Egg incubation

Incubation is the process by which certain oviparous (egg-laying) animals hatch their eggs; it also refers to the development of the embryo within the egg. Multiple and various factors are vital to the incubation of various species of animal. In many species of reptile for example, no fixed temperature is necessary, but the actual temperature determines the sex ratio of the offspring. In birds in contrast, the sex of offspring is genetically determined, but in many species a constant and particular temperature is necessary for successful incubation. Especially in poultry, the act of sitting on eggs to incubate them is called brooding.[1] The action or behavioral tendency to sit on a clutch of eggs is also called broodiness, and most egg-laying breeds of poultry have had this behavior selectively bred out of them to increase production.[1]

Female wild Mallard goes broody
A female Mallard duck incubates her eggs

Avian incubation

A wide range of incubation habits is displayed among birds. In warm-blooded species such as bird species generally, body heat from the brooding parent provides the constant temperature, though several groups, notably the megapodes, instead use heat generated from rotting vegetable material, effectively creating a giant compost heap while crab plovers make partial use of heat from the sun.[2] The Namaqua sandgrouse of the deserts of southern Africa, needing to keep its eggs cool during the heat of the day, stands over them drooping its wings to shade them. The humidity is also critical, because if the air is too dry the egg will lose too much water to the atmosphere, which can make hatching difficult or impossible. As incubation proceeds, an egg will normally become lighter, and the air space within the egg will normally become larger, owing to evaporation from the egg.

In the species that incubate, the work is divided differently between the sexes. Possibly the most common pattern is that the female does all the incubation, as in the Atlantic canary and the Indian robin, or most of it, as is typical of falcons. In some species, such as the whooping crane, the male and the female take turns incubating the egg. In others, such as the cassowaries, only the male incubates. The male mountain plover incubates the female's first clutch, but if she lays a second, she incubates it herself. In hoatzins, some birds (mostly males) help their parents incubate later broods.

The incubation period, the time from the start of uninterrupted incubation to the emergence of the young, varies from 11 days (some small passerines and the black-billed and yellow-billed cuckoos) to 85 days (the wandering albatross and the brown kiwi). In these latter, the incubation is interrupted; the longest uninterrupted period is 64 to 67 days in the emperor penguin. In general smaller birds tend to hatch faster, but there are exceptions, and cavity nesting birds tend to have longer incubation periods. It can be an energetically demanding process, with adult albatrosses losing as much as 83 g of body weight a day.[3] Megapode eggs take from 49 to 90 days depending on the mound and ambient temperature. Even in other birds, ambient temperatures can lead to variation in incubation period.[4] Normally the egg is incubated outside the body. However, in one recorded case, the egg incubation occurred entirely within a chicken. The chick hatched inside and emerged from its mother without the shell, leading to internal wounds that killed the mother hen.[5]

Embryo development remains suspended until the onset of incubation. The freshly laid eggs of domestic fowl, ostrich, and several other species can be stored for about two weeks when maintained under 5 C. Extended periods of suspension have been observed in some marine birds.[6] Some species begin incubation with the first egg, causing the young to hatch at different times; others begin after laying the second egg, so that the third chick will be smaller and more vulnerable to food shortages. Some start to incubate after the last egg of the clutch, causing the young to hatch simultaneously.[7]

Incubation periods for birds

Bird Incubation Period (days)
Chicken 21
Duck 28, Muscovy duck 35
Canary 13
Goose 28-33
Ostrich 42
Pheasant 24-26
Pigeons 16-19
Coturnix Quail 16–18
Bobwhite Quail 23-24
Swan 35
Turkey 28
Scarlet macaw 26

Mammalian incubation

Very few mammals lay eggs. In perhaps the best known example, the platypus, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally).[8] After laying her eggs, the female curls around them. The incubation period is divided into three phases. In the first phase, the embryo has no functional organs and relies on the yolk sac for sustenance. The yolk is absorbed by the developing young.[9] During the second phase, the digits develop. In the last phase, the egg tooth appears.[10] The only other egg-laying mammal is the echidna. New science research has been found that eggshells have a nanostructure that has inner and outer layers. The structure of this shell contains a protein known as osteopontin which is also found in tooth and bone. What reachers found was that the inner layers of the shell were thinner than the outer shells. This is because in the process of the egg being incubated the chicken embryos are taking the protein from the shell making the chicks skeleton stronger.

Reptilian incubation

Methods of incubation vary widely among the many different kinds of reptiles.

