Mustelids, ferrets stoats and weasels

(Mustela furo, Mustela erminea and Mustela nivalis vulgaris)
Containment Pests

(Mustela furo, Mustela erminea and Mustela nivalis vulgaris)

Containment Pests

Close up of a brown and white stoat.

Mustelids are a large group of small-to-medium-sized carnivores that originate from Europe. Three species of Mustelid, the Stoat (right), the Weasel and the Ferret, were introduced into New Zealand in the late 1880s to control rabbits. They will prey on birds, feral mice, rabbits, hares, rats, possums and insects. Ferrets have adapted so well to New Zealand that we now have the largest known population of feral Ferrets.

Reasons for the Strategy

Close up of a ferret in long grass.

All three Mustelids are active hunters and have a detrimental effect on our indigenous fauna. Ferrets (left) are also a recognised vector in the spread of the disease bovine tuberculosis to domestic livestock. Consequently, they pose a threat to the biodiversity values of the Tasman-Nelson region, and to the region’s pastoral industries.

Mustelids are assessed at “8” on the infestation curve. Given their widespread distribution, the best option is to promote the voluntary control of Stoats, Weasels and Ferrets. Assistance to land occupiers will include instruction in the field on control techniques. Extensive areas of suitable habitat, and the potential for them to cause significant adverse effects, mean the benefits of containment control far outweigh the costs.


To address the adverse effects of Mustelids - Stoats, Weasels (right) and Ferrets in the Tasman-Nelson region during the term of the Strategy.

Alternative Measures

Close up of a weasel eating a birds egg.

The principal alternative measure is to adopt a greater level of regional intervention, such as requiring land occupiers to control Stoats, Weasels and Ferrets. However, this option is considered inappropriate, given the widespread distribution of Stoats, Weasels and Ferrets, and the difficulty in controlling them.

Strategy Rule for Mustelids – Ferrets, Stoats and Weasels

The Management Agency will promote and encourage control.

Biosecurity Act Requirement

No person shall knowingly sell, propagate, breed, release, or commercially display Ferrets, Stoats or Weasels, under Sections 52 and 53 of the Act.

The Private Life of Stoats

These critters are not just a danger to birds - they have other nasty habits.

Stoats breed in litters of up to eight, and the females reach breeding age at 3-5 weeks. They leave the nest pregnant, but can delay implantation of their eggs for up to 9-10 months, until conditions are right, like a plentiful food supply following heavy beech tree seeding. These conditions lead to a boom in the mouse population and stoat numbers follow. Stoats range over a 60ha territory. They are cunning and difficult to trap - eggs and rabbit are among the baits the Delaware trappers find most successful. Fish is good too, but it also attracts wasps.