Hi Folks, Perhaps some others of you have heard of this before and could possibly explain what could have happened. This week after the brood of blue tits had left the nestbox, I decided to take the box down to clean it out and fumigate it.I noticed that it was much bigger this year than other years.When I took the old nest to my compost heap and started to break it up,I found that the top nest had been built over another nest with seven eggs in it. Is it possible that the original nest had been built too early and the very cold weather we had in April could have made the eggs infertile and the pair off blue tits realised this and subsequently built another nest over the top of the original one, or is it possible that another pair moved in and built their own nest. Would be interested to know if anyone knows the answer. Many thanks. Alan Pearce.