Justification of Red List Category
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.
National surveys and censuses estimated the population to number at least 1,200 mature individuals protected, however, the wider population is estimated to be 2,500 individuals in total. It is difficult to obtain an accurate population estimate due to the widespread nature of the rivers and streams they inhabit in remote areas of New Zealand.
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.
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 the central North Island and western South Island (Heather and Robertson 1997). No fossil records of whio have been found from New Zealand’s offshore islands which indicate that these habitats were historically unable to sustain whio populations (Worthy and Holdaway 2002). 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). Over the 2016 breeding season, census and surveys conducted across 26 management sites across New Zealand found a total of 558 pairs to be protected by predator control (Glaser 2016). 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). The whio range continues to diminish in areas outside of management (Glaser 2016).
Whio are 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 (Baille and Glaser 2005). Whio 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 500m 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 whio are in the upper trophic level of their ecological niche, they can be used as an indicator of riverine ecosystem health and completeness (Adams 1997). On occasion, whio 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). Whio 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 whio and waterfowl (Eldridge 1986).. Female whio 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 2015). Fledglings are also known to flock at the end of the breeding season where pair bonds can be formed (DOC 2016).
. 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 UnderwayThe 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.
Whio 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 DOC GIS experts have developed a state of the art national database to capture outcome results for trap catch and whio counts to accurately measure progress and spatially map change over time (DOC 2014).
Where sites use a combination of trapping and 1080 to manage pests, record numbers of fledglings have been observed (DOC 2014). There has been a considerable amount of effort to encourage community groups to participate in whio and river protection which has resulted in seven new Recovery Sites being set up. M?ori are taking an active role in whio 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 whio 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 7000 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 whio (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 2015). The Egmont National Park population is an example of population re-establishment (whio became locally extinct in 1945-48, (Notornis 2010), 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 whio protected to reduce their vulnerability to stochastic events (Scrimgeour 2015).
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 for whio (Gummer 2016). Whio have been used as an indicator species and nesting success has been monitored through BfOB operations. Results show that whio raise more fledglings or young after the first year of aerial 1080 treatment compared to stoat trapping alone (DOC 2016). DOC is working in partnership with TB Free NZ to deliver aerial 1080 operation over the Whirinaki Security Site to coincide with the whio 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
Benstead, P., Mahood, S., Martin, R, McClellan, R., Pilgrim, J., Stattersfield, A., Taylor, J. & Stringer, C.
Glaser, A. & Williams, M.
BirdLife International (2021) Species factsheet: Hymenolaimus malacorhynchos. Downloaded from http://www.birdlife.org on 16/01/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 16/01/2021.