A Rooster (male chicken)
A Rooster (male chicken)
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Galliformes
Family: Phasianidae
Genus: Gallus
Species: G. gallus

The chicken (Gallus gallus) is one of humankind's most common and wide-spread domestic animals. The chicken is believed to be descended from the wild Indian and south-east Asian red junglefowl (also Gallus gallus). They are members of the Phasianidae, or pheasant, family of birds.


Chickens benefit humans greatly as a source of food, both from their meat and their eggs. People in many cultures have admired the good qualities of chickens and have worked to create useful and beautiful breeds. The chicken also has played roles in Chinese religion, Hindu ceremonies, ancient Greece mythology, ancient Roman oracles, Central European folk tales, and in traditional Jewish practice, and are referred to Biblical passages. On the other hand, chickens have often been the victims of human cruelty, for instance in the sport of cockfighting and in inhumane practices on modern factory farms.

Chicken ancestry: The red junglefowl

Red junglefowl

The range of the red junglefowl stretches from northeast India eastwards across southern China and down into Malaysia and Indonesia. They are about the size of the smaller breeds of domestic chicken, weighing about 0.5 to 1 kilograms (1 to 2 pounds) (Hopf 1982).

Male and female birds show very strong sexual dimorphism. Male junglefowl are larger and they have large red fleshy wattles on the head. The long, bright gold, and bronze feathers form a "shawl" or "cape" over the back of the bird from the neck to the lower back. The tail is composed of long, arching feathers that initially look black but shimmer with blue, purple, and green in good light. The female's plumage is typical of this family of birds in being cryptic and designed for camouflage as she looks after the eggs and chicks. She also has no fleshy wattles or comb on her head.

Junglefowl live in small groups. As in other members of the pheasant family, newly-hatched junglefowl chicks are fully feathered and are able to walk and find food for themselves. The mother hen watches over the chicks and leads them to feeding areas. The roosters seem to play a role in watching over the flock and warning the others of danger (Masson 2003).

During the breeding season, the male birds announce their presence with the well known "cock-a-doodle-doo" call. This serves both to attract potential mates and to make other male birds in the area aware of the risk of fighting a breeding competitor. The lower leg just behind and above the foot has a long spur for just this purpose. Their call structure is complex and they have distinctive alarm calls for aerial and ground predators to which others react appropriately (Collias 1987).

Flight in these birds is almost purely confined to reaching their roosting areas at sunset in trees or any other high and relatively safe places free from ground predators, and for escape from immediate danger through the day. They feed on the ground, eating mainly seeds and insects.


A day-old chick

The red junglefowl was probably first domesticated in India around 3000 B.C.E. It is thought that they were first kept as pets rather than as a source of food, although both the birds and their eggs were eaten. Fights were staged between roosters and cockfighting became a popular form of entertainment; it remained so until modern times when these type of bloodsports were banned in many countries.

Domestic chickens spread from India east to China about 1400 B.C.E. and west to Egypt about the same time. They entered Europe by way of Persia and Greece soon after. They seem to have been introduced to South America either by Polynesian or Chinese visitors and were later introduced to the rest of the world by European colonists (Hopf 1982).

Domesticated chickens differ from wild junglefowl in several features. They are usually larger. They are much less nervous and afraid of humans.

Distinct breeds of chickens arose in different locations. In most places, the ability of the rooster to fight was the most important feature chicken breeders selected for, while in both China and ancient Rome chicken meat became important as food and larger breeds were developed. The Chinese developed fancy breeds with beautiful and unusual plumage, while the Romans breed white chickens in order to sacrifice them to their gods (Hopf 1982).


Male chickens are known as roosters in the United States, Canada, and Australia; in the United Kingdom they are known as cocks when over one year of age, or cockerels when under one year of age. Castrated roosters are called capons. Female chickens over a year old are known as hens. Young females under a year old are known as pullets. Roosters can usually be differentiated from hens by their striking plumage, marked by long flowing tails and bright pointed feathers on their necks. Baby chickens are call chicks.


