https://www.youtube.com/user/sinharat...
Once hatched, blue tit chicks spend around three weeks in the nest before fledging. During that time they more than quadruple in size, developing feathers and the wing muscles they will need for survival outside the nest. Feeding a nest full of voracious chicks is a full-time job for both parents

Feeding chicks takes its toll on the parents as they flit in and out of the nest box with juicy fat caterpillars. Each chick can eat 100 caterpillars a day, so to feed a brood of ten, adults need to find as many as 1,000 caterpillars a day.