Egg incubation

A female Mallard duck incubates her eggs

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]

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
Other Languages
Адыгэбзэ: Къишын
Afrikaans: Inkubasie
العربية: حضن البيض
català: Incubació
Deutsch: Brut
eesti: Haudumine
español: Incubación
Esperanto: Kovado
euskara: Inkubazio
हिन्दी: ऊष्मायन
עברית: דגירה
Kreyòl ayisyen: Kouve
македонски: Квачење
Bahasa Melayu: Pengeraman telur
Mìng-dĕ̤ng-ngṳ̄: Bô-luāng
Nederlands: Broeden
norsk: Ruging
português: Incubação
română: Clocire
Simple English: Avian incubation
українська: Висиджування яєць
Tiếng Việt: Ấp trứng
walon: Covisse
粵語: 菢蛋