Chicken (Gallus gallus domesticus)
Domestic animalsBirdsGalliformes
Domestic hens. Chickens descend primarily from the red junglefowl of South and Southeast Asia.
Image: Leoadec, CC BY-SA 3.0, via Wikimedia Commons.
Overview
The chicken is a domesticated ground bird of the order Galliformes, usually written as Gallus gallus domesticus and generally treated as a domesticated form of the red junglefowl, Gallus gallus, a bird of forest edges, scrub and bamboo thickets in South and Southeast Asia. Compact-bodied, short-winged and heavy-footed, it walks and scratches far more than it flies. The fleshy comb above the head and the paired wattles below the bill are its most recognisable features, and both vary a great deal with sex, breed and individual condition.
By any reasonable count the chicken is the most numerous bird on Earth, and by a wide margin rather than a narrow one. That is a direct consequence of how widely people keep it: unlike almost every other bird, its numbers track human settlement rather than any natural habitat. Breeds differ enormously in size, plumage, comb shape and temperament, so a description of "the chicken" is always a description of a very variable domestic animal rather than of one uniform wild species.
Much of what makes the chicken interesting is behavioural and retained from its wild ancestry: scratch-and-peck foraging, dust bathing, roosting off the ground at dusk, a varied vocal repertoire, precocial chicks that walk and feed themselves within about a day, and consistent social relationships within a flock. Specific figures for size, maturity and longevity differ so much between breeds and settings that they are best treated as ranges and checked against authoritative ornithological and animal-science sources.
Habitat & Range
The chicken has no natural habitat of its own in the way a wild bird does. It lives where people live, from smallholdings and village edges to gardens, mixed farmland and managed settings across most of the inhabited world, in climates ranging from cold temperate to hot and humid. Hardiness varies by breed, and the traits that suit a bird to one climate — feather density, body size, comb size — are among the features that differ most between regional breeds.
Its wild ancestor gives a clearer picture of the habitat the species is built for. Red junglefowl are typically associated with forest edge, secondary growth, bamboo, scrub and the mosaic of clearings and thickets that sits between dense forest and open ground. That is a shaded, structurally cluttered environment with loose leaf litter to scratch through, dry patches for dust bathing, and branches to roost on above the ground. Domestic chickens still behave as though they expect those elements, which is why cover, litter and elevated roosting places recur in descriptions of their behaviour.
Free-living feral populations have also established on some islands and in some warm regions where escaped or released birds persist without direct human management. These populations are usually local and variable, and how self-sustaining any given one is depends on climate, predators and continued contact with kept birds.
Diet
Chickens are omnivorous ground foragers. Left to search for themselves, they take a mixed diet of seeds and grains, green shoots and leaves, fallen fruit, insects, worms, snails and other small invertebrates, and they will investigate almost any small item that moves. The characteristic method is scratching: the bird rakes backwards with its feet to expose the surface beneath litter or soil, steps back, and inspects what has been uncovered. Like other birds they have no teeth, so food is swallowed whole and ground in the muscular gizzard, commonly assisted by small stones and grit picked up while foraging. What an individual bird actually eats depends heavily on the setting, the season and what is available. This page describes foraging ecology only; it does not offer feeding plans, quantities or dietary recommendations for birds in anyone's care.
Behavior
Comb and wattles are worth describing first because they do more than decorate. Both are unfeathered, fleshy and richly supplied with blood vessels. Birds do not sweat, and these bare, well-vascularised surfaces are understood to help shed excess heat, which is one reason comb size tends to differ between breeds developed in hot and in cold regions. They also serve in signalling: comb and wattle size, colour and condition differ with sex, age, breed and individual state, and they are typically more developed in males. Several distinct comb shapes — single, rose, pea and others — are recognised in breed descriptions.
Dust bathing is a routine maintenance behaviour rather than a curiosity. A bird works itself into loose dry soil, sand or litter, scratches and wing-flicks the material down through its plumage, then stands and shakes it out in a cloud. The behaviour is generally associated with managing excess feather lipids and with reducing external parasites, and it is often social, with several birds using the same hollow in succession or crowding into it together.
