Hi Susan, they will look around different boxes to see which one they fancy and then build in there. Once they build the nest, they can be away all day only going back at night as she will lay an egg a day but not sit on them until all (upto 10) are laid, so they all hatch at the same time. It was only this morning that I noticed the blue tits take material into a box, quite excited as the box has been up years and never used. I put up a new great tit box and they were going in and out but have not seen any sign of material going in. Hope that yours come back.
Hi Susan l've had the same problem the blue tit was doing fine but would disappear for 2 days then come back to building the nest, then she slept there one night, but haven't seen her for about a week now, so feel she may have been frightened off by something, disapointing l know, my first time at cam nest box.
Thanks for getting in touch......great news, I've seen the male taking food into today... so I'm guessing the female is sitting pretty on her clutch....Well I hope so anyway...I will be upgrading my nesting box next year to include a camera!