Fecal sac

The nestling usually produces a fecal sac within seconds of being fed; if not, a waiting adult may prod around the youngster's cloaca to stimulate excretion.

[4] For example, nestling curve-billed thrashers raise their posteriors in the air, while young cactus wrens shake their bodies.

[10] Experiments on starling nests suggest that bacteria in faeces produce volatile chemicals that may provide cues for predators and ectoparasites such as flies in the genus Carnus.

[12] Even brood parasites such as brown-headed cowbirds, which do not care for their own offspring, have been documented swallowing the fecal sacs of nestlings of their host species.

Examination of the contents of the sac can reveal details of the nestling's diet,[14][15] and can indicate what contaminants the young bird has been exposed to.

The head and upper torso of a gray bird with a small white object in its beak protrudes from a hole in a tree trunk.
An oak titmouse removes a fecal sac – feces wrapped in a membrane – from its cavity nest.
A blue bird with a small white object in its beak flies against a green background.
Many species, such as the western bluebird , carry fecal sacs some distance from the nest.
An adult Eurasian blue tit collecting the fecal sac of a chick (just hatched, still naked and blind) to ensure the cleanliness of their nest.