by Steve Westerman

Wharfedale Naturalists Society

FOLLOWING last week’s Nature Notes (31st December 2020) in which I described seeing an American Mink on the bank of the river Wharfe, I thought I would continue the theme and focus on two other Mustelids that aren’t usually associated with the river but can (at least occasionally) be found there.

Stoats and Weasels are small carnivores. Differentiating them can be tricky because it can be difficult to get a good view. However, Stoats are larger than Weasels and, more tellingly, have a relatively longer tail with a black/dark tip (see photograph).

Like Mink, both species are generalist predators that will take a variety of mammals and birds. However, in keeping with their size difference, they have different preferred prey species. For Stoats (especially males) rabbits form the largest part of their diet (when they are available). In contrast, small rodents (voles and mice) form the largest component of the diet of Weasels.

Following a prolonged dry spell, a few years ago, the river level was particularly low. My attention was drawn to a rising swell of bird alarm calls coming from what should have been an island in the river. However, with the prevailing dry conditions it was easily accessible from the far bank. I wasn’t well positioned to see what was going on, but after a while I spotted a Stoat, making its way along the river bank, searching for prey. Eventually it reached the ‘island’. Any eggs or young birds weren’t likely to last long. The alarm calls continued ….

Much more recently I watched a weasel hunting along a steep river bank. At a distance it was difficult to see. There was just the occasional flash of the pale fur of its throat and underside as it darted in and out of thick vegetative cover. This is a place that normally provides sanctuary for various birds (including wrens, blackbirds, robins, and sometimes even a kingfisher). It offered no refuge on this day! At one point the Weasel’s attention seemed to be drawn by something on the other side of the river and it started looking for a way to cross. Stoats and Weasels are capable swimmers (although not to the extent of Mink or Otters). However, on this occasion the Weasel didn’t seem too confident. The level of the river was particularly high and the water was fast flowing. After weighing its options for a while, it stopped short of launching itself into the water.