend each year. The Recovery Programme now has clear direction through a shared Communication Plan which identifies strategic direction for increasing advocacy associated with the species (Buck 2016). New primary education resources have been developed to provide teachers with classroom ready resources to educate students across the curriculum.
The Breed for Release programme continues to support the augmentation of populations through the use of captive bred birds from both the North and South Islands (Scrimgeour 2015b). The Egmont National Park population is an example of population re-establishment (the species became locally extinct in 1945-48), through the release of 165 birds (Gummer 2016). A 2015 census of the Egmont National Park Recovery Site found a total of seven single adults and 33 pairs which had produced a minimum of 25 fledglings that season. Thirty-six unknown birds (without transponders) were also found, which indicate wild born juveniles (King 2015). Whio Operation Nest Egg (WHIONE) is a programme where breeding pairs are closely monitored and eggs removed for hatching in captivity, with chicks returned to the wild once they 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. Although population modeling showed that most of the North Island sites were on a positive trajectory, further supplementation through a South Island Breed for Release programme is being considered to increase the number of individuals protected to reduce their vulnerability to stochastic events (Scrimgeour 2015b).
The Whio Recovery Programme continues to work with other landscape-scale animal pest operations such as TB free and Battle for our Birds (BfOB) to use the synergy of protection that large-scale aerial 1080 drops provide (Gummer 2016). Blue Duck have been used as an indicator species and nesting success has been monitored through BfOB operations. Results show that Blue Duck raise more fledglings or young after the first year of aerial 1080 treatment compared to stoat trapping alone (DOC 2022). The Department of Conservation is working in partnership with TB Free NZ to deliver aerial 1080 operation over the Whirinaki Security Site to coincide with the breeding season (Morton 2015).
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 ongoing to determine factors that most influence distribution. Genetic analyses of population fragments have been completed (Triggs et al. 1992) but more detailed analysis of regional variation is required (Gummer 2016).
The platform for the Whio Recovery programme has now been set through Genesis Energy’s investments to grow the population and increase profile and awareness (Glaser 2016).
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.
Text account compilers
Vine, J.
Contributors
Glaser, A. & Williams, M.
Recommended citation
BirdLife International (2024) Species factsheet: Blue Duck Hymenolaimus malacorhynchos. Downloaded from
https://datazone.birdlife.org/species/factsheet/blue-duck-hymenolaimus-malacorhynchos on 27/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 27/12/2024.