It took us a while the other evening to recognise what exactly was moving on the nut feeders located half way up the tree trunk. It was too late in the evening for a bird and getting quite dark so all birds should be safely tucked up for the night. Suddenly a little head popped out and then another and we realised we were now feeding wood mice as well as all the other wildlife of the forest. They are also known as 'long-tailed field mice' and, as we can verify, they are very agile climbers. They make their nests underground in complicated burrows or in holes in trees. It was quite amusing watching them chase each other round the feeder and then fall off into the bushes below. Wood mice are one of the most common European mammals.
Luckily the cats were asleep.