Avian incubation

Avian incubation

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Incubation refers to the process by which certain oviparous
Oviparity
Oviparous animals are animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, reptiles, all birds, the monotremes, and most insects, some molluscs and arachnids....

 (egg-laying) animals hatch their eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

, and to the development of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 within the egg. The most vital factor of incubation is the constant temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 required for its development over a specific period. Especially in domestic fowl
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...

, the act of sitting on eggs to incubate them is called brooding. The action or behavioral tendency to sit on a clutch of eggs is also called broody, and most egg
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

-laying breeds of poultry
Poultry
Poultry are domesticated birds kept by humans for the purpose of producing eggs, meat, and/or feathers. These most typically are members of the superorder Galloanserae , especially the order Galliformes and the family Anatidae , commonly known as "waterfowl"...

 have had this behavior selectively bred
Selective breeding
Selective breeding is the process of breeding plants and animals for particular genetic traits. Typically, strains that are selectively bred are domesticated, and the breeding is sometimes done by a professional breeder. Bred animals are known as breeds, while bred plants are known as varieties,...

 out of them to increase production.

Avian incubation


The widest range of incubation habits is displayed among birds. In warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...

 species such as 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...

 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 Plover
Crab Plover
The Crab-plover or Crab Plover is a bird related to the waders, but sufficiently distinctive to merit its own family Dromadidae. Its relationship within the Charadriiformes is unclear, some have considered it to be closely related to the thick-knees, or the pratincoles, while others have...

s make partial use of heat from the sun. The Namaqua Sandgrouse
Namaqua Sandgrouse
The Namaqua Sandgrouse is a species of bird in the Pteroclididae family.It is found in Angola, Botswana, Lesotho, Namibia, South Africa, and Zimbabwe.-References:* BirdLife International 2004. . Downloaded on 24 July 2007....

 of the deserts of southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

, 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, and 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 Coscoroba Swan
Coscoroba Swan
The Coscoroba Swan is a species of waterfowl inhabiting southern South America. It is the smallest of the birds called "swans", but still a large species of waterfowl, averaging 4.2 kg , 1 m long and 1.57 m across the wings...

 and the Indian Robin
Indian Robin
The Indian Robin The Indian Robin The Indian Robin (Saxicoloides fulicatusRasmussen & Anderton emend the species epithet from fulicata to fulicatus since Saxicola is masculine and the -oides ending is always masculine according to ICZN Code 30.1.4.4....

, or most of it, as is typical of falcon
Falcon
A falcon is any species of raptor in the genus Falco. The genus contains 37 species, widely distributed throughout Europe, Asia, and North America....

s. In some species, such as the Whooping Crane
Whooping Crane
The whooping crane , the tallest North American bird, is an endangered crane species named for its whooping sound. Along with the Sandhill Crane, it is one of only two crane species found in North America. The whooping crane's lifespan is estimated to be 22 to 24 years in the wild...

, the male and the female take turns incubating the egg. In others, such as the cassowaries
Cassowary
The cassowaries are ratites, very large flightless birds in the genus Casuarius native to the tropical forests of New Guinea, nearby islands and northeastern Australia. There are three extant species recognized today...

, only the male incubates. The male Mountain Plover
Mountain Plover
The Mountain Plover is a medium-sized ground bird in the plover family . It is misnamed, as it lives on level land...

 incubates the female's first clutch, but if she lays a second, she incubates it herself. In Hoatzin
Hoatzin
The Hoatzin , also known as the Hoactzin, Stinkbird, or Canje Pheasant, is a species of tropical bird found in swamps, riverine forest and mangrove of the Amazon and the Orinoco delta in South America...

s, 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 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 the Black-billed
Black-billed Cuckoo
The Black-billed Cuckoo, Coccyzus erythropthalmus, is a cuckoo.Adults have a long brown tail and a black bill. The head and upper parts are brown and the underparts are white. There is a red ring around the eye. Juveniles are drabber, and the eye ring is greenish.Their breeding habitat is edges of...

