Baeolophus inornatus -San Luis Obispo, California, USA -nest-8

A fecal sac (also spelled faecal sac) is a mucous membrane, generally white or clear with a dark end, that surrounds the

feces Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a rela ...

of some species of

nestling Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight s ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s. It allows parent birds to more easily remove

fecal material Feces ( or faeces), known colloquially and in slang as poo and poop, are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relati ...

from the

nest A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...

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

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, ...

to stimulate

excretion Excretion is a process in which metabolic waste is eliminated from an organism. In vertebrates this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific tasks after ...

. Young birds of some species adopt specific postures or engage in specific behaviors to signal that they are producing fecal sacs. For example, nestling

curve-billed thrasher The curve-billed thrasher (''Toxostoma curvirostre'') is a medium-sized mimid native to most of Mexico and to the deserts of southwestern United States. It is a non-migratory species, and throughout most of its range it is the most common desert ...

s raise their posteriors in the air, while young

cactus wren The cactus wren (''Campylorhynchus brunneicapillus'') is a species of wren endemic to the deserts of the southwestern United States and northern and central Mexico. It is the state bird of Arizona, and the largest wren in the United States. ...

s shake their bodies. Other species deposit the sacs on the rim of the nest, where they are likely to be seen (and removed) by parent birds. Not all species generate fecal sacs. They are most prevalent in

passerine A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped'), which includes more than half of all bird species. Sometimes known as perching birds, passerines are distinguished from other orders of birds by th ...

s and their near relatives, which have

altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...

young that remain in the nest for longer periods. In some species, the fecal sacs of small nestlings are eaten by their parents. In other species, and when nestlings are older, sacs are typically taken some distance from the nest and discarded. Young birds generally stop producing fecal sacs shortly before they

fledge Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight. This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnera ...

. Removal of fecal material helps to improve nest sanitation, which in turn helps to increase the likelihood that nestlings will remain healthy. It also helps to reduce the chance that predators will see it or smell it and thereby find the nest. 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 In Greek mythology, Carnus (also spelled Carneus and Carneius) ( Ancient Greek: Κάρνος) was a seer from Acarnania, who was instructed in the art of divination by Apollo. According to the poet Praxilla, he was a son of Europa, who was brought ...

''. There is evidence that parent birds of some species gain a nutritional benefit from eating the fecal sacs; studies have shown that females – which tend to be more nutritionally stressed than their mates – are far more likely to consume sacs than are males. Even

brood parasite Brood parasites are animals that rely on others to raise their young. The strategy appears among birds, insects and fish. The brood parasite manipulates a host, either of the same or of another species, to raise its young as if it were it ...

s such as

brown-headed cowbird The brown-headed cowbird (''Molothrus ater'') is a small, obligate brood parasitic icterid native to temperate and subtropical North America. It is a permanent resident in the southern parts of its range; northern birds migrate to the southern ...

s, which do not care for their own offspring, have been documented swallowing the fecal sacs of nestlings of their host species. Scientists can use fecal sacs to learn a number of things about individual birds. Examination of the contents of the sac can reveal details of the nestling's diet, and can indicate what

contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that spoils, corrupts, infects, makes unfit, or makes inferior a material, physical body, natural environment, workplace, etc. Types of contamination Wi ...

s the young bird has been exposed to. The presence of an adult bird carrying a fecal sac is used in bird censuses as an indication of breeding.

References

External links

{{DEFAULTSORT:Fecal Sac Birds