Update.
After dad left, mum disappeared too. We kept a sharp eye out for her, but she was nowhere to be seen.
After much umm-ing and ahh-ing, we sought advice from a few sources and the crux of it was, that if she didn't return (and we had weeks of seeing the parents return regularly, in fact, to think about them was to magically make them appear - it was that frequent) that we should open up the nest box to see what was what. We were assured that if the parents were to return, they would enter the box, regardless as to whether human hands had touched it or not.
I spent the entire day watching out for mum as I was that worried. I had a chair set up in full view of the nest box (I could see the box easily without bothering any other birds in the garden so it wasn't me that kept them away) but my vigil was fruitless, she didn't return, so after some more watching and no re-appearance, my husband investigated .. sadly the babies had all died. They were unfeathered, eyes closed, tiny things really. There were mites in there too. We sought further advice and were told to remove the nest and thoroughly wash out the box and let it dry. The babies were buried with their nest .. we had come so far with this nesting pair and took much delight in hearing the babies twittering whenever we went into the garden, that this felt the right thing to do. We cleaned out the nest box and felt incredibly saddened. One person that advised us, voiced an opinion that the female may have been just a youngster herself and didn't realise her babies had died which was why she kept returning even after they had died .. she was waiting for them to lift their heads and thinking about it, I'm sure this was why the male left .. he looked a little rough around the edges, we're sure he had more experience and had left as he knew they weren't going to lift their heads, unlike poor little Mum.
We saw nothing of either parents for the rest of that day ..
Anyway,the next day, I was woken by the familiar twittering of mum on the fence by the nestbox .. it literally broke my heart. I have no idea where she had gone .. just a feeling that she must have had some inkling that something was amiss, so was disappearing.
I spent the day crying my eyes out. She spent a good couple of minutes there calling, it was just terrible. She then went to have something to eat from the table .. then came back later.
We returned the nest box when it was dry and next morning she was back, peeked inside, then went to feed again.
She still feeds in our garden and has the chance glance inside the box, almost out of habit .. it's terribly sad. I've had to remind myself that her babies had died, they had mites, to let her keep returning to a mite ridden nest box of sadly deceased chicks would have done her no good at all.
So, not a good start to our nesting bird experiences
