22 January 2021 update: sadly the parental activity at this nest seems to have stopped since at least 18th January when I began re-visiting. It's possible there's a chick/s inside and I'm having a very bad run of timing, but I have to say it isn't looking good... :-( Either that or there was a fledging event in my absence, but this nest seemed to be a little back in its progression... I'm just thinking aloud, the fact that the parents were calling to the chick on evening of 13th without going inside could suggest the chick/s were closer to fledging than I realised...???