we have a great tit which keeps knocking its beak on two small windows
in the attic and appears to be desperate to get inside.

[snip]

Is it tapping the window, the putty around the window or the wall around the
window? I've problems with birds stealing putty and the local sparrows are
pecking bits out of some rendering below a patio door. Either they are a
very patient crack thieving team trying to get in or there is some sort of
minerals that they get out of this.

Paul DS