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Chicken

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Chicken
Male and female chicken sitting together.jpg
A rooster (left) and hen (right) perching on a roost
Domesticated
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Galliformes
Family: Phasianidae
Genus: Gallus
Species:
Subspecies:
G. g. domesticus
Trinomial name
Gallus gallus domesticus
GLW 2 global distributions of c) chickens.tif
Chicken distribution

The chicken (Gallus gallus domesticus) is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl[1] that are originally from Southeastern Asia. Rooster or cock is a term for an adult male bird, and a younger male may be called a cockerel. A male that has been castrated is a capon. An adult female bird is called a hen and a sexually immature female is called a pullet. Humans now keep chickens primarily as a source of food (consuming both their meat and eggs) and as pets. Traditionally they were also bred for cockfighting, which is still practiced in some places.

Chickens are one of the most common and widespread domestic animals, with a total population of 23.7 billion as of 2018,[2] up from more than 19 billion in 2011. There are more chickens in the world than any other bird. There are numerous cultural references to chickens – in myth, folklore and religion, and in language and literature.

Genetic studies have pointed to multiple maternal origin theories of within South Asia, Southeast Asia, and East Asia,[3] but the clade found in the Americas, Europe, the Middle East and Africa originated from the Indian subcontinent. From ancient India, the chicken spread to the Eastern Mediterranean. They appear in Egypt in the mid-15th century BC, with the "bird that gives birth every day" having come from the land between Syria and Shinar, Babylonia, according to the annals of Thutmose III.[4][5][6] They are known in Greece from the 5th century BC.[7] [8]

In 2011 a study in genetic and archaeological[9] evidence conclude that the origin of the modern-day chicken is from South-East Asia. This is the area east of India and south of China.

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Domestication

Domestication

Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A broader biological definition is that it is a coevolutionary process that arises from a mutualism, in which one species constructs an environment where it actively manages both the survival and reproduction of another species in order to provide the former with resources and/or services. The domestication of plants and animals by humans was a major cultural innovation ranked in importance with the conquest of fire, the manufacturing of tools, and the development of verbal language.

Capon

Capon

A capon is a cockerel (rooster) that has been castrated or neutered, either physically or chemically, to improve the quality of its flesh for food, and, in some countries like Spain, fattened by forced feeding.

Chicken as food

Chicken as food

Chicken is the most common type of poultry in the world. Owing to the relative ease and low cost of raising chickens—in comparison to mammals such as cattle or hogs—chicken meat and chicken eggs have become prevalent in numerous cuisines.

Cockfight

Cockfight

A cockfight is a blood sport, held in a ring called a cockpit. The history of raising fowl for fighting goes back 6,000 years. The first documented use of the word gamecock, denoting use of the cock as to a "game", a sport, pastime or entertainment, was recorded in 1634, after the term "cock of the game" used by George Wilson, in the earliest known book on the sport of cockfighting in The Commendation of Cocks and Cock Fighting in 1607. But it was during Magellan's voyage of discovery of the Philippines in 1521 when modern cockfighting was first witnessed and documented for Westerners by the Italian Antonio Pigafetta, Magellan's chronicler, in the Kingdom of Taytay.

Bird

Bird

Birds are a group of warm-blooded vertebrates constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.

Cultural references to chickens

Cultural references to chickens

There are numerous cultural references to chickens, in myth, folklore and religion, in language and in literature.

East Asia

East Asia

East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and Taiwan are all unrecognised by at least one other East Asian state due to severe ongoing political tensions in the region, specifically the division of Korea and the political status of Taiwan. Hong Kong and Macau, two small coastal quasi-dependent territories located in the south of China, are officially highly autonomous but are under Chinese sovereignty. Japan, Taiwan, South Korea, Mainland China, Hong Kong, and Macau are among the world's largest and most prosperous economies. East Asia borders Siberia and the Russian Far East to the north, Southeast Asia to the south, South Asia to the southwest, and Central Asia to the west. To the east is the Pacific Ocean and to the southeast is Micronesia.

Clade

Clade

A clade, also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, the equivalent Latin term cladus is often used in taxonomical literature.

Americas

Americas

The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World.

