Informative article right on the mark
It is also very interesting to note that as these chicks are fed, they consume all the moisture their bodies need from the food they eat, unlike our little backyard birds that drink from puddles and birdbaths. Mike had it right on about eating sleeping and pooping. They are growing so rapidly they have no energy for anything else for three or four weeks. The mother's duty is to feed them, protect them from the rain and the sun with her wings spread over the chicks, sometimes for hours at a time, sheltering them, and the father's duty is to bring home the fish.
Each species of bird have their own way of eating, sleeping and pooping. The robins poop once a day and it comes out as a gelatinous sack and the parent picks it up and dumps it. The ospreys, eagles, etc., raise their little bottoms and shoot it over the side of the nest. So the next time you see a nest, you now know where the poop went.