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Native animals

Blue duck/whio

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Threats

Threats to blue duck/whio

Habitat loss

Historically, one of the major causes of blue duck decline was habitat loss. Forest clearance for agriculture and poor riparian (river-side) management resulted in reduced water quality. In many other rivers, flows are now manipulated for hydro-electric power generation or irrigation, which has changed the characteristics of the rivers making them unsuitable for blue duck.

Predators

Whilst habitat loss still remains a threat to blue duck, other threats are also very important.

Even where high quality river habitat remains, predation by introduced mammalian predators is now playing a significant role in the decline of the species.

Stoats are perhaps the greatest danger. They attack females on the nest, steal eggs, and take young ducklings from the river's edge.

Feral cats, domestic dogs and ferrets are also known predators of blue duck, while rats and possums have been recorded at nests and are likely to take eggs.

Human disturbance

Another as yet un-quantified threat to blue duck is human disturbance. As New Zealand and overseas tourists increasingly utilise wilderness rivers for recreational activities, like white water rafting and kayaking, there is some evidence that disturbance of family groups during the breeding season may have an adverse effect on populations.

The use of river courses by hunters and anglers, especially if they have companion or hunting dogs, may also be an issue when the ducks are either breeding or moulting (a period in summer when the ducks lose their feathers to grow a new set - during which time they cannot fly).

Fight for survival

The blue duck is classified as a nationally vulnerable species, with current populations declining, and unless the causes for its decline are remedied (or reduced), the species faces a very real risk of becoming extinct.

A recent estimate, based on surveys and site records, provided a national figure of approximately 2500 individuals and declining. Blue ducks have been adversely affected by many human induced changes.

In particular:

The direct loss of suitable riverine habitats due to the clearance of vegetation from stream and river banks, water diversions, poor water quality and damming for hydro-electric and irrigation schemes;
Increased mortality caused by introduced predators and human disturbance. More recently, research has found that stoats are a major predator of blue ducks, and probable cause of population declines through decreased recruitment of juveniles.
Possums, cats and dogs are also threats to whio.

Unlike some endangered bird species, blue ducks cannot simply be transferred to off-shore islands to ensure their viability, because they rely on large areas of quality, fast flowing riverine habitat that is unavailable on islands. The continued survival of this species is therefore largely dependent on the protection of secure source populations throughout mainland New Zealand.