Holly Faulkner, Project Assistant says:

Hi Catherine, making noise is instinct – just as a human baby cries when its needs are unmet. Birds normally chirp when they’re hungry – it’s a way of saying “hey! bring food over here!” Given that baby birds need to eat constantly – often every 10-20 minutes, there’s little time spent being quiet. There are also some reports of birds making noises to deter predators. Our sister project, NestWatch, heard from a participant about young Northern Flicker nestlings making a sound that was very similar to bees buzzing. One (untested) hypothesis is that this sound may deter predators that would otherwise prey on the nestlings. In any case, as the young get older and fledge the nest, they tend to quiet down, though you may still hear recently-fledged young begging parents for food as they follow them around for the next several weeks, learning how to fly and become independent.