Nest sanitation is important when raising chicks, so rather than defecate in the nest, young birds produce a packet of waste called a fecal sac. Some parents carry this sac away from the nest before disposing of it; others simply eat it. Young birds have highly inefficient digestive systems, and the fecal sac still contains valuable nutrients for the parents.
This video accompanies Chapter 11, Breeding Biology of Birds, Handbook of Bird Biology, 3rd Edition from the Cornell Lab of Ornithology and Wiley Publishing.
Recorded by David A McCartt, Macaulay Library