Nest recycling

Just a hint of movement in my peripheral vision suggest something had flown into the garage. Swallows nested in the roof beams last summer, so could it be the first swallow of the summer? On the first day of April?

Who am I fooling? When I went in to take a closer look the bird in question was up there among the beams, but of course it wasn't a swallow. It was a wren.

For wrens nest-building is a male chore and this particular cock wren has discovered last year's swallow nest and added his own touch, a roof of moss with a neat little entry hole. It  dawned on me that I had noticed bits of dry moss on the floor over the last few days, but hadn't thought to look up.

Now as far as I understand a male wren builds a number of nests around his territory and it's then down to the female to decide which one to use. Will she pick this customised swallow nest? 

And if she does, what happens when the swallows do turn up. It could be interesting.