 and Yellow-billed Cuckoo
Yellow-billed Cuckoo
The Yellow-billed Cuckoo, Coccyzus americanus, is a cuckoo. Common folk-names for this bird in the southern United States are Rain Crow and Storm Crow...

s) to 85 days (the Wandering Albatross
Wandering Albatross
The Wandering Albatross, Snowy Albatross or White-winged Albatross, Diomedea exulans, is a large seabird from the family Diomedeidae, which has a circumpolar range in the Southern Ocean. It was the first species of albatross to be described, and was long considered the same species as the Tristan...

 and the Brown Kiwi). In these latter, the incubation is interrupted; the longest uninterrupted period is 64 to 67 days in the Emperor Penguin
Emperor Penguin
The Emperor Penguin is the tallest and heaviest of all living penguin species and is endemic to Antarctica. The male and female are similar in plumage and size, reaching in height and weighing anywhere from . The dorsal side and head are black and sharply delineated from the white belly,...

. 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. 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.

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. 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.

Incubation periods for birds

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...

Incubation Period (days)
Chicken
Chicken
The chicken is a domesticated fowl, a subspecies of the Red Junglefowl. As one of the most common and widespread domestic animals, and with a population of more than 24 billion in 2003, there are more chickens in the world than any other species of bird...

 
20–22
Duck
Duck
Duck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...

 
26–28
Eagle
Eagle
Eagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...

 
35-36
Finch
Finch
The true finches are passerine birds in the family Fringillidae. They are predominantly seed-eating songbirds. Most are native to the Northern Hemisphere, but one subfamily is endemic to the Neotropics, one to the Hawaiian Islands, and one subfamily – monotypic at genus level – is found...

 
11–14
Goose
Goose
The word goose is the English name for a group of waterfowl, belonging to the family Anatidae. This family also includes swans, most of which are larger than true geese, and ducks, which are smaller....

 
25–28
Ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...

 
35-45
Parrot
Parrot
Parrots, also known as psittacines , are birds of the roughly 372 species in 86 genera that make up the order Psittaciformes, found in most tropical and subtropical regions. The order is subdivided into three families: the Psittacidae , the Cacatuidae and the Strigopidae...

 
17–31
Pheasant
Pheasant
Pheasants refer to some members of the Phasianinae subfamily of Phasianidae in the order Galliformes.Pheasants are characterised by strong sexual dimorphism, males being highly ornate with bright colours and adornments such as wattles and long tails. Males are usually larger than females and have...

 
24
Pigeon  10–18
Quail
Quail
Quail is a collective name for several genera of mid-sized birds generally considered in the order Galliformes. Old World quail are found in the family Phasianidae, while New World quail are found in the family Odontophoridae...

 
21–23
Swan
Swan
Swans, genus Cygnus, are birds of the family Anatidae, which also includes geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Sometimes, they are considered a distinct subfamily, Cygninae...

 
33–36
Turkey
Turkey (bird)
A turkey is a large bird in the genus Meleagris. One species, Meleagris gallopavo, commonly known as the Wild Turkey, is native to the forests of North America. The domestic turkey is a descendant of this species...

 
28

Mammalian incubation


Very few mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s lay eggs. In perhaps the best known example, the platypus
Platypus
The platypus is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young...

, the eggs develop in utero
In utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...

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). After laying her eggs, the female curls around them. The incubation period is divided into three phases. In the first phase, the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...

 has no functional organs and relies on the yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...

 for sustenance. The yolk is absorbed by the developing young. During the second phase, the digits develop and, in the last phase, the egg tooth
Egg tooth
In some egg-laying animals, the egg tooth is a small, sharp, cranial protuberance used by offspring to break or tear through the egg's surface during hatching...

 appears. The only other egg-laying mammal is the echidna
Echidna
Echidnas , also known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. There are four extant species, which, together with the platypus, are the only surviving members of that order and are the only extant mammals that lay eggs...

.

Reptilian incubation


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.

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