Flocks show documented social structure. Individuals form consistent dominance relationships that are expressed through displacement, threat postures and pecks, and priority of access to resources tends to follow those relationships. The everyday phrase "pecking order" is usually traced back to early observations of hens, but it is better understood as documented flock structure than as a law of nature: the pattern depends on group size, stability, familiarity between birds, sex composition and available space, it can be reshuffled when birds join or leave, and it is not always a tidy straight line from top to bottom.
Other behaviours are equally characteristic. Chickens roost off the ground at dusk where they can, a habit inherited from an ancestor that slept in branches. They are capable of strong flapping flight over short distances — enough to reach a branch, fence or low roof — but not of sustained flight, and heavy breeds fly far less than light ones. Their vocal repertoire is varied, and researchers have described context-specific calls, including alarm calls that differ according to the kind of threat, along with food-related calls and the contact calls that pass between a hen and her chicks. Broodiness — the tendency of a hen to sit and incubate — varies markedly between breeds and individuals.
Human Interaction & Conservation
No bird is more closely bound up with human life. Chickens have travelled with people along trade routes and voyaging routes for thousands of years, and they appear across a very wide range of cultures in ritual, symbolism, timekeeping and folklore, from the crowing cock as a marker of dawn to the many regional breeds developed for appearance and show. In some regions birds were historically kept for fighting, a practice now restricted or prohibited in many jurisdictions; the legal position differs by country and is not something this page states as fact for any particular place.
The chicken has also had an outsized role in science. The developing chicken embryo has long been one of the standard subjects in developmental biology, and studies of fowl behaviour contributed early evidence about dominance relationships in animal groups. Poultry genetics is likewise one of the better-documented areas of domestic-animal research, which is why questions about the species' ancestry can be discussed in more detail than for most domesticated animals.
This profile is educational natural history. Questions about the health, handling or welfare of individual birds should go to a qualified veterinarian and to species-specific welfare organisations, not to a general encyclopedia page.
Distribution
The chicken's original range is the range of its wild ancestors: red junglefowl occur across parts of South and Southeast Asia, and grey junglefowl in peninsular India. From that starting point domestic birds spread with people, moving through Asia and into western Eurasia, across Africa, and out into the Pacific with island-voyaging communities, before reaching the Americas in quantity following European contact. The general outline is well established; the precise routes and timings are an active research area and specific dates should be checked against current scholarship rather than assumed.
Today chickens are present essentially wherever people live permanently, on every continent except Antarctica. Free-living feral flocks persist in some warm regions and on some islands. Distribution has therefore changed in a way no wild bird's has: it is governed by human settlement and movement, not by climate envelopes or migration routes, and it continues to shift as breeds are moved between regions.
Senses & Adaptations
Vision dominates. The eyes are placed towards the sides of the head, giving a wide field of view useful for detecting movement while the bird's attention is on the ground, at the cost of the narrow binocular overlap a forward-eyed predator enjoys. Like other birds, chickens have more cone types than humans do, together with coloured oil droplets in the retina, and are generally described as having rich colour vision extending into shorter wavelengths than people can see. Ground-feeding birds also rely on quick head movements to stabilise the visual scene between steps.
Beyond vision, the bill and feet do much of the investigative work, and the bill tip is sensitive enough to sort small items from soil and litter. Hearing supports a varied vocal repertoire. Structurally the bird is built for walking and scratching rather than flying: strong legs and feet, a heavy body relative to wing area, and flight muscle suited to short, powerful bursts to reach a roost or escape a threat rather than to sustained travel. The bare comb and wattles add a thermoregulatory surface in an otherwise well-insulated, feather-covered animal.
Lifespan & Life Stages
Chicks are precocial. Incubation typically runs about three weeks, and hatchlings emerge covered in down with their eyes open. Within roughly a day they walk, follow the hen and peck at small items for themselves; the hen leads them to food, calls them, and broods them for warmth rather than carrying meals to a nest. Down is gradually replaced by juvenile and then adult plumage over the following weeks and months. Young birds are usually called pullets and cockerels before they are described as hens and roosters, and sexual maturity is commonly reached somewhere in the region of five to eight months, varying with breed, sex, season and conditions.
Free-living and feral birds: longevity is largely set by predation, disease and weather rather than by any internal limit, and feral birds are rarely followed as individuals, so figures are poorly documented and best described qualitatively. Many do not reach the ages that protected birds can.
