This is not my photograph but one borrowed from a Polish site to illustrate the worrying situation that has been mirrored this spring from my nestcam Great Tit's. They all succumbed by 17th May despite being fed intently by the parents for eleven days. Closer examination showed excess sunflower seeds filling their crops and little evidence of caterpillars being found by the parents. Perhaps the cold weather was to blame although seems like similar events are happening elsewhere too.
This highlights the critical importance of insects to food chains. Take away the insects and protection of many bird species is pretty much fruitless.