We were sat in the garden about six o'clock and suddenly it got very noisy. We have a large silver birch tree and maybe 30 blue tits all flew into it a few at a time. It was like all the parents who normally live in our garden in the winter but had left to breed, returned all at once with their young. The tree was alive. Then suddenly it went quiet. Don't where all the blue tits went because we didn't see many leave.