Africa

Africa

Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 including adjacent islands, it covers 6% of Earth's total surface area and 20% of its land area. With 1.4 billion people as of 2021, it accounts for about 18% of the world's human population. Africa's population is the youngest amongst all the continents; the median age in 2012 was 19.7, when the worldwide median age was 30.4. Despite a wide range of natural resources, Africa is the least wealthy continent per capita and second-least wealthy by total wealth, behind Oceania. Scholars have attributed this to different factors including geography, climate, tribalism, colonialism, the Cold War, neocolonialism, lack of democracy, and corruption. Despite this low concentration of wealth, recent economic expansion and the large and young population make Africa an important economic market in the broader global context.

Babylonia

Babylonia

Babylonia was an ancient Akkadian-speaking state and cultural area based in central-southern Mesopotamia. A small Amorite-ruled state emerged in 1894 BC, which contained the minor administrative town of Babylon. It was a small provincial town during the Akkadian Empire but greatly expanded during the reign of Hammurabi in the first half of the 18th century BCE and became a major capital city. During the reign of Hammurabi and afterwards, Babylonia was called "the country of Akkad", a deliberate archaism in reference to the previous glory of the Akkadian Empire. It was often involved in rivalry with the older state of Assyria to the north and Elam to the east in Ancient Iran. Babylonia briefly became the major power in the region after Hammurabi created a short-lived empire, succeeding the earlier Akkadian Empire, Third Dynasty of Ur, and Old Assyrian Empire. The Babylonian Empire rapidly fell apart after the death of Hammurabi and reverted to a small kingdom.

Annals of Thutmose III

Annals of Thutmose III

The Annals of Thutmose III are composed of numerous inscriptions of ancient Egyptian military records gathered from the 18th Dynasty campaigns of Thutmose III's armies in Syro-Palestine, from regnal years 22 to 42. These recordings can be found on the inside walls of the chamber housing the "holy of holies" at the great Karnak Temple of Amun. Measuring just 25 meters in length and 12 meters wide, the space containing these inscriptions presents the largest and most detailed accounts concerning military exploits of all Egyptian kings.

Terminology

Didactic model of a chicken.
Didactic model of a chicken.

An adult male is a called a cock or (in the United States) a rooster and an adult female is called a hen.[10][11]

Other terms are:

  • Biddy: a newly hatched chicken[12][13]
  • Capon: a castrated or neutered male chicken[a]
  • Chick: a young chicken[14]
  • Chook /ʊk/: a chicken (Australia/New Zealand, informal)[15]
  • Cockerel: a young male chicken less than a year old[16]
  • Dunghill fowl: a chicken with mixed parentage from different domestic varieties.[17]
  • Pullet: a young female chicken less than a year old.[18] In the poultry industry, a pullet is a sexually immature chicken less than 22 weeks of age.[19]
  • Yardbird: a chicken (southern United States, dialectal)[20]

Chicken was originally a term only for an immature, or at least young, bird. In older sources, chicken as a species were typically referred to as common fowl or domestic fowl.[21]

Chicken may also mean a chick (see for example Hen and Chicken Islands).[22]

Etymology

According to Merriam-Webster, the term rooster (i.e. a roosting bird) originated in the mid- or late 18th century as a euphemism to avoid the sexual connotation of the original English cock,[23][24][25] and is widely used throughout North America. Roosting is the action of perching aloft to sleep at night.[26]

General biology and habitat

In most breeds the adult rooster can be distinguished from the hen by his larger comb.Comb of a hen.
In most breeds the adult rooster can be distinguished from the hen by his larger comb.
In most breeds the adult rooster can be distinguished from the hen by his larger comb.Comb of a hen.
Comb of a hen.

Chickens are omnivores.[27] In the wild, they often scratch at the soil to search for seeds, insects, and even animals as large as lizards, small snakes,[28] or sometimes young mice.[29]

The average chicken may live for 5–10 years, depending on the breed.[30] The world's oldest known chicken lived 16 years according to Guinness World Records.[31]

Anatomy of a chicken.
Anatomy of a chicken.
Diagram of a chicken skull.
Diagram of a chicken skull.
Eggs from different breeds
Eggs from different breeds

Roosters can usually be differentiated from hens by their striking plumage of long flowing tails and shiny, pointed feathers on their necks ('hackles') and backs ('saddle'), which are typically of brighter, bolder colours than those of females of the same breed. However, in some breeds, such as the Sebright chicken, the rooster has only slightly pointed neck feathers, the same colour as the hen's. The identification can be made by looking at the comb, or eventually from the development of spurs on the male's legs (in a few breeds and in certain hybrids, the male and female chicks may be differentiated by colour). Adult chickens have a fleshy crest on their heads called a comb, or cockscomb, and hanging flaps of skin either side under their beaks called wattles. Collectively, these and other fleshy protuberances on the head and throat are called caruncles. Both the adult male and female have wattles and combs, but in most breeds these are more prominent in males. A 'muff' or 'beard' is a mutation found in several chicken breeds which causes extra feathering under the chicken's face, giving the appearance of a beard.[32]

