This year we had a pair of great tits nesting in our nest box, which has a camera in it - all went well and two chicks fledged on 19th May.
A week or so after the fledging, we noticed a great tit going into the used nest box; we looked at the feed from the camera and saw the bird sat on the nest - however, it didn't look like our mother great tit from the original family (she looked very sleek and had a very dark black cap whereas this one is a bit more scruffy and head not as dark). So we don't think it's the same bird. But since then the new bird has been going in and out of the box and spending a lot of time sat on the nest.
We thought that it might be a new female who is planning to breed (possibly a second brood), however after several weeks of the bird attending the nest we can't see any eggs, just a bit more nesting material has been added. It is still in and out of the nest and often sitting on it during the day. We haven't seen or heard a male around, whereas with the first family the male was very attentive.
We're not sure what's going on. Either it's the same original female and her appearance has changed, or it's a new bird who has taken a liking to the nest, or it's a chick from the original family returning to the nest for some reason... either way, what is it doing in there? We're stumped! If the bird was planning to use the nest to breed wouldn't there be eggs by now? And do great tits even breed in used nests?
We're also a bit worried that the bird might be ill and that's why it's spending time in the nest box.
If anyone can shed any light on this behaviour I'd be very interested to hear it! Thanks in advance :)