
but once they got the hang of sitting on this they - or was it a s/he only - mastered hanging face down from it and peering into the entrance hole. S/he then chewed at the hole over some weeks to make it bigger and then climbed in after much contortion to use it as a bolt hole in wet weather. So, no blue tit occupants last summer.
The enlarged hole can be seen more clearly in the second picture.
So now I have changed the slope of the roof and added a metal cover to form a bird sized entrance 0f 25 mm. Unfortunately my carpentry was not too good and so I had to add a very squirrel friendly horizontal strip on top of the apex to make it weather tight. To reduce the "friendliness" I have put in some screws into the top piece and hopefully even the agile squirrels will not find this comfortable. Within an hour of putting the new box up a blue tit was investigating it. My fingers are crossed for the bird.