Domestic chickens are not capable of long-distance flight, although lighter chickens are generally capable of flying for short distances, such as over fences or into trees (where they would naturally roost). Chickens may occasionally fly briefly to explore their surroundings, but generally do so only to flee perceived danger.

Behavior

Social behaviour

Hen with chicks, India
Hen with chicks, India
Hen with chicks, Portugal
Hen with chicks, Portugal

Chickens are gregarious birds and live together in flocks. 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 food access and nesting locations. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Adding hens, especially younger birds, to an existing flock can lead to fighting and injury.

Vocalizations

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

A rooster's crowing is a loud and sometimes shrill call and sends a territorial signal to other roosters.[33] However, roosters may also crow in response to sudden disturbances within their surroundings.

Hens cluck loudly after laying an egg, and also to call their chicks. Chickens also give different warning calls when they sense a predator approaching from the air or on the ground.[34]

Crowing

The long crowing of a Berg crower
Normal length crowing (with audio). Long-crowing chickens have a longer crow.

Roosters almost always start crowing before four months of age. Although it is possible for a hen to crow as well, crowing (together with hackles development) is one of the clearest signs of being a rooster.

Rooster crowing contests

Rooster crowing contests, also known as crowing contests, are a traditional sport in several countries, such as Germany, the Netherlands, Belgium,[35] the United States, Indonesia and Japan. The oldest contests are held with longcrowers. Depending on the breed, either the duration of the crowing or the times the rooster crows within a certain time is measured.

Courtship

To initiate courting, some roosters may dance in a circle around or near a hen (a 'circle dance'), often lowering the wing which is closest to the hen.[36] The dance triggers a response in the hen[36] and when she responds to his 'call', the rooster may mount the hen and proceed with the mating.

More specifically, mating typically involves the following sequence:

  1. Male approaching the hen
  2. Male pre-copulatory waltzing
  3. Male waltzing
  4. Female crouching (receptive posture) or stepping aside or running away (if unwilling to copulate)
  5. Male mounting
  6. Male treading with both feet on hen's back
  7. Male tail bending (following successful copulation)[37]

Nesting and laying behaviour

Chicken eggs vary in colour depending on the breed, and sometimes, the hen, typically ranging from bright white to shades of brown and even blue, green, light pinkish and recently reported purple (found in South Asia) (Araucana varieties).
Chicken eggs vary in colour depending on the breed, and sometimes, the hen, typically ranging from bright white to shades of brown and even blue, green, light pinkish and recently reported purple (found in South Asia) (Araucana varieties).
Chicks before their first outing
Chicks before their first outing

Hens will often try to lay in nests that already contain eggs and have been known to move eggs from neighbouring nests into their own. The result of this behaviour is that a flock will use only a few preferred locations, rather than having a different nest for every bird. Hens will often express a preference to lay 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. There is evidence that individual hens prefer to be either solitary or gregarious nesters.[38]

A chick sitting in a person's hand
A chick sitting in a person's hand

Broodiness

Under natural conditions, most birds lay only until a clutch is complete, and they will then incubate all the eggs. Hens are then said to "go broody". The broody hen will stop laying and instead will focus on the incubation of the eggs (a full clutch is usually about 12 eggs). She will sit or 'set' on the nest, fluffing up or pecking in defense if disturbed or removed. The hen will rarely leave the nest to eat, drink, or dust-bathe.[39] While brooding, the hen maintains the nest at a constant temperature and humidity, as well as turning the eggs regularly during the first part of the incubation. To stimulate broodiness, owners may place several artificial eggs in the nest. To discourage it, they may place the hen in an elevated cage with an open wire floor.