Birds under human care: individuals kept in protected settings are commonly reported to live several years, and some reach roughly a decade or more. These figures differ widely by breed, sex, environment and record-keeping quality, and reported maxima for exceptional individuals should not be read as typical. The two situations are not comparable and should not be averaged together.
Conservation Context
The domestic chicken is not a wild species and is not assessed for extinction risk in the way wild birds are; abundance is a function of how many people keep it. Conservation attention within the domestic form is instead directed at breed diversity, since many regional and traditional breeds are held in small populations, and national and international livestock genetic-resource programmes track that diversity.
The wild ancestors are a separate matter. Red junglefowl and grey junglefowl are wild birds assessed on the IUCN Red List, and one documented concern for wild junglefowl is genetic introgression from domestic birds where the two overlap, in addition to habitat change and hunting pressure. No conservation status is permanent: categories are reassessed as evidence changes, so the current listing for any junglefowl species should be read directly from the IUCN Red List rather than taken from a secondary page.
What the Name Covers
"Chicken" refers to the domestic bird as a whole, at any age and either sex. English keeps separate words for the life stages and sexes: an adult female is a hen, an adult male a rooster or cock, young birds are pullets and cockerels, and newly hatched birds are chicks. Usage varies by region — cock is the older and still standard term in British English, rooster is usual in North American English — and a great many breed and landrace names sit beneath the single word "chicken".
The scientific naming is not fully settled either. The domestic bird is most often written Gallus gallus domesticus, treating it as a domesticated form of the red junglefowl, Gallus gallus; some authorities instead use Gallus domesticus as a species name. Both conventions appear in reputable sources, and the choice reflects a broader disagreement about how domesticated animals should be named relative to their wild ancestors.
Two further clarifications are worth making. "Fowl" is a broader and older word that in different contexts covers chickens specifically, gallinaceous birds generally, or birds kept by people; and "junglefowl" refers to the wild Gallus species of Asia, not to feral chickens, even though the two are sometimes confused where their ranges meet.
Domestic, Feral and Wild
The chicken is a fully domesticated animal, descended chiefly from the red junglefowl (Gallus gallus) of South and Southeast Asia. Genetic evidence has also indicated a contribution from the grey junglefowl (Gallus sonneratii) of peninsular India, an introgression commonly associated with the yellow skin found in many breeds. That grey-junglefowl contribution is best stated cautiously: it is a well-discussed finding rather than a settled account of the whole genome, and the relative contributions of the Gallus species remain under study. Domestication took place several thousand years ago, and both its timing and whether it happened once or several times are debated, so a single confident date should be treated with suspicion.
Feral chickens are domestic birds living without direct human management, and they are not the same thing as wild junglefowl. Feral flocks tend to retain domestic plumage variation and breed traits, whereas wild junglefowl are a distinct wild species with their own ecology and conservation assessment. Where feral chickens and wild junglefowl overlap in Asia the distinction can genuinely blur through interbreeding, which is precisely why the introgression question matters to people studying wild populations.
Compare With Related Animals
Side-by-side comparisons covering identification, taxonomy, habitat and behaviour.
- Chicken vs Duck
- Chicken vs Goose
- Chicken vs Pigeon
- Chicken vs Wild Turkey
- Peacock vs Chicken
- All animal comparisons
More photos of the chicken
A domestic hen foraging in grass. Chickens are ground-foraging omnivores that scratch for seeds and invertebrates.
Image: Jörg Hempel, CC BY-SA 3.0 de, via Wikimedia Commons.
Frequently Asked Questions — Chicken
What is the domestic chicken descended from?
What are a chicken’s comb and wattles for?
Why do chickens dust bathe?
Is the “pecking order” in a flock real?
Can newly hatched chicks walk and feed themselves?
Sources and further reading
Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.
- UniversityAnimal Diversity Web — Gallus gallus (red junglefowl, ancestor of the chicken) — University of Michigan species account
- ReferenceEncyclopaedia Britannica — Animals reference — Editor-reviewed encyclopedia overview entries
- Wildlife referenceIUCN Red List of Threatened Species — Authoritative source for current conservation status