Britain’s smallest carnivore, the weasel’s secretive habits mean it is rarely seen – cat
kills or road casualties, the occasional glimpse of this sinuous animal darting
across a road – and hence it is rarely recorded. The weasel is chestnut brown with a yellow/white belly, it has a short brown tail which lacks the black tip of its close relative the stoat. Male weasels can reach a total
length of 300 mm and weigh as much as 195 g, whilst an adult female may be only 200 mm long and half this weight: at one time the female was thought to be a separate species. A large male weasel and a small stoat may be similar sizes but the stoat always has a black tip to its tail. The stoat’s tail is also longer in proportion to its body and the margin between the dark coat and pale belly fur on the stoat is straight, whilst in the weasel it is irregular.
Droppings, or scats, are 3 to 6 mm long and 2 to 3 mm wide and contain hair, feathers and pieces of bone. They are coiled, similar in shape to that of the stoat but more twisted and curled. Weasels often make dens in the nests of their prey, sometimes lining them with fur from the previous residents.
The male weasel in the picture was brought in by a cat and left for dead. When it was seen to still be breathing, it was wrapped in a piece of towel and placed in a flower pot. Twenty minutes later it had recovered sufficiently to rear back and hiss loudly before scampering off into the
undergrowth. However, it did present an opportunity to take some useful
© David Groves
Weasels are found in a wide range of habitats, wherever there is sufficient food and
cover. They are not common in urban situations, or in dense commercial woodland
with limited ground cover. Male weasels aggressively defend territories of between
10 and 30 ha, depending on the prey availability and the type of habitat. A male’s
territory will overlap with several smaller female territories. Weasels are active
throughout the day, hunting for their main prey of small rodents by sight, sound, and
smell. Occasionally the weasel may stand on its hind legs to view and smell its
surroundings before dashing off again. Prey is killed by a bite to the back of the neck
and it may be dragged back to the weasel’s nest and stored. Weasels may kill over
10% of local rodent populations in a month. They also eat birds, and their eggs, and
larger males may also take young rabbits and rats. Weasel populations are closely
linked to prey numbers: when vole numbers increase the weasel may produce a litter
of up to 8 kits in April/May and then again in July/August. The female makes a nest
in an old rodent burrow or similar space and lines it with fur from her prey. The kits
are born 34 to 37 days after mating and weaned 4 weeks later. They leave the nest at
2 months and may live up to 3 years in the wild, although only 10% make it to 2 years.
The male takes no part in bringing up his family.
Foxes and domestic cats, owls and other raptors, and occasionally stoats, will all kill
weasels. Traps set for larger predators will also catch weasels, although they have little impact on game birds or domestic animals, and many are killed by cars as they hunt along roadside verges. When rodent numbers are low many weasels will starve and local populations can disappear completely. Weasels are host to a number of specific parasites which can affect their condition including the louse Trichodectes mustelae
and the nematode Skrjabingylus nasicola.
© Jenny Hobday
Weasels are widespread across Cornwall but thought to be under-recorded. There are no records from the Isles of Scilly. They occur throughout Britain, but not in Ireland. Weasels occur across Europe, Asia and NW Africa and have been introduced to Australia and New Zealand. The least weasel of North America is regarded as a sub-species of the weasel.
Did you know?:
Weasels need to eat one third of their body weight every day to survive. Unlike many other mustelids, weasels do not have delayed implantation as they are adapted to have as many young as
possible when food supplies are plentiful.
No specific methods. Footprint traps and camera traps may provide some data. Most records from incidental sightings, cat kills and road casualties.
Although not specifically protected in the UK, numbers are thought to be declining as a result of habitat degradation and secondary poisoning from rodenticides. Listed under Appendix III of the Bern Convention and identified as a Species of Conservation Concern under the UK BAP.