Fecal sac
Encyclopedia
A fecal sac is a mucous membrane, generally white or clear with a dark end, that surrounds the feces
of some species of nestling bird
s. It allows parent birds to more easily remove fecal material from the nest
. 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
. 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
s raise their posteriors in the air, while young Cactus Wren
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
s and their near relatives, which have 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
.
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. 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
s such as Brown-headed Cowbird
s, which do not care for their own offspring, have been documented swallowing the fecal sacs of nestlings of their host species
.
Studies have shown that avian polyomavirus
can be passed from offspring to parent birds through the removal of fecal sacs, particularly if the sacs are swallowed. Because females of many species remove more fecal sacs than do their mates, and because they are more likely to swallow those sacs when the nestlings are small, they are particularly susceptible to this method of disease transmission.
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
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.
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
of some species of nestling bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s. It allows parent birds to more easily remove fecal material from the nest
Bird nest
A bird nest is the spot in which a bird lays and incubates its eggs and raises its young. Although the term popularly refers to a specific structure made by the bird itself—such as the grassy cup nest of the American Robin or Eurasian Blackbird, or the elaborately woven hanging nest of the...
. The nestling usually produces a fecal sac within seconds of being fed; if not, a waiting adult may prod around the youngster's cloaca
Cloaca
In zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive, and urinary tracts of certain animal species...
to stimulate excretion
Excretion
Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism. 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 leaving the cell...
. 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
Curve-billed Thrasher
The Curve-billed Thrasher is a perching bird of the thrasher group native to the southwestern United States and much of Mexico....
s raise their posteriors in the air, while young Cactus Wren
Cactus Wren
The Cactus Wren is a species of wren that is native to the southwestern United States southwards to central Mexico.-Description:...
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
Passerine
A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...
s and their near relatives, which have 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
Fledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
.
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. 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 parasite
Brood parasites are organisms that use the strategy of brood parasitism, a kind of kleptoparasitism found among birds, fish or insects, involving the manipulation and use of host individuals either of the same or different species to raise the young of the brood-parasite...
s such as Brown-headed Cowbird
Brown-headed Cowbird
The Brown-headed Cowbird is a small brood parasitic icterid of temperate to subtropical North America. They are permanent residents in the southern parts of their range; northern birds migrate to the southern United States and Mexico in winter, returning to their summer habitat around March or...
s, which do not care for their own offspring, have been documented swallowing the fecal sacs of nestlings of their host species
Host (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
.
Studies have shown that avian polyomavirus
Polyomavirus
Polyomavirus is the sole genus of viruses within the family Polyomaviridæ. Murine polyomavirus was the first polyomavirus discovered by Ludwik Gross in 1953. Subsequently, many polyomaviruses have been found to infect birds and mammals...
can be passed from offspring to parent birds through the removal of fecal sacs, particularly if the sacs are swallowed. Because females of many species remove more fecal sacs than do their mates, and because they are more likely to swallow those sacs when the nestlings are small, they are particularly susceptible to this method of disease transmission.
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 (nutrition)
In nutrition, diet is the sum of food consumed by a person or other organism. Dietary habits are the habitual decisions an individual or culture makes when choosing what foods to eat. With the word diet, it is often implied the use of specific intake of nutrition for health or weight-management...
, and can indicate what contaminant
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...
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.