Play this audio clip
Can anyone identify the bird song in this clip? There is a robin singing in the foreground but there is a second bird which I cannot identify. You can hear it clearly around 15 seconds and 21 seconds. It seems to be a 6 note repetitive call. This was recorded in mid February in my London back garden next to a park. Any ideas would be appreciated!
That could be a Dunnock?
Unicum arbustum haud alit duos erithacos
(One bush does not shelter two Robins)
Zenodotus (3rd Century B.C.)