Many nestlings produce faeces that are surrounded by a membrane. These so-called faecal sacs are white with a dark, pointy end. Nestlings signal to their parents that they are about to defecate, e.g. by lifting their bottom. This allows a parent to pick up the sac straight from a nestling’s butt and remove it to keep the nest clean. Nestlings usually produce a faecal sac immediately after being fed, but if they fail to do so, the parents peck their bottom to encourage defecation. Parents sometimes eat the faecal sacs instead of removing them. Nestlings stop producing sacs when they leave the nest.