Rooster crowing during daylight hours

Domestic chickens are not capable of long distance flight, although they are generally capable of flying for short distances such as over fences. Chickens will sometimes fly to explore their surroundings, but usually do so only to flee perceived danger. Because of the risk of escape, chickens raised in open-air pens generally have one of their wings clipped by the breeder—the tips of the longest feathers on one of the wings are cut, resulting in unbalanced flight, which the bird cannot sustain for more than a few meters.

Chickens often scratch at the soil to search for insects and seeds.

Chickens are gregarious birds and live together as a flock. They have a communal approach to the incubation of eggs and raising of young. Individual chickens in a flock will dominate others, establishing a "pecking order," with dominant individuals having priority for access to food and nesting locations. In the wild, this helps to keep order in the flock, while in domestication it can often lead to injuries or death (Short 1993).

Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Incidents of cannibalism can occur when a curious bird pecks at a preexisting wound or during fighting (even among female birds). This is exacerbated in close quarters. In commercial egg and meat production, this is controlled by trimming the beak (removal of two thirds of the top half and occasionally one third of the lower half of the beak).

Chickens will try to lay in nests that already contain eggs, and have been known to move eggs from neighboring nests into their own. The result of this behavior is that a flock will use only a few preferred locations, rather than having a different nest for every bird. Some farmers use fake eggs made from plastic or stone to encourage hens to lay in a particular location.

Hens can be extremely stubborn about always laying in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other.

Contrary to popular belief, roosters do not crow only at dawn, but may crow at any time of the day or night. Their crowing—a loud and sometimes shrill call—is a territorial signal to other roosters. However, crowing may also result from sudden disturbances within their surroundings.

When a rooster finds food, he may call the other chickens to eat it first. He does this by clucking in a high pitch as well as picking up and dropping the food. This behavior can also be observed in mother hens, calling their chicks.

In some cases, the rooster will drag the wing opposite the hen on the ground, while circling her. This is part of chicken courting ritual. When a hen is used to coming to his "call" the rooster may mount the hen and proceed with the fertilization.

Chicken eggs vary in color depending on the hen, typically ranging from bright white to shades of brown and even blue, green, and recently reported purple (found in South Asia) (Araucana varieties).

Sometimes a hen will stop laying and instead will focus on the incubation of eggs, a state that is commonly known as going broody. A broody chicken will sit fast on the nest, and protest or peck in defense if disturbed or removed, and will rarely leave the nest to eat, drink, or dust bathe. While brooding, the hen maintains constant temperature and humidity, as well as turning the eggs regularly.

At the end of the incubation period, which is an average of 21 days, the eggs (if fertilized) will hatch, and the broody hen will take care of her young. Since individual eggs do not all hatch at exactly the same time (the chicken can only lay one egg approximately every 25 hours), the hen will usually stay on the nest for about two days after the first egg hatches. During this time, the newly-hatched chicks live off the egg yolk they absorb just before hatching. The hen can sense the chicks peeping inside the eggs, and will gently cluck to stimulate them to break out of their shells. If the eggs are not fertilized by a rooster and do not hatch, the hen will eventually lose interest and leave the nest.

Modern egg-laying breeds rarely go broody, and those that do often stop part-way through the incubation cycle. Some breeds, such as the Cochin, Cornish, and Silkie, regularly go broody and make excellent maternal figures. Chickens used in this capacity are known as utility chickens.

Chicken farming

Free range chickens


Throughout history, chickens, although very common, have almost always been of secondary importance in farming communities. Small flocks were kept on farms, and chicken meat and eggs were often an important source of family food or extra income.

After the fall of the Roman Empire, little attention was paid in the West to chicken breeding until the 1800s when more productive breeds began to be developed. The Leghorn has become the most popular breed for egg production, while Rhode Island Reds, Plymouth Rocks, and some others are the most popular for meat (Hopf 1982).

On farms in the United States, eggs used to be practically the same as currency, with general stores buying eggs for a stated price per dozen. Egg production peaks in the early spring, when farm expenses are high and income is low. On many farms, the flock was the most important source of income, though this was often not appreciated by the farmers, since the money arrived in many small payments. Eggs were a farm operation where even small children could make a valuable contribution.

