I heard somewhere recently that birds that specialize in feeding in trees, as opposed to ground feeders are finding it tough finding food to feed their young as well as themselves, due to heavy rain and flash flooding that is washing caterpillars straight out of the trees.
Seeing birds introducing their chicks to my feeding station, reminded me to restock with high protein feed fat-balls and meal worms
Any high energy food will help, feed the adults so they can give the insects all the insects. We have a pair of bluetits coming to our feeder on a seventh floor balcony.