Skull of a three-week-old chicken. Here the opisthotic bone appears in the occipital region, as in the adult Chelonian. bo = Basi-occipital, bt = Basi-temporal, eo = Opisthotic, f = Frontal, fm = Foramen magnum, fo = Fontanella, oc = Occipital condyle, op = Opisthotic, p = Parietal, pf = Post-frontal, sc = Sinus canal in supra-occipital, so = Supra-occpital, sq = Squamosal, 8 = Exit of vagus nerve.
Skull of a three-week-old chicken. Here the opisthotic bone appears in the occipital region, as in the adult Chelonian. bo = Basi-occipital, bt = Basi-temporal, eo = Opisthotic, f = Frontal, fm = Foramen magnum, fo = Fontanella, oc = Occipital condyle, op = Opisthotic, p = Parietal, pf = Post-frontal, sc = Sinus canal in supra-occipital, so = Supra-occpital, sq = Squamosal, 8 = Exit of vagus nerve.

Breeds artificially developed for egg production rarely go broody, and those that do often stop part-way through the incubation. However, other breeds, such as the Cochin, Cornish and Silkie, do regularly go broody, and make excellent mothers, not only for chicken eggs but also for those of other species — even those with much smaller or larger eggs and different incubation periods, such as quail, pheasants, ducks, turkeys, or geese.

Hatching and early life

Fertile chicken eggs hatch at the end of the incubation period, about 21 days.[36] Development of the chick starts only when incubation begins, so all chicks hatch within a day or two of each other, despite perhaps being laid over a period of two weeks or so. Before hatching, the hen can hear the chicks peeping inside the eggs, and will gently cluck to stimulate them to break out of their shells. The chick begins by 'pipping'; pecking a breathing hole with its egg tooth towards the blunt end of the egg, usually on the upper side. The chick then rests for some hours, absorbing the remaining egg yolk and withdrawing the blood supply from the membrane beneath the shell (used earlier for breathing through the shell). The chick then enlarges the hole, gradually turning round as it goes, and eventually severing the blunt end of the shell completely to make a lid. The chick crawls out of the remaining shell, and the wet down dries out in the warmth of the nest.

Hens usually remain on the nest for about two days after the first chick hatches, and during this time the newly hatched chicks feed by absorbing the internal yolk sac. Some breeds sometimes start eating cracked eggs, which can become habitual.[40] Hens fiercely guard their chicks, and brood them when necessary to keep them warm, at first often returning to the nest at night. She leads them to food and water and will call them toward edible items, but seldom feeds them directly. She continues to care for them until they are several weeks old.

Defensive behaviour

Chickens may occasionally gang up on a weak or inexperienced predator. At least one credible report exists of a young fox killed by hens.[41][42][43] A group of hens have been recorded in attacking a hawk that had entered their coop.[44]

If a chicken is threatened by predators, stress, or is sick, there is a chance that they will puff up their feathers.[39]

Reproduction

Sperm transfer occurs by cloacal contact between the male and female, in a maneuver known as the 'cloacal kiss'.[45] As with birds in general, reproduction is controlled by a neuroendocrine system, the Gonadotropin-Releasing Hormone-I neurons in the hypothalamus. Locally to the reproductive system itself, reproductive hormones such as estrogen, progesterone, gonadotropins (luteinizing hormone and follicle-stimulating hormone) initiate and maintain sexual maturation changes. Over time there is reproductive decline, thought to be due to GnRH-I-N decline. Because there is significant inter-individual variability in egg-producing duration, it is believed to be possible to breed for further extended useful lifetime in egg-layers.[46]

Embryology

(Video) Earliest gestation stages and blood circulation of a chicken embryo

Chicken embryos have long been used as model organisms to study developing embryos. Large numbers of embryos can be provided by commercial chicken farmers who sell fertilized eggs which can be easily opened and used to observe the developing embryo. Equally important, embryologists can carry out experiments on such embryos, close the egg again and study the effect later on. For instance, many important discoveries in the area of limb development have been made using chicken embryos, such as the discovery of the apical ectodermal ridge (AER) and the zone of polarizing activity (ZPA) by John W. Saunders.[47]

In 2006, scientists researching the ancestry of birds "turned on" a chicken recessive gene, talpid2, and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. John Fallon, the overseer of the project, stated that chickens have "...retained the ability to make teeth, under certain conditions... ."[48]

The G. gallus genome has 39 pairs of chromosomes, whereas the human genome contains 23 pairs
The G. gallus genome has 39 pairs of chromosomes, whereas the human genome contains 23 pairs