The major milestone in twentieth century poultry production was the discovery of vitamin D, which made it possible to keep chickens in confinement year-round. Before this, chickens did not thrive during the winter (due to lack of sunlight), and egg production, incubation, and meat production in the off-season were all very difficult, making poultry a seasonal and expensive proposition. Year-round production lowered costs, especially for broilers.

At the same time, egg production was increased by scientific breeding. Improvements in production and quality were accompanied by lower labor requirements. In the 1930s through the early 1950s, having 1,500 hens was considered to be a full-time job for a farm family. In the late 1950s, egg prices had fallen so dramatically that farmers typically tripled the number of hens they kept, putting three hens into what had been a single-bird cage or converting their floor-confinement houses from a single deck of roosts to triple-decker roosts. Not long after this, prices fell still further and large numbers of egg farmers left the business.

This fall in profitability, accompanied by a general fall in prices to the consumer, resulted in poultry and eggs losing their status as luxury foods. This marked the beginning of the transition from family farms to larger, vertically integrated operations. The vertical integration of the egg and poultry industries was a late development, occurring after all the major technological changes had been in place for years (including the development of modern broiler rearing techniques, the adoption of the Cornish Cross broiler, the use of laying cages, etc.).

By the late 1950s, poultry production had changed dramatically. Large farms and packing plants could grow birds by the tens of thousands. Chickens could be sent to slaughterhouses for butchering and processing into prepackaged commercial products to be frozen or shipped fresh to markets or wholesalers. Meat-type chickens currently grow to market weight in six to seven weeks whereas only 50 years ago it took three times as long. This is due to genetic selection and nutritional modifications (and not the use of growth hormones, which are illegal for use in poultry in the United States and many other countries). Once a meat consumed only occasionally, the common availability and lower cost has made chicken a common meat product within developed nations. Growing concerns over the cholesterol content of red meat in the 1980s and 1990s further resulted in increased consumption of chicken.

Modern chicken farming

Modern egg production

Today, eggs are produced on large egg ranches on which environmental parameters are controlled. Chickens are exposed to artificial light cycles to stimulate egg production year-round. In addition, it is a common practice to induce molting through manipulation of light and the amount of food they receive in order to further increase egg size and production.

On average, a chicken lays one egg a day for a number of days (a "clutch"), then does not lay for one or more days, then lays another clutch. Originally, the hen presumably laid one clutch, became broody, and incubated the eggs. Selective breeding over the centuries has produced hens that lay more eggs than they can hatch. Some of this progress was ancient, but most occurred after 1900. In 1900, average egg production was 83 eggs per hen per year. In 2000, it was well over 300.

In the United States, laying hens are butchered after their second egg laying season. In Europe, they are generally butchered after a single season. The laying period begins when the hen is about 18-20 weeks old (depending on breed and season). Males of the egg-type breeds have little commercial value at any age, and all those not used for breeding (roughly fifty percent of all egg-type chickens) are killed soon after hatching. The old hens also have little commercial value. Thus, the main sources of poultry meat 100 years ago (spring chickens and stewing hens) have both been entirely supplanted by meat-type broiler chickens.

Traditionally, chicken production was distributed across the entire agricultural sector. In the twentieth century, it gradually moved closer to major cities to take advantage of lower shipping costs. This had the undesirable side effect of turning the chicken manure from a valuable fertilizer that could be used profitably on local farms to an unwanted byproduct. This trend may be reversing itself due to higher disposal costs on the one hand and higher fertilizer prices on the other, making farm regions attractive once more.

Small scale and hobby chicken raising

Orpington shown at a fair

In most of the world, small flocks of chickens are still kept on farms and homesteads as they have been throughout history. In addition some people raise chickens as a hobby or as pets.

Purebred chickens are shown at shows and agricultural fairs. The American Poultry Association recognizes 113 different chicken breeds. Part of their interest is to preserve breeds that are in danger of going extinct because they are no longer being used in factory farming (Damerow 1995).

