In reply to chris_s: Oh right, I thought it was the area I was in a few weeks back - Sgurr nan Ceathreamhnan area - all the hill sides were covered in runnels where they have been living under the snow, and there were mice everywhere. While I was packing my tent away, they were running underneath the groundsheet and hiding. I even took a video, they were quite tame.
I have no idea why they would be so prevalent. Let's hope they eat all the ticks!