Various species of sea turtles bury their eggs on beaches under a layer of sand that provides both protection from predators and a constant temperature for the nest.

Snakes may lay eggs in communal burrows, where a large number of adults combine to keep the eggs warm.

Alligators and crocodiles either lay their eggs in mounds of decomposing vegetation or lay them in holes they dig in the ground.

Incubation by other vertebrates

Fish generally do not incubate their eggs. However, some species mouthbrood their eggs, not eating until they hatch.

Some amphibians brood their eggs. The female salamander Ensatina (Ensatina eschscholtzii) curls around the clutch of eggs and massages individual eggs with her pulsating throat.[11] Some aquatic frogs such as the Surinam toad (Pipa pipa) have pouches in their skin into which the eggs are inserted. Other neotropical frogs in the family Hemiphractidae also have pouches in which the eggs develop, in some species directly into juvenile frogs and in others into tadpoles that are later deposited in small water bodies to continue their development.[12] The male Darwin's frog carries the eggs around in his mouth until metamorphosis, and the female stomach-brooding frog of Australia swallows the eggs, which develop in her stomach.[13]

Incubation by invertebrates

Brooding occurs in some invertebrates when the fertilised eggs are retained inside or on the surface of the parent, usually the mother. This happens in some cnidarians (sea anemones and corals), a few chitons, some gastropod molluscs, some cephalopods, some bivalve molluscs, many arthropods, some entoproctans, some brachiopods, some bryozoans, and some starfish.[14]

See also


  1. ^ a b Ekarius, Carol (2007). Storey's Illustrated Guide to Poultry Breeds. 210 MAS MoCA Way, North Adams MA 01247: Storey Publishing. ISBN 978-1-58017-667-5.
  2. ^ De Marchi, G., Chiozzi, G., Fasola, M. 2008 Solar incubation cuts down parental care in a burrow nesting tropical shorebird, the crab plover Dromas ardeola. Journal of Avian Biology 39 (5):484–486
  3. ^ Warham, J. (1990) The Petrels - Their Ecology and Breeding Systems London:Academic Press.
  4. ^ Pettingill, OS Jr. Ornithology in Laboratory and field (4 ed.). Burgess Publishing Company. pp. 357–360.
  5. ^ 'Eggless' chick laid by hen in Sri Lanka, BBC News Online, 2012-04-19, retrieved 2012-04-28
  6. ^ Divoky, G.J.; Harter, B.B. (2010). "Supernormal delay in hatching, embryo cold tolerance, and egg-fostering in the Black Guillemot Cepphus grylle" (PDF). Marine Ornithology. 38: 7–10. Archived from the original (PDF) on 2012-03-21.
  7. ^ Wiebe, KL; Wiehn J; E Korpimaki (1998). "The onset of incubation in birds: can females control hatching patterns?" (PDF). Anim. Behav. 55: 1043–1052. doi:10.1006/anbe.1997.0660. Archived from the original (PDF) on 2011-07-28.
  8. ^ Erica Cromer (2004-04-14). "Monotreme Reproductive Biology and Behavior". Iowa State University. Archived from the original on 2009-03-13. Retrieved 2009-06-18.
  9. ^ "Ockhams Razor". The Puzzling Platypus. Archived from the original on April 4, 2005. Retrieved 2006-12-02.
  10. ^ Paul R. Manger; Leslie S. Hall; John D. Pettigrew (1998-07-29). "The development of the external features of the platypus (Ornithorhynchus anatinus)". Philosophical Transactions: Biological Sciences. The Royal Society. 353 (1372): 1115–1125. doi:10.1098/rstb.1998.0270. PMC 1692310. PMID 9720109.
  11. ^ Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press. p. 196. ISBN 978-0-691-03281-8.
  12. ^ Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press. p. 200. ISBN 978-0-691-03281-8.
  13. ^ Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press. pp. 202–204. ISBN 978-0-691-03281-8.
  14. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. pp. 62, 123, 297, 337, 364, 398, 811, 828, 887. ISBN 978-81-315-0104-7.

External links


An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. The two living species are the American alligator (A. mississippiensis) and the Chinese alligator (A. sinensis). Additionally, several extinct species of alligator are known from fossil remains. Alligators first appeared during the Oligocene epoch about 37 million years ago.The name "alligator" is probably an anglicized form of el lagarto, the Spanish term for "the lizard", which early Spanish explorers and settlers in Florida called the alligator. Later English spellings of the name included allagarta and alagarto.


Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small. Symptoms increase with the number of worms present and may include shortness of breath and fever in the beginning of the disease. These may be followed by symptoms of abdominal swelling, abdominal pain, and diarrhea. Children are most commonly affected, and in this age group the infection may also cause poor weight gain, malnutrition, and learning problems.Infection occurs by eating food or drink contaminated with Ascaris eggs from feces. The eggs hatch in the intestines, burrow through the gut wall, and migrate to the lungs via the blood. There they break into the alveoli and pass up the trachea, where they are coughed up and may be swallowed. The larvae then pass through the stomach for a second time into the intestine, where they become adult worms. It is a type of soil-transmitted helminthiasis and part of a group of diseases called helminthiases.Prevention is by improved sanitation, which includes improving access to toilets and proper disposal of feces. Handwashing with soap appears protective. In areas where more than 20% of the population is affected, treating everyone at regular intervals is recommended. Reoccurring infections are common. There is no vaccine. Treatments recommended by the World Health Organization are the medications albendazole, mebendazole, levamisole, or pyrantel pamoate. Other effective agents include tribendimidine and nitazoxanide.About 0.8 to 1.2 billion people globally have ascariasis, with the most heavily affected populations being in sub-Saharan Africa, Latin America, and Asia. This makes ascariasis the most common form of soil-transmitted helminthiasis. As of 2010 it caused about 2,700 deaths a year, down from 3,400 in 1990. Another type of Ascaris infects pigs. Ascariasis is classified as a neglected tropical disease.

Balut (food)

Balut ( bə-LOOT, BAH-loot; also spelled as balot) is a developing bird embryo (usually a duck) that is boiled and eaten from the shell. It originated from and is commonly sold as street food in the Philippines.

The Tagalog and Malay word balot means "wrapped". The length of incubation before the egg is cooked is a matter of local preference, but generally ranges between 14 and 21 days.

The eating of balut is controversial due to religious, animal welfare, and human health concerns.

Beaudouin's snake eagle

Beaudouin's snake eagle (Circaetus beaudouini) is a species of snake eagle in the Accipitridae family found in the Sahel region of west Africa. It forms a superspecies with the Palearctic short-toed snake eagle Circaetus gallicus and the black-chested snake eagle Circaetus pectoralis. This bird seems to be declining in numbers and the International Union for Conservation of Nature has rated it as a "vulnerable species".

Bird egg

Bird eggs are laid by the females and incubated for a time that varies according to the species; a single young hatches from each egg. Average clutch sizes range from one (as in condors) to about seventeen (the grey partridge). Clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized; it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs.

Bird eggs are a special kind of dinosaur egg.


The genus Brachylophus consists of four extant iguanid species native to the islands of Fiji and a giant extinct species from Tonga in the South West Pacific. One of the extant species, B. fasciatus, is also present on Tonga, where it has apparently been introduced by humans.


Broodiness is the action or behavioral tendency to sit on a clutch of eggs to incubate them, often requiring the non-expression of many other behaviors including feeding and drinking. Being broody has been defined as "Being in a state of readiness to brood eggs that is characterized by cessation of laying and by marked changes in behavior and physiology". Broody birds often pluck feathers from their chest and abdomen, using them to cover the eggs. As a consequence of this, they develop one or several patches of bare skin on the ventral surface. These reddish, well-vascularized areas of skin are usually called brood patches, and improve heat transfer to the eggs. Broodiness is usually associated with female birds, although males of some bird species become broody and some non-avian animals also show broodiness.


In biology, gonochorism (Greek offspring + disperse) or unisexualism or gonochory describes the state of having just one of at least two distinct sexes in any one individual organism. The term is most often used with animals, in which the individual organisms are often gonochorous. Gonochory is less common in plants. For example, in flowering plants, individual flowers may be hermaphroditic (i.e. with both stamens and ovaries) or gonochorous (unisexual), having either no stamens (i.e. no male parts) or no ovaries (i.e. no female parts). Among flowering plant species that have unisexual flowers, some also produce hermaphrodite flowers, and the three types occur in different arrangements on separate plants; species can be monoecious, dioecious, trioecious, polygamomonoecious, polygamodioecious, andromonoecious, or gynomonoecious.

Sex is most often genetically determined, but may be determined by other mechanisms. For example, alligators use temperature-dependent sex determination during egg incubation. Examples of gonochoric or dioecious pollination include hollies and kiwifruit. In these plants the male plant that supplies the pollen is referred to as the pollenizer.

