So let's take a closer look at our visitor.
As well as a largish white back patch, he seems to have flecks of white over much of his back.
Here he is taking a good look round. It must be a bit scary going into a new box for the first time - what would happen if Neptune or Fantail paid a visit?
Is someone coming?
What's all this rubbish doing here?
The visitor had a good look at everything, including the nesting material that Fantail had brought in.
His back looks most unusual. The white back patch seems to spread down towards his tail with speckles of white occurring some way down. Is this an old bird or just an unusual one?
Suddenly, he hopped up to the entrance hole and looked out.
Then he was gone. He was in the box for less than a minute. Let's hope he's decided that it's occupied and does not come back!