Concerns with modern chicken farming

Humane treatment

Animal welfare groups have frequently targeted the poultry industry for engaging in practices that they believe to be inhumane. Many animal welfare advocates object to killing chickens for food, the "factory farm conditions" under which they are raised, methods of transport, and slaughter. PETA and other groups have repeatedly conducted undercover investigations at chicken farms and slaughterhouses, which they allege confirm their claims of cruelty.

Laying hens are routinely debeaked to prevent fighting. Because beaks are sensitive, trimming them without anesthesia is considered inhumane by some. It is also argued that the procedure causes life-long discomfort. Conditions in intensive chicken farms may be unsanitary, allowing the proliferation of diseases such as salmonella and E. coli. Chickens may be raised in total darkness. Rough handling and crowded transport during various weather conditions and the failure of existing stunning systems to render the birds unconscious before slaughter have also been cited as welfare concerns.

Another animal welfare concern is the use of selective breeding to create heavy, large-breasted birds, which can lead to crippling leg disorders and heart failure for some of the birds. Concerns have been raised that companies growing single varieties of birds for eggs or meat are increasing their susceptibility to disease.

Human concerns


Antibiotics have been used on poultry in large quantities since the Forties. This is because it was found that the byproducts of antibiotic production—which were being fed to chickens because of high level of vitamin B12 in the antibiotic-producing mold after removal of the antibiotics—produced higher growth than could be accounted for by just the B12. Eventually it was discovered that the trace amounts of antibiotics remaining in the byproducts accounted for this growth. The mechanism is apparently the adjustment of intestinal flora, favoring "good" bacteria while suppressing "bad" bacteria, and thus the goal of antibiotics as a growth promoter is the same as for probiotics. Because the antibiotics used are not absorbed by the gut, they do not put antibiotics into the meat or eggs (Ewing 1963).

Antibiotics are used routinely in poultry for this reason, and also to prevent and treat disease. Many contend that this puts humans at risk as bacterial strains develop stronger and stronger resistances (National Research Council 1999). Critics of this view point out that, after six decades of heavy agricultural use of antibiotics, opponents of antibiotics must still make arguments about theoretical risks, since actual examples are hard to come by. Those antibiotic-resistant strains of human diseases whose origin is known apparently originated in hospitals rather than farms.


A free roaming bantam chickens on the streets of downtown Key West, Florida

According to Consumer Reports, "1.1 million or more Americans [are] sickened each year by undercooked, tainted chicken" (Consumer Reports 2005). A USDA study discovered E.Coli in 99 percent of supermarket chicken, the result of chicken butchering not being a sterile process. Feces tend to leak from the carcass until the evisceration stage, and the evisceration stage itself gives an opportunity for the interior of the carcass to receive intestinal bacteria. (So does the skin of the carcass, but the skin presents a better barrier to bacteria and reaches higher temperatures during cooking).

Before 1950, this bacterial risk was contained largely by not eviscerating the carcass at the time of butchering, deferring this until the time of retail sale or in the home. This gave the intestinal bacteria less opportunity to colonize the edible meat. The development of the "ready-to-cook broiler" in the 1950s added convenience while introducing risk, under the assumption that end-to-end refrigeration and thorough cooking would provide adequate protection.

E. Coli can be killed by proper cooking times, but there is still some risk associated with it, and its near-ubiquity in commercially-farmed chicken is troubling to some. Irradiation has been proposed as a means of sterilizing chicken meat after butchering; while proper storage, handling, and cooking are always important (CDC 2019).

Avian influenza

There is also a risk that the crowded conditions in many chicken farms will allow avian influenza to spread quickly. A United Nations press release states: "Governments, local authorities and international agencies need to take a greatly increased role in combating the role of factory-farming, commerce in live poultry, and wildlife markets which provide ideal conditions for the virus to spread and mutate into a more dangerous form..." (Greger 2006).


Farming of chickens on an industrial scale relies largely on high protein feeds derived from soybeans; in the European Union the soybean dominates the protein supply for animal feed, and the poultry industry is the largest consumer of such feed. Giving the feed to chickens means the protein reaches humans with a much lower efficiency than through direct consumption of soybean products. Some nutrients, however, are present in chicken but not in the soybean (Brown 2017).

