Last year i put a new bird box up on the house in the back garden and this year it has been used by 2 blue tits. Me and the wife had been watching them going in and out feeding their young but 2 days ago next doors cat killed one of the parents. After that the other adult went back to the box a few times then for some reason wouldn't go in, it just sat on the roof of the box chirping . All day today there was no sign of the adult blue tit so i got my ladders and had a peek, to my sadness there was to dead chicks. Its a shame as they had all there feathers. Cats really annoy me sometimes, i know its instinct but the cat just killed the adult and left it.