Genetics and genomics

Mottle gene
Mottle gene

Given its eminent role in farming, meat production, but also research, the house chicken was the first bird genome to be sequenced.[49] At 1.21 Gb, the chicken genome is considerably smaller than other vertebrate genomes, such as the human genome (3 Gb). The final gene set contained 26,640 genes (including noncoding genes and pseudogenes), with a total of 19,119 protein-coding genes in annotation release 103 (2017), a similar number of protein-coding genes as in the human genome.[50]

Physiology

Populations of chickens from high altitude regions like Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments. When eggs are placed in a hypoxic environment, chicken embryos from these populations express much more hemoglobin than embryos from other chicken populations. This hemoglobin also has a greater affinity for oxygen, allowing hemoglobin to bind to oxygen more readily.[51][52]

Pinopsins were originally discovered in the chicken pineal gland.[53]

Immunology

Although all avians appear to have lost TLR9, artificial immunity against bacterial pathogens has been induced in neonatal chicks by Taghavi et al. 2008 using tailored oligodeoxynucleotides.[54]

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Comb (anatomy)

Comb (anatomy)

A comb is a fleshy growth or crest on the top of the head of gallinaceous birds, such as turkeys, pheasants, and domestic chickens. Its alternative name cockscomb reflects that combs are generally larger on males than on females. There can be several fleshy protuberances on the heads and throats of gallinaceous birds, i.e. the comb, wattle, and earlobe, which collectively are called caruncles, however, in turkeys caruncle refers specifically to the fleshy nodules on the head and throat.

Omnivore

Omnivore

An omnivore is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutrients and energy of the sources absorbed. Often, they have the ability to incorporate food sources such as algae, fungi, and bacteria into their diet.

Lizard

Lizard

Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia although some lizards are more closely related to these two excluded groups than they are to other lizards. Lizards range in size from chameleons and geckos a few centimeters long to the 3-meter-long Komodo dragon.

Mouse

Mouse

A mouse is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse. Mice are also popular as pets. In some places, certain kinds of field mice are locally common. They are known to invade homes for food and shelter.

Breed

Breed

A breed is a specific group of domestic animals having homogeneous appearance (phenotype), homogeneous behavior, and/or other characteristics that distinguish it from other organisms of the same species. In literature, there exist several slightly deviating definitions. Breeds are formed through genetic isolation and either natural adaptation to the environment or selective breeding, or a combination of the two. Despite the centrality of the idea of "breeds" to animal husbandry and agriculture, no single, scientifically accepted definition of the term exists. A breed is therefore not an objective or biologically verifiable classification but is instead a term of art amongst groups of breeders who share a consensus around what qualities make some members of a given species members of a nameable subset.

Guinness World Records

Guinness World Records

Guinness World Records, known from its inception in 1955 until 1999 as The Guinness Book of Records and in previous United States editions as The Guinness Book of World Records, is a reference book published annually, listing world records both of human achievements and the extremes of the natural world. The brainchild of Sir Hugh Beaver, the book was co-founded by twin brothers Norris and Ross McWhirter in Fleet Street, London, in August 1955.

Caruncle (bird anatomy)

Caruncle (bird anatomy)

A caruncle is defined as 'a small, fleshy excrescence that is a normal part of an animal's anatomy'. Within this definition, caruncles in birds include wattles, combs, snoods, and earlobes. The term caruncle is derived from Latin caruncula, the diminutive of carō, "flesh".

Mutation

Mutation

In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitosis, or meiosis or other types of damage to DNA, which then may undergo error-prone repair, cause an error during other forms of repair, or cause an error during replication. Mutations may also result from insertion or deletion of segments of DNA due to mobile genetic elements.

Feather

Feather

Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier example of a complex evolutionary novelty. They are among the characteristics that distinguish the extant birds from other living groups.

Beard

Beard

A beard is the hair that grows on the jaw, chin, upper lip, lower lip, cheeks, and neck of humans and some non-human animals. In humans, usually pubescent or adult males are able to grow beards.

Empathy in chickens

Empathy in chickens

Empathy in chickens is the ability of a chicken to understand and share the feelings of another chicken. The Biotechnology and Biological Sciences Research Council's (BBSRC) Animal Welfare Initiative defines and recognizes that "...hens possess a fundamental capacity to empathise..." These empathetic responses in animals are well documented and are usually discussed along with issues related to cognition. The difference between animal cognition and animal emotion is recognized by ethicists. The specific emotional attribute of empathy in chickens has not been only investigated in terms of its existence but it has applications that have resulted in the designed reduