Dead blue tit chicks

[FredFlintstone100]

Almost all of the chicks in our bird box have died. We watched a couple fledge yesterday but the parents continued to return to the box with food for the remainder of the day. All quiet this morning but, on closer inspection, it turned out there were 5 dead chicks in the box, one of which looked ready to fledge but the rest were less developed.
Do blue tits kill each other’s young? Maybe something else attacked them. Box is north facing. No problems in previous years. Weird.

poison? Is sad.

Maybe someone is spraying weedkiller or putting slug pellets down. How sad. There are so few small birds around.

Oh that is really strange, and so sad. Heat ? Lack of food ? You could get them out and check for injury, but if something had attacked them it would have eaten them. Not left them in the box. Try tweeting Springwatch, they might have some advice.