Weasel – Mustela nivalis
Habitat: Urban & gardens, rivers and wetland, coniferous woodland, deciduous woodland, grassland, mixed woodland, arable land
Description: Fur ginger to russet brown, cream below, undulating border between. Long slender body, short tail (and no black tip). Slightly smaller than the stoat.
Size: Males 194-217mm; females 173-183mm. Tail: males 42-52mm; females 34-43mm.
Weight: Males 106-131g, females 55-69g.
Lifespan: Only around 10% survive to over 2 years old.
Origin & Distribution: Widespread throughout Britain, weasels are our smallest and probably most numerous carnivores. However, they are absent from Ireland and most off-shore islands. They are found in a wide range of habitats which include urban areas, lowland pasture, woodland, marshes and moors. Weasels are less common where their prey are scarce, such as at higher altitudes and in dense woodland with sparse ground cover.
Diet: Weasels specialise in hunting small rodents. The weasel’s small size enables it to search through tunnels and runways of mice and voles. Access to tunnels means weasels can hunt at any time of the day or year. They do not hibernate and can hunt even under deep snow. Additional prey such as birds, eggs and young rabbits may be taken, particularly if rodents are scarce.
General Ecology: Dens are usually nests of former prey taken over by weasels, and may contain the remains of food from several days meals. In colder climates in the north of Europe, the nests are often lined with fur from lemming prey. A weasel’s home range usually contains several dens and resting places that are visited at intervals. Weasel home ranges vary in size according to the distribution and density of prey. Male and females live in separate territories, male ranges being larger. Resident animals of both sexes may defend exclusive territories at times when numbers are high and neighbours numerous. In spring males extend their range to seek mates.
Breeding: Usually only one litter of 4-6 young are born per season, but two litters in years when field voles are abundant. Young are weaned at 3-4 weeks and can kill efficiently at 8 weeks; in a good vole year, young females can breed at 2-3 months old. Family groups split up at 9-12 weeks.
Conservation Status: Traditionally weasels have been considered enemies of gamebirds and gamekeepers have exercised intensive predator control, trapping and killing many weasels along with other carnivores. Weasels do kill some gamebird chicks, but probably very few. Weasels have no legal protection in Britain. Trapping probably has no long term effect: weasel populations are very resilient and they naturally suffer high mortality. In bad rodent years many weasels starve and few of the survivors breed. Local populations often experience extinctions. However, weasels are extremely good at recolonising abandoned areas when conditions improve.