by Steve Westerman

Wharfedale Naturalists Society

ALTHOUGH mild - it was a grey and drizzly day. I was walking alongside a small wooded area, where the ground under the trees was covered in the wet, orange and russet leaves of autumn. A rapid movement there caught my eye. It was only a brief glimpse – but it looked like a weasel (Mustela nivalis). I found a different vantage point – downwind and with a little cover – and waited for a while. Quite soon, the weasel reappeared and began to scour the area for prey. They are forensic in their approach. The weasel stayed within a fairly constrained area of perhaps 20 square yards. It would search intensely under some fallen leaves and twigs, and perhaps briefly dig in the earth below, before darting to another spot and repeating the process, again and again.

Suddenly, so quickly that I struggled to follow what was happening, it had scared a mouse into the open and the chase was on. The mouse lost. When the weasel came to a brief stop, the mouse was inert, either resigned or dead, and held by the top of its head in the weasel’s jaws. The weasel then bounded off to secrete its prize somewhere. It isn’t uncommon for weasels to cache food for later consumption. Immediately it was hunting again. The diet of weasels mainly comprises small rodents – particularly voles, but they will also take rabbits, birds, and eggs.

Weasels are the smallest member of the Mustelid family, that also includes (among others) stoats, badgers, and otters. Stoats are similar in appearance, although larger than a weasel. In isolation, the two species can most easily be differentiated by the black tip to the stoat’s longer tail.

In a previous Nature Notes (on Crayfish) I mentioned the problems that can be caused by the introduction of non-native species. Stoats and Weasels were introduced to New Zealand in the 19th Century, in the hope of controlling rabbits (an animal that had itself been introduced). Stoats thrived but, in addition to predating rabbits, they decimated the populations of many native birds that hadn’t evolved to cope with such a ferocious and skilled predator. Similarly, in the UK another introduced member of the Mustelid family, the American Mink, is causing problems. Originally captive in fur farms, for several decades there has been a wild population that are widely viewed as undesirable because of their effects on other wildlife, particularly water voles.