Blue duck/whio
Image: Sabine Bernert ©

Introduction

The blue duck/whio is only found in New Zealand. It is a nationally vulnerable species and faces a risk of becoming extinct.

Highlights

Population: Under 3,000
New Zealand status: Endemic
Conservation status: Nationally Vulnerable
Found in: Clean, fast-flowing rivers in the North and South Islands
Threats: Habitat loss, predation, disturbance

In this section

Facts

The blue duck is one of a handful of torrent duck species worldwide. It is a river specialist which inhabits clean, fast flowing streams in the forested upper catchments of New Zealand rivers. They are endemic to New Zealand so are found nowhere else in the world.

Their Māori name is whio in the North Island or ko whio whio in the South Island which depicts the call of the male bird. They are a taonga (treasured) species. Māori have a strong cultural, spiritual, and historic connection with whio. 

Whio are believed to have appeared at a very early stage in evolutionary history, an ancient species of waterfowl. Their isolation in New Zealand has resulted in unique anatomical and behavioural features. They have evolved over thousands of years to live without threats of mammalian predators. This means whio have a very trusting nature and not wary, allowing close interaction with people in their natural environment.

Whio nest along the riverbanks. They are flightless during the moult period which makes them extremely vulnerable to attacks from stoats, cats, ferrets, and dogs. Their persistence can not be secured on off shore islands like many of endangered species. They are rarer than some species of kiwi.

The sight and sound of whio and the image of New Zealand's back-country waterways have been synonymous for a long time. Today the whio is acknowledged by New Zealand's back-country users as an iconic species.

Whio are an indicator of healthy rivers and streams, an icon of New Zealand's waterways and feature on our $10 note.

Uniqueness

It is one of only three species amongst the world's other 159 waterfowl that live year round on fast-flowing rivers. The others are found in South America and New Guinea.

In contrast to other waterfowl, blue ducks get all their food (consisting almost exclusively of aquatic insect larvae) from the fast moving rapids and riffles where they rear their young within home territories. They have developed very streamlined and unique anatomical features to help them thrive in a riverine environment.

Blue ducks historically resided throughout the river environment from lowland reaches to high alpine streams. However the middle-river habitats hold the larger population densities where productivity is much higher than in typical headwaters. It is likely therefore that the upper-river habitats where blue duck are mostly found today are not preferred but sub-optimal habitats.

Predator plague

Whio live in low densities along the linear habitat of the river in 1–5 km territories. They require a scale of management like no other species to ensure their survival.

Their vulnerability (particularly to stoat predation) requires the management of their threats to encompass entire catchments. The logistic of this scale of management can be extremely challenging and require significant resources to manage their threats.

Research in Te Urewera demonstrated that 90% of the nests failed in an area without predator control. It was also demonstrated that 46% of the females were killed during the moult period when they retreated up small side stream to avoid disturbance.

Research in the Ruahines and in Taranaki found that over 60% of the fledged juveniles died in areas outside of management. A sample of 154 whio deaths were recorded between 1989-2008, 89 of these deaths were linked to predators (58%), 24 natural deaths, 22 human causes and 19 were unknown. Of the 89 predator deaths 89% of these were identified to have been caused by stoats (N=79). Stoats have been identified as the number one predatory agent causing whio declines.

Blue duck/whio is at real risk from a predator plague caused by high levels of seed production ('beech mast') in 2016 which will increase the level of predation.

Our work

Battle for our Birds protects whio and other native species from predators.

We run blue duck/whio conservation management projects to protect this rare species.

The Blue duck/whio recovery plan 2009-19 focuses on the retention of viable wild whio populations throughout their nature range.

Whio Forever

Genesis Energy is partnering with DOC to help save the whio through the Whio Forever Project. Genesis' contribution over the next five years will ensure that all aspects of the Whio Recovery Plan 2009-2019 can be implemented.

This partnership will effectively secure the species by protecting priority populations so they grow, encouraging participation of the community and increasing New Zealanders understanding of the link between the whio and river health.

Genesis is also providing technical expertise and staff support for  raising the profile of whio.

Territory

Blue duck establish exclusive territories along 1-5 km of river (depending on surround pair densities). Strong pair bonding results in individual pairs occupying the same stretch of river year after year which they aggressively defend against other blue duck, as well as grey duck, paradise duck and even shags or gulls.

