The field vole problem

On Sunday the vole group went to a local farm where the landowners have fenced off an area of marshy field, with the specific aim of helping wildlife. We need more farmers like this! Fencing off the ground stops cattle from destroying banks and vegetation. It's especially useful along ths margins of ponds, streams and rivers. In this particular strip there's a large section of glyceria reed (top photo) which water voles love.

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As soon as we began to look for field signs, we found them: latrines, feeding stations and trackways were every few yards, plus a few burrows. However, we did run into a problem we hadn't anticipated last year, that of the similarity of field vole signs to those of water voles. Field voles also cut grass etc at a 45 degree angle; they also make little piles of chopped vegetation; they also form trackways through the grass. In the picture above, it's a water vole feeding station on the left, and a field vole one on the right.
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Not always easy to tell them apart, but there are some indicators. Firstly, water vole stuff tends to be on a slightly larger scale. Their trackways are more rat-sized, as opposed to mouse-sized, they chop their food into slightly longer pieces, and their droppings are bigger and darker. Secondly, water voles tend not to put droppings on top of their food piles. (Why would field voles do this??? But they do. Teeny green ones.) And thirdly, the location's a bit of an indicator. A trackway leading straight into the water is going to be water vole.