I found out a couple of things about my one-eyed vole tonight: firstly, I'm guessing she is female as I saw her topping up a large latrine. Males do make latrines, but not so many and only small ones.
And secondly, she is queen of the castle. She ran off another two-eyed vole with ease, and the intruder was almost deferential.
A total of four water voles appeared during this session.