Walking through Linford Wood in Milton Keynes one lunchtime last week, I spotted this small burrow in the side of an irrigation ditch - the woods are maintained and there has recently been a major ditch clearance and coppicing initiative, which has revealed several of these holes, although this is the best example I've seen to date.
The hole is around 50-60mm in diameter, and in the first photo you can see the spoil from the dig falling away to the bottom of the ditch. The hole is around a foot, maybe slightly less, above the surface of the water and faces south-west, so gets a fair bit of light.
In the second picture, you can see the line of the ditch and the burrow's position therein. The whole area was previously under quite heavy undergrowth, brambles etc before the clean-up.
Normally there's not a great deal of water in these ditches, although this has increased a fair bit over the last week or so with all the rain we've had, I don't think the water level has reached the hole yet.
I hope all of the above preamble hasn't sent you to sleep - just tried to give as much info as possible!
Does anyone have an inkling of what might have made the burrow? Vole? Rat? Would be great to hear your ideas!