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Meet the mustelid family

There are three members of the mustelid family residing in New Zealand, and none of them are welcome. Meet ferret, stoat and weasel. Badgers, minks and otters are also mustelids. They seem a bit cuter, but then they aren’t munching their way through our native bird populations.

All three species were bought to New Zealand from Europe in the 1880’s to control our plaguing rabbit population. There is no doubt they did prey on rabbits, as their numbers rapidly increased. Unfortunately, rabbits weren’t the only meal on their menu. Our native species, having evolved with only aerial predators, are na├»ve when it comes to these effective ground predators that use smell to hunt.

Sadly between the three, they have decimated many of our native bird, lizard and insect species.

So, who are they?


The largest mustelid in New Zealand is the ferret.

Ferrets, being somewhat hefty in stature, tend to remain on or close to the ground. They are also more common in open country such as wetlands, riverbeds, dunes which is unfortunately where our endangered bittern, black stilt, and various penguin species reside.

They are also a threat to kiwi living in fragmented forest patches and are big enough to kill an adult kiwi, which the other mustelid members are not able to do.


Stoats are next in size and have been touted as New Zealand’s public enemy number one.

They are one of the three target species for Predator Free 2050, along with rats and possums.

Stoats are implicated in the extinction of our native bush wren, laughing owl, and native thrush and as the major cause of decline of many others.

Along with rats, they caused the local extinction of Marlborough’s mohua population on Mt Stokes in 2001.

Unlike ferrets they are highly agile, climb trees and target eggs, chicks and incubating adults.

Stoats are the reason kiwi are declining at such a drastic rate. While adult kiwi are big enough to fend for themselves, stoats can easily sniff out and target kiwi chicks. As well as birds, stoats also enjoy a meal of lizards and insects.


Weasels are the smallest of the mustelid family, and are often confused as small stoats (check their tail: stoats have a black tip, while weasels are a uniform brown).

Their size doesn’t reduce their ferocity, but does reduce the size of the prey available to them. Having said that they are still able to make a meal of eggs and chicks in the nest, as well as lizards and invertebrates.

No one can deny mustelids are highly successful species and their survival abilities deserve some respect. However, our native species have existed for 55,000 years without mammalian predators. In the 150 to 250 years that most predators have been present in New Zealand, they have not been able to evolve strategies to cope with mammalian predators. They need our help and luckily advances in technology and science will enable conservation managers to increase the tools in our toolbox through new toxins, traps and lures. 

Written by Wendy Sullivan, DOC, for the Marlborough Express.
Images created by Nigel Hollyman, based on internet sources.