Above: young adult vole. Below, an older one.
Can you tell individual water voles apart? I'm sometimes asked. The answer's no, unless they have a particular scar, but you can tell young voles from old even if they're the same size. The fur on this adult at the top is lovely, glossy and spruce, while the fur on this older adult is scruffier and there's some hair loss (mange?) around the eye.