Treecreeper - there are a pair of these, one often feeding the other.
Below, water vole droppings on mud can be hard to spot!
Spotting water vole droppings is great because they're one of the few field signs that are unambiguous. Rounded at each end, slightly larger than Tic Tacs and odourless, water vole pellets are often deposited as territorial markers. Sometimes voles will choose prominent, impervious surfaces on which to poo, like logs or flat stones or plastic bottles, old car sponges, abandoned polystyrene tiles. Then latrines are easy to spot. But when voles leave their olive/brown droppings on mud - and then trample them - it can be hard to distinguish. Use a zoom lens or binoculars to examine closely any spot where the soil looks a bit lumpy, or where flies are gathering.