They were introduced to New Zealand in the late 1800s to try to control a plague of introduced rabbits. Tragically for New Zealand’s flightless ground nesting birds, lizards and insects, they proved much easier to catch than rabbits.
Stoats are a particularly effective predator, able to kill kiwi chicks that weigh four or five times more than they do. Highly mobile and wily, stoats are notoriously difficult to trap.
Older kiwi, with their feisty nature, sharp claws and strong legs, are better able defend themselves. However, they are vulnerable to ferrets, the largest of the mustelids. In Northland, over three months, a single male ferret killed 3 out of 10 breeding male kiwi and destroyed two other nests.
While little is currently known about the impact of weasels, the smallest of the mustelids, many experts believe that they could kill kiwi chicks in the first few months of life.
Mustelids are effective predators, kill wantonly and are very mobile. A male stoat in Trounson Kauri Park, Northland, was radio tracked over a range of 208 hectares.
While they are widespread on mainland New Zealand, mustelids are not found on many offshore island sanctuaries, including Stewart Island, the home of the Stewart Island tokoeka.
Know your mustelid
Also known as fitch or polecat, are about the size of a small cat. They are usually brown or black with creamy underfur and a darker mask across the eyes.
They hunt mainly at night and prefer open areas and bush edges. They eat small animals, such as rabbits, rodents, lizards and frogs.
Stoats are the mid-sized mustelid and the most abundant and widespread in New Zealand.
They are light brown with a white belly and have a long black-tipped tail. Stoats are active during the day, and especially good climbers and swimmers.
They are opportunists and will eat anything – rodents, birds, weta, lizards and kiwi chicks. They kill more than 50% of all chicks that hatch in areas where the stoats are not being controlled.
These are the smallest mustelid, light brown, with a short half-tail and patchy white belly.
They are found in low numbers in most habitat types.
Weasels will tackle prey much larger than themselves and nesting birds are easy targets, as are lizards and insects.
Much work to protect kiwi involves trapping or poisoning mustelids. The Kiwis for kiwi How to Save Kiwi Videos have a lot of information on how to control and monitor these predators.