Threatened ducks increase by 151 per cent in eight NZ rivers since 2011

Thursday, 16 July 2020

People walking near rivers in New Zealand are far more likely to see whio than in the past.

Pairs of threatened whio (blue ducks) have increased by 151 per cent at sites where restoration work has been under way since 2011.

The whio is a threatened species of native duck only found in New Zealand’s fast flowing waters. Featured on New Zealand’s $10 note and with an estimated nationwide population of less than 3000 birds, whio are rarer than kiwi.

There are now 748 pairs of whio in eight rivers across New Zealand, up from 298 pairs in 2011 when the Department of Conservation (DOC) and Genesis started working together to restore populations of whio.

The eight security sites across New Zealand where whio populations are managed intensively with predator control and breeding assistance programmes span from Te Urewera in the North Island to Fiordland in the South.

Whio chicks take refuge beside a stream in Taranaki. Whio numbers increased 70 per cent in the region during the last breeding season.

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Young whio/blue ducks have their first swim at Christchurch's Orana Wildlife Park. (Video first published in December 2019)

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DOC’s Western South Island operations director and a member of the Whio Forever management committee Mark Davies said the result was “very fulfilling”.

“Even this year, with a drama-filled season of severe flooding which can wipe out nests on river beds and margins, a mega beech mast season and predator control delays due to Covid-19, the population has grown by 23 pairs,” he said.

Genesis' wholesale operations executive general manager Nigel Clark said the result was driven by the hard work of individual trappers, privately run trusts and businesses that hold whio breeding pairs, hatch whio eggs and raise their chicks.

The whio are predated by stoats, ferrets and cats with the largest impact during nesting time when eggs, young and females are vulnerable, and also when females are in moult and can’t fly.

Whio cannot be moved to predator-free islands like other species because of their reliance on fast-flowing rivers.

Pairs occupy approximately 1km of water – so they need a lot of river to sustain a large population and they fiercely defend their territories, which makes it difficult to put them with other ducks in captivity.