My brother is a videographer & has filmed some interesting nature footage. He just posted this video of the activity in a robin's nest in his backyard.
He was able to get nice closeup footage of the robins taking care of the nest & their baby birds through the foliage.
One thing that I didn't realize was that the baby birds create fecal sacs, which basically hold their excretions so the parents can remove them & keep the nest clean. Apparently, sometimes the adult birds eat these 'poop sacks' (as we've been calling them). You can see the adult pull one right out of the baby's butt, at about the 2:00 mark.
Despite the subjective grossness of some of it, the life cycles of animals are truly a wondrous phenomenon.