Chickens in religion and culture

Rhode Island Reds

The chicken is one of the Zodiac symbols of the Chinese calendar. Also in Chinese religion, a cooked chicken as a religious offering is usually limited to ancestor veneration and worship of village deities. Vegetarian deities, such as the Buddha, are not one of the recipients of such offerings. Under some observations, an offering of chicken is presented with "serious" prayer (while roasted pork is offered during a joyous celebration). In Confucian Chinese weddings, a chicken can be used as a substitute for one who is seriously ill or not available (e.g sudden death) to attend the ceremony. A red silk scarf is placed on the chicken's head and a close relative of the absent bride/groom holds the chicken so the ceremony may proceed. However, this practice is rare today.

In Indonesia, the chicken has great significance during the Hindu cremation ceremony. A chicken is considered a channel for evil spirits, which may be present during the ceremony. A chicken is tethered by the leg and kept present at the ceremony for its duration to ensure that any evil spirits present during the ceremony go into the chicken and not the family members present. The chicken is then taken home and returns to its normal life.

In ancient Greece, the chicken was not normally used for sacrifices, perhaps because it was still considered an exotic animal. Because of its valor, the cock is found as an attribute of Ares, Heracles, and Athena. The Greeks believed that even lions were afraid of cocks. Several of Aesop's fables reference this belief. In the cult of Mithras, the rooster was a symbol of the divine light and a guardian against evil.

The first pictures of chickens in Europe are found on Corinthian pottery of the seventh century B.C.E. The poet Cratinus (mid fifth century B.C.E., according to the later Greek author Athenaeus) calls the chicken "the Persian alarm." In Aristophanes's comedy The Birds (414 B.C.E.), a chicken is called "the Median bird," which points to an introduction from the East. Pictures of chickens are found on Greek red figure and black-figure pottery.

The ancient Romans used chickens for oracles, both when flying ("ex avibus") and when feeding ("auspicium ex tripudiis"). The hen ("gallina") gave a favorable omen ("auspicium ratum") when appearing from the left (Cic.,de Div. ii.26), like the crow and the owl.

For the oracle "ex tripudiis," according to Cicero (Cic. de Div. ii.34), any bird could be used, but normally only chickens ("pulli") were consulted. The chickens were cared for by the pullarius, who opened their cage and fed them pulses or a special kind of soft cake when an augury was needed. If the chickens stayed in their cage, made noises ("occinerent"), beat their wings or flew away, the omen was bad; if they ate greedily, the omen was good.

In 249 B.C.E., the Roman general Publius Claudius Pulcher had his chickens thrown overboard when they refused to feed before the battle of Drepana, saying "If they won't eat, perhaps they will drink." He promptly lost the battle against the Carthaginians and 93 Roman ships were sunk. Back in Rome, he was tried for impiety and heavily fined.

In the Bible, Jesus prophesied the betrayal by Peter: "Jesus answered, 'I tell you, Peter, before the rooster crows today, you will deny three times that you know me.'" (Luke 22:34) Thus it happened (Luke 22:61), and Peter cried bitterly. This made the cock a symbol for both vigilance and betrayal.

Earlier, Jesus compares himself to a mother hen when talking about Jerusalem: "O Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you, how often I have longed to gather your children together, as a hen gathers her chicks under her wings, but you were not willing." (Matthew 23:37; also Luke 13:34).

In many Central European folk tales, Satan is believed to flee at the first crowing of a rooster.

In traditional Jewish practice, a chicken is swung around the head and then slaughtered on the afternoon before Yom Kippur, the Day of Atonement, in a ritual called kapparos. The sacrifice of the chicken is to receive atonement, for the bird takes on all the person's sins in kapparos. The meat is then donated to the poor. A woman brings a hen for the ceremony, while a man brings a rooster. Although not actually a sacrifice in the biblical sense, the death of the chicken reminds the penitent sinner that his or her life is in God's hands.

The Talmud speaks of learning "courtesy toward one's mate" from the rooster. This might refer to the fact that when a rooster finds something good to eat, he sometimes calls his hens to eat first.



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