Whio in decline…
The whio (blue duck) is one of New Zealand’s ancient endemic waterfowl species and is classified as Threatened (Nationally Vulnerable) in the New Zealand Threat Classification System 2012, and listed as Endangered on the IUCN Red List of Threatened Species.
North Island and South Island whio populations are genetically distinct (though they are not described as sub-species) and are treated as separate management units. The whio has experienced rapid declines (particularly in the South Island) in abundance and distribution, nowhere common. It lives at low densities in severely fragmented populations. The most recent estimate of total population numbered 1200 pairs at most.
The most notable decline driver comes from introduced mammalian predators, with predation of eggs, young and incubating females. Stoats are the most significant threat and stoat control is a main focus of management activities.
The blue duck’s widespread decline throughout South Island beech forests areas has highlighted the insidious effects of mast-seeding beech trees, which result in great predation pressure, as rodent populations explode, causing a lagged increase in stoat populations which seek alternative prey when rodent numbers crash. A malebiased sex-ratio throughout the range, indicates that predation during incubation is significant.
One of the major conservation management tools for whio is captive breeding for release into the wild. The blue duck has been held in captivity for many years, and its husbandry requirements are understood. The aim is to maximise productivity of the captive breeding programme, and ensure that captive-bred ducklings are released at the highest priority sites. Captive breeding has proven highly effective, and is vital in aiding the recovery programme with the re-establishment and rebuilding of viable populations throughout the former range.
The Isaac Conservation and Wildlife Trust provides the largest output of blue duck juveniles annually, with its waterfowl aviaries being the most successful captive breeding enclosures in New Zealand for North Island blue duck. The Trust currently holds two North Island blue duck breeding pairs. These breeding pairs can lay up to three clutches per season, with an average of six eggs per clutch. All eggs are collected for incubation and hand rearing.
The Trust is a significant participant in the WHIONE programme, which consists of retrieving wild eggs each breeding season from South Island pairs for artificial incubation and rearing in captivity, with a subsequent release of juveniles once fledglings have been hardened in our fast water facilities and are at a lower risk of predation. Releases take place in natal territories or at new sites around the South Island to increase numbers and genetic diversity across sites or re-establish lost populations. Since 2016 the Trust has been retaining cohorts of South Island blue duck juveniles for flock mating, to initiate a captive breeding population across several South Island facilities. The Trust will move out of North Island birds and hold three pairs of the South Island blue duck.
Each season for the last 12 years, the Trust has also received North Island blue duck juveniles bred by other captive institutions nationwide, which are transferred for pre-conditioning in fast flowing raceways prior to release into the wild.
Wildlife Project Administrator
The Isaac Conservation and Wildlife Trust