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

feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) 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 ...

of some species of nestling

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s. It allows parent birds to more easily remove fecal material from the

nest A nest is a structure built for certain animals to hold Egg (biology), 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 ...

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

cloaca A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilagin ...

to stimulate

excretion Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, Kidney (vertebrates), kidneys, and skin. This is in contrast with secretion, where the substa ...

. 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 thrashers raise their posteriors in the air, while young cactus wrens 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 generally have an anisodactyl arrangement of their ...

s and their near relatives, which have

altricial Precocial species in birds and mammals are those in which the young are relatively mature and mobile from the moment of birth or hatching. They are normally nidifugous, meaning that they leave the nest shortly after birth or hatching. Altricial ...

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 egg, 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''. 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 may refer to: Nature * Brood, a collective term for offspring * Brooding, the incubation of bird eggs by their parents * Bee brood, the young of a beehive * Individual broods of North American periodical cicadas: ** Brood X, the largest ...

s 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. 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 Diet may refer to: Food * Diet (nutrition), the sum of the food consumed by an organism or group * Dieting, the deliberate selection of food to control body weight or nutrient intake ** Diet food, foods that aid in creating a diet for weight loss ...

, and can indicate what

contaminant Contamination is the presence of a constituent, impurity, or some other undesirable element that renders something unsuitable, unfit or harmful for the physical body, natural environment, wiktionary:Workplace, workplace, etc. Types of contamina ...

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

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