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  • Whio/blue ducks were once commonly found on rivers and streams throughout mainland New Zealand. However, the populations are now severely restricted and isolated from each other. Recent estimates suggest there may be as few as 2,500 birds remaining in the total population.

    Whio are a protected species and are classified as endangered by the IUCN and are listed as nationally vulnerable in the New Zealand Threat Classification System.

    Rights: Bubs Smith, Department of Conservation

    Whio pair

    Whio stay together as monogamous pairs and usually hold the same territory for life.

    Threats to whio


    Predation is one of the two major threats to whio. Whio – especially the chicks – are subject to predation as part of natural food webs that include species such as the morepork/ruru, harrier hawk/kāhu, weka, New Zealand falcon/kārearea and longfin and shortfin eel/tuna. In earlier times, other large avian predators possibly also preyed upon adult whio.

    However, the introduction of new predators has seen a significant negative impact on whio numbers. Now predation is estimated to account for more than 80% of the whio’s decline. Stoats, ferrets, possums, feral cats and dogs prey especially upon eggs, chicks and ground-nesting females. Due to this, there are now more male whio than female.

    Whio moult from February until May every year, replacing a significant proportion of their feathers over this time. In the pre-predator environment, whio were safe during the moult as they hid away in their roosts and nests during the day. However, since the introduction of mammalian predators, the moulting season is an even more vulnerable time for whio, as the loss of feathers reduces their ability to fly away from danger, and the predators can access their nests.

    Rights: Image courtesy of Nga Manu Images

    Stoat hunting

    The stoat is a swift hunter and will scavenge empty or abandoned nests. They are also known to attack prey much larger than themselves and have had devastating effects on the kiwi population.

    As they occupy such a unique ecological niche, whio are vulnerable to any habitat alteration.

    Habitat loss

    Habitat loss is the other major factor causing the decline in whio numbers. The amount of suitable habitat has reduced significantly over the last century, due largely to human modification – particularly through changing land and water use. It is estimated that only 1% of the whio’s original habitat still exists. Urbanisation, deforestation, agriculture, river diversion, decline in water quality and human recreation have all adversely affected the waterways where whio live.

    As they nest in burrows and caves along the river bank, whio are also highly vulnerable to flooding. Floods can destroy or wash away nests, change the shape of the river, separate families, wash away food sources and wash away or drown ducklings. Floods also force whio up onto the banks and alongside streams where they can become more vulnerable to predators.

    All these threats have an extreme impact on breeding success and a significant impact on whio populations.


    Unlike some endangered bird species, whio cannot simply be transferred to offshore islands, because they rely on fast-flowing river habitats that are unavailable on islands. The continued survival of this species is therefore dependent on the protection of secure wild populations throughout mainland New Zealand.

    In 2009, the Department of Conservation started a 10-year recovery programme to protect whio. The plan includes working in partnership with other groups. For example, the Whio Forever programme was conceived and implemented in partnership between the Department of Conservation and Genesis Energy. Other examples include the Manganui o te Ao River Whio project, funded by the Central North Island Blue Duck Conservation Charitable Trust and the Blue Duck Station project.

    These projects include several approaches to whio conservation. For example, the Arahura River site on the West Coast, sponsored by Solid Energy, is one of eight national security sites, and management at this site consists of stoat trapping and captive rearing.

    Predator control

    Predator control programmes involve the systematic use of predator traps. Stoats have been identified as the most significant predator of whio, and much of the decline in chick numbers is due to them. Substantial whio population increases have occurred in selected areas where persistent and extensive riverside predator con​trol has been practised.

    Rights: Manaaki Whenua – Landcare Research, CC BY 4.0

    Pest trap

    This variety of trap is effectively used in New Zealand to control stoats, rats and hedgehogs.

    Monitoring programmes

    Tagging and tracking whio using tools such as banding, microchipping and radiotransmitters allows scientists to monitor numbers of whio and track where they go.

    WHIONE (Whio Nest Egg) programme

    This involves moving whio eggs from wild nests early in the breeding season to allow wild pairs to re-nest and raise their ducklings. The eggs collected are taken to captive rearing facilities where they are incubated, hatched and reared to a survivable weight, then released again.

    Captive breeding

    North Island whio are held and bred on both main islands of New Zealand and the offspring are returned to their respective island. South Island whio are held and bred in captivity on the South Island only.


    The development of a range of educational resources about whio includes the Whio Forever resources.

    Related content

    Examples of related articles on the Science Learning Hub include Whio – the blue duck, Whio adaptations, Fantastic whio feathers, Conserving native birds – introduction, Conserving native birds – writer’s insight, Predation of native birds and Predator Free 2050 vision.

    There are also several teacher PLD sessions related to this topic: Bird conservation and literacy, SLH and conservation, Diving into inquiry with whio, Why learn about whio?, Inquiry outside the classroom and Taking action for conservation.

    We also have PLD webinars to support student action and investigation: Eco-explorers and Pest detectives.

    Activity ideas

    Some other activities on the Science Learning Hub related to whio and other New Zealand ducks that you may wish to explore include Ethics in bird conservation, Eliciting prior knowledge, Whio feathers – what are they for?, Whio habitats and conservation and Ethics in conservation science.

    Useful links

    For more detailed information about the whio/blue duck and New Zealand birds in general, you may want to visit Whio Forever, New Zealand Birds Online, New Zealand Birds, Department of Conservation, Wetland birds or 10,000 Birds.

    To view a selection of our resources and related 3rd party materials on predator control and conservation, check out our Pinterest board, Predator Free NZ.

    The Department of Conservation 'Conservation blog' highlights some of the work they do. This blog post is about success in the Whione programme in the Kahurangi National Park.

    Posters are a great way of accessing small chunks of information in a very visual way. These Facts about the whio posters produced by DOC are in both English and Te reo Māori and provide a great starting point for finding out more about one of our most unique endemic birds.

    In 2022, results from a 7-year Department of Conservation study into combined predator control methods revealed great news for the survival of our native whio, showing that 1080 used alongside trapping can help control introduced predators. Read about it on the Predator Free New Zealand website, which includes a link to the original research paper.

      Published 6 August 2017 Referencing Hub articles
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