Whio – threats and conservation

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.

Whio pair

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

Rights: Bubs Smith, Department of Conservation

Threats to whio

Predation

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.

Stoat hunting

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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.

Rights: Image courtesy of Nga Manu Images

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.

Conservation

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.

Pest trap

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

Rights: Manaaki Whenua – Landcare Research, CC BY 4.0

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.

Education

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