By Annie Hill
The original article in Russell Lights | Ngā Mārama o Kororāreka, March 2026 edition
It’s fair to say that weasels (mustela nivalis) drew the short straw when they were introduced to Aotearoa, New Zealand. The smallest mustelid in the country, they were brought here to help eradicate rabbits, which at up to 2 kg, are 13 times the weight of the largest weasel. They are certainly ferocious little animals and can kill a grown rabbit, but would much prefer voles, which are nonexistent here. Stoats, on the other hand, eat both larger rodents and rabbits, while ferrets are domesticated animals, bred from European polecats at least a couple of thousand years ago, specifically for hunting rabbits. In terms of their effect as predators, no doubt both have had some success, but not so weasels. Contrary to what The Wind in the Willows would have you believe, far from co-operating with weasels, stoats both compete with and prey on them. Rats also compete for food and resources, and weasels avoid them. All three mustelids were introduced in the late 1870s, at the demand of farmers and in spite of protests of bird experts; astonishingly, they were legally protected until 1936. It’s very fortunate that they were never freed on Rakiura Stewart Island or Aotea Great Barrier Island.
Weasels are only found in low numbers in Aotearoa New Zealand, probably because the country provides marginal habitat with no small mammals, apart from mice. In other countries, weasels will live in most habitats, as long as there’s plentiful prey and good cover; the relative abundance of mice in our gardens, farmland and scrub, probably explains their frequent presence in these areas.
Frequently mistaken for the considerably larger stoat, weasels have a long narrow body, short legs, a russet-brown back, and a creamy white throat and belly. They have a shorter tail than stoats, lacking the diagnostic black tip. Adult weasels are about 11 – 25cm long, the females much smaller than males. She usually weighs between 60 and 80g, while a male can weigh up to 150g: twice her weight. While stoats bound along, arching their backs as they go, weasels run with a similar pace – their hind feet landing in the same spot as their forefeet – but keep their back straight. They’re very fast and can reach speeds of up to 24 km per hour.
Weasels are quite vocal and when taken by surprise will give a guttural hiss. Both very fierce and dauntless, they stand up to much bigger animals, threatening them with short screaming barks and shrieks, wailing shrilly or squealing when they defend themselves. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while sub-dominant weasels will emit submissive squeals. However, non-aggressive communication between males and females, or a mother and her kits, takes the form of a high-pitched trilling.
Hunting both day and night, and with voracious appetites – they typically eat around one-third of their body weight daily – weasels catch their prey by running it down. In Aotearoa New Zealand, they generally eat mice and their long, slender body allows them to chase them through burrows and tunnels, giving them an advantage over larger predators. They often carry their victim back to their den, to cache it. (If we do manage to eliminate possums, mustelids, rats and feral cats, mice are likely to become a serious pest. Mercifully, weka, herons, owls and falcon all occasionally eat them.) When hunting, weasels rely on their keen sense of smell and hearing and lacking their chosen prey, will eat birds, their eggs, small reptiles, frogs and insects, including wētā. Studies of their diet show that they probably eat lizards more often than stoats do, so they’re probably a serious threat to our geckos and skinks. They’re reported to ‘dance’ like stoats, when hunting rabbits, which behaviour mesmerises the rabbit, allowing the weasel to get closer and closer, before leaping in for the kill. However, while only large males are likely to take on a rabbit, they all occasionally enter rabbit holes to hunt, probably hoping to find babies on their own.
Males and females generally live solitary lives, with the both scent-marking their territories and defending them vigorously. The male has a much larger range than do females and his territory may overlap or include several female territories. Weasels don’t dig their own tunnels, but nest in the abandoned burrow of other species, usually choosing one with a small entrance, measuring about 2.5cm across. They also den in hollow logs, rock crevices, and under tree roots.
Both males and females mate repeatedly with many partners during the breeding season, which lasts from September to March. The chosen burrow is modified to create a nest chamber, located up to 15 cm below ground. It measures about 10 cm in diameter, is lined with straw and the skins of the weasel’s prey and is used for sleeping and storing food, as well as for rearing kits. Females have up to two litters a year, (very rarely three) of three to six kits. Only the mother cares for the young, which are born pink, naked, blind and deaf, but gain a white coat of downy fur at the age of 4 days. At 2 to 3 weeks of age, they start to eat solid food, though lactation can last 12 weeks. Their eyes and ears open at around 3 weeks, and by the time they’re 8 weeks old, they can be going out with their mother, hunting in ‘gangs’. Kits reach sexual maturity at 3 to 4 months and weasels can live for 7 or 8 years.
In their native habitats, weasels are predated by barn owls, which have a growing resident population in Northland, and it’s possible that Kāhu Swamp Harrier would hunt the occasional one, but stoats are their main predator. No doubt cats will have a go at a weasel, but the latter is incredibly aggressive and would certainly stand up for itself. Your average pet moggy would probably back down. Evidence appears to show that weasel numbers will increase as stoats decrease, so we may be seeing more of these incredibly fast and agile hunters around. Because they’re cunning, intelligent animals and lightweight, they’re not very easy to trap with the normal stoat trap, which needs recalibrating for them; at present, they’re caught as ‘by catch’ by Predator Free Russell, rather than having traps set specifically for them.
