Yvonne and I watch the arrival of Thomas, the blue tit, on the playback camera

You will, no doubt, have noticed that I've named the first bird to visit one of my four new nest boxes.  Perhaps I should have chosed a name like "Sydney", because I've known this to belong to both a boy and a girl and, of course, I haven't a clue whether my charming inhabitant is male or female.  I've also decided that it's a blue tit and not a great tit.  I did this by observing the patterning on the bird's head and checking which tit has a white circle as a crown in the book that the RSPB gave me when I joined the society a few week's ago.