Blue ducks vigorously defend their river territories all the year round. They flying up and down the river on evening like low level fighter pilots chase other whio out of their territory. 

The size of each pair's territory can vary (average is about 1.5 km) depending on the quality of the habitat, roosts and food available.

Blue duck territory generally encompasses tributaries or small side streams which they will retreat to during floods, draughts and when they are in moult.

Blue duck are forever watchful looking to the sky for avian threats and will always see you before you see them and the male will sound the alarm call.

The larger (1,000-1,200 g) males can live for up to 12 years but smaller (800–1,000 g females are generally much shorter lived.

Location

The pre-European fossil record suggests that blue duck were once throughout New Zealand. They are currently considerably less widespread being limited to the less modified catchments of the Urewera, East Cape and central areas of North Island, and along the West Coast of South Island from Nelson to Fiordland.

There is growing concern for the species as most studies suggest that this already reduced range is continuing to contract. Remaining populations tend to be fragmented and isolated, have low reproductive success and are increasingly dominated by males. It is estimated that about 640 pairs remain on North Island while just under 700 pairs remain on South Island giving a total population of between 2,000 and 3,000.

Physical features

  • Blue ducks have unique features such as streamlined head and large webbed feet to enable them to feed in fast moving water.
  • The upper bill has a thick semicircular, fleshy 'lip' that overlaps the lower bill allowing them to remove  insect larvae off the rocks that that they cling to , without wear and tear.
  • The male makes a distinctive high-pitched aspirate sound – “whio”, contrasting with the guttural and rattle-like call of the female.
  • Whio are very camouflaged to evade avian predators such as falcon and harriers
  • Adult length: 530mm; males are between1000 -1200g; females between 800-1000g
  • Blue ducks moult between December and May.
  • They are mainly active during early morning and late evening periods, hiding during the day in log-jams, caves and other such places – some populations have adopted an almost nocturnal existence.
  • Blue duck are very good parents and continually watch over their young as they feed independently near the water's edge.
  • Juvenile fledglings can disperse up to 80 km from where they were born.
  • Fledglings flock together towards the end of the breeding season where they can be found in large groups. It is thought that this is where they find their mates.

Behaviour

Blue duck use the river as a defence mechanism to evade threats, going with the flow, submersing themselves and retreating into roosts.

Nesting

Blue ducks nest between August and October, laying 4-9 creamy white eggs. The female incubates the eggs for 35 days and chicks can fly when about 70 days old.

Nesting and egg incubation of four to seven eggs is undertaken by the female while the male stands guard. Nests are shallow, twig, grass and down-lined scrapes in caves, under river-side vegetation or in log-jams, dry punga fronds and toi toi. are therefore very prone to spring floods.

Nesting blue duck are especially vulnerable to predation by animal pests such as stoats. These nesting sites are in area where stoats commonly feed.  Stoats can easily be find the nest by either follow the scent trail of the female to her hiding place or sniff out the nest through scent that is carried on the breeze blowing up and down the river.

Habitat

Blue duck require bouldery rivers and streams within forested catchments which provide high water quality, low sediment loadings, stable banks, over head canopy cover and abundant and diverse invertebrate communities.

With such habitat requirements, blue duck are key indicators of river system health. The higher the number of breeding pairs of blue duck on a given stretch of river, the greater the life supporting capacity of that river.

The blue duck have adapted to thrive in one of New Zealand's harshest environments. This environment is prone to catastrophic flood events which can change the river morphology, fragment broods, wash away their food source and force them into side stream where they lose the water as their first defence.  This unmanageable threat can have an extreme impact on breeding success from one year to the next which has been demonstrated to have had a significant impact on whio populations throughout the country.  

Threat classification

The DOC species threat classification of blue duck/whio is Nationally Vulnerable.

Blue duck are recorded by the International Union of Conservation for Nature (IUCN) 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.

Find out more about threats to whio and how you can help.

Sound recording

Blue duck/whio song (MP3, 1,342K)
1 minute 24 second recording of a blue duck/whio adult pair swimming in a stream communicating and answering tape recorded calls.

Note: Right-click the song link for options to save. Bird songs may be reused according to our copyright terms. More help on files.

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