Spotting water vole droppings is a really important skill for surveyors, since it's probably the most unambiguous sign of the animal's presence. Latrines, eg photo 2, are often fairly easy as clumps of pellets tend to stand out (unless they've been well-trampled, in which case look for a small patch of soil that's differently-browner than its surroundings). But individual droppings are tricky to see against a bare bank. Can you see the poo in photos 3 and 4? Once you've spotted a place where water voles like to come and mark, then that's a good place to wait with your camera.