Gonochorism stands in contrast to other reproductive strategies such as asexual reproduction and hermaphroditism. The sex of an individual may also change during its lifetime – this sequential hermaphroditism can for example be found in parrotfish and cockles.


Kleptothermy is any form of thermoregulation by which an animal shares in the metabolic thermogenesis of another animal. It may or may not be reciprocal, and occurs in both endotherms and ectotherms. Its most common form is huddling.

Lost Creek Lake

Lost Creek Lake is a reservoir located on the Rogue River in Jackson County, Oregon, United States. The lake is impounded by William L. Jess Dam which was constructed by the U.S. Army Corps of Engineers in 1977 for flood control and fisheries enhancement. The lake and dam were the first completed elements of the multi-purpose Rogue River Basin Project, consisting of Lost Creek Lake, Applegate Lake and the Elk Creek project. The lake is located approximately 27 miles (43 km) (straight line) northeast of Medford.

Lucilia mexicana

Lucilia mexicana is a species of green bottle blow fly of the family Calliphoridae. Its habitat range extends from southwestern North America to Brazil. L. mexicana is typically 6–9 mm in length with metallic blue-green coloring. This species is very similar in appearance to L. coeruleiviridis, the primary difference being that L. mexicana has two or more complete rows of post-ocular setae. L. mexicana has the potential to be forensically important in the stored-products and medicocriminal fields, but more research is needed for the fly to be used as evidence in criminal investigations.

Lucky Lake, Saskatchewan

Lucky Lake formerly known as Devil's Lake, is a village within the Rural Municipality of Canaan Rural Municipality No. 225, in the province of Saskatchewan, Canada. Lucky Lake had a population of 289 in the 2016 Canada Census, (a 0.7% increase from 287 in the 2011 Canada Census). The Village is located at the junction of Highway 42, Highway 45 and Highway 646 approximately 90 km north-east of Swift Current, Saskatchewan.

Mangrove finch

The mangrove finch (Camarhynchus heliobates) is a species of bird in the Darwin's finch group of the tanager family Thraupidae. It is endemic to the Galápagos Islands. It was found on the islands of Fernandina and Isabela, but recent surveys have failed to record the species on Fernandina. It has been classified as critically endangered by BirdLife International, with an estimated population of between 60 and 140 located in two large mangroves on Isabela. A study has shown that the two small populations remaining on Isabela Island have begun undergoing speciation and that one or both populations will eventually become extinct due to a lack of interbreeding.

Nassahegon State Forest

Nassahegon State Forest is a Connecticut state forest occupying 1,227 acres (497 ha) in the town of Burlington.The forest is managed for forestry and recreational purposes and is operated by the Connecticut Department of Energy and Environmental Protection.

Snares penguin

The Snares penguin (Eudyptes robustus), also known as the Snares crested penguin and the Snares Islands penguin, is a penguin from New Zealand. The species breeds on The Snares, a group of islands off the southern coast of the South Island. This is a medium-small, yellow-crested penguin, at a size of 50–70 cm (19.5–27.5 in) and a weight of 2.5–4 kg (5.5–8.8 lb). It has dark blue-black upperparts and white underparts. It has a bright yellow eyebrow-stripe which extends over the eye to form a drooping, bushy crest. It has bare pink skin at the base of its large red-brown bill.

This penguin nests in small (10 nests) to large (1200 nests) colonies under forest cover or the open. The main colonies are located on North East Island, other colonies are established on Broughton Island as well as the rocky Western Chain.

The Snares penguin's main prey is krill, supplemented by squid and small fish. The species is currently rated as vulnerable by the IUCN as its breeding range is restricted to one small island group. The current population is estimated at around 25,000 breeding pairs.


A stenotherm (from Greek στενός stenos "narrow" and θέρμη therme "heat") is a species or living organism only capable of living or surviving within a narrow temperature range.

The opposite is a eurytherm, an organism that can function at a wide range of different body temperatures.

Western banded snake eagle

The western banded snake eagle (Circaetus cinerascens) is a grey-brown African raptor with a short tail and a large head. Juveniles have paler and browner upper parts than adults, with white-edged feathers. Head, neck and breast are dark-streaked. The underparts are white with pale brown streaks, mainly on belly and thighs. Subadults may be all dark grey-brown without any streak on underparts. The eyes, ears, and legs are yellow. They have crested chests.

Birds (class: Aves)
Fossil birds
Human interaction


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