A narrow blur of warm brown flashes across the road ahead of me. Low to the ground, like a vole that has been elongated, this tiny, cylindrical mass of energy is a Weasel. In an instant it is gone, a bounding leap takes it up into the verge and out of sight. This is typical of an encounter with our smallest carnivore, all too brief and wholly unsatisfactory. On those few occasions when I have come across dead Weasels, freshly killed by passing traffic, I have been surprised at just how small they are. Even the largest males only just reach 24 cm in length and weigh in at less than 200 g. More typically, the males weigh in at 125 g and the females 70 g.
The Weasel is to be found across most of England, Wales and Scotland but is missing from nearly all of our offshore islands and, importantly, Ireland. It does best where there are good numbers of its favoured small mammal prey (mice and voles) and is usually associated with the cover provided by hedgerows and old stone walls. Its small size, which opens it up to predation by larger predators, may be one reason why it tends to avoid more open habitats.
At this time of the year the males are extending their exclusive territories, presumably in an attempt to increase access to potential mates, which will result in a number of female territories being enclosed within the male’s wider range. Individual Weasels do not make their own dens but instead occupy those of other species (such as rats, mice and moles). The small body size is an adaptation, allowing the Weasel to hunt and pursue small mammal prey down into their tunnel systems. This small size also enables them to enter and raid bird boxes in times when small mammals are less abundant. They have also been reported to take young Rabbits (a not uncommon prey item for the larger males when young Rabbits are available), reptiles, amphibians and even earthworms.