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Updated 7 June 2018 11:56am

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Why are mustelids a problem?

Mustelids (weasels, stoats and ferrets) pose a serious threat to our native animals and New Zealand’s farming industry. Mustelids kill native birds, with flightless and hole and ground nesting birds most at risk of predation. Mustelids eat birds, eggs and their young, and target native lizards and invertebrates like skinks and wetas. Mustelids also threaten domestic animals such as chickens, guinea pigs and rabbits.

Wild ferrets are a known carrier of Bovine Tb, a disease which threatens our domestic cattle and deer herds.

Description and background

There are three members of the mustelid family in New Zealand.


  • Weasels (Mustela nivalis) are the smallest of the mustelids, 20-25 cm long, deep brown to light tan coloured, with a light coloured underbelly and throat. They have a short tapering tail, which is all brown.
  • Stoats (Mustela erminea) are the most common in the Wellington region. 35-40 cm long, brown/black colouring with a pale belly and throat and a bushy black-tipped tail.
  • Ferrets (Mustela furo) are the largest, measuring from 48 – 55 cm long. Creamy yellow coat with long black guard hairs. Tail and legs are darker than the body, with a dark ‘bandit’ mask around the eyes and nose.

Mustelid droppings are long and thin and strongly scented, often with a twist at each end. The scats are usually left in prominent places such as the middle of tracks or clearings. Mustelids may leave dead prey with chew marks on their head or neck, but usually only abandon their catch if they are disturbed.

All of the mustelid species were introduced into New Zealand in the 19th Century in an attempt to control the rabbit population. The potential impact on the native bird species was known, but agriculture took precedence over the environment at the time. Ironically the rabbit problem is now largely under control, while mustelids remain a key threat to many of our most endangered bird species.

What can I do?


Mustelids are difficult animals to control. As a roaming predator, they have a territory of over a kilometre. They are highly mobile and inquisitive, and are attracted to areas with available prey. Areas with high rabbit or rat numbers will often attract mustelids, as will domestic animals such as chickens or waterfowl. Mustelids like to stay close to cover, and will often travel along tracks, walkways, fence lines, waterways and bush edges.

There are a range of traps available for mustelid control; with the most advanced being the DOC trapping series of kill traps. The DOC 200 will target weasels, stoats and rats, while the larger 250 will also kill ferrets. These traps can be purchased from Greater Wellington.

DOC has produced a few easy to follow, step by step videos on how to install, set up and service a DOC 200 trap.

Additional information can be found at –

NPCA Best Practice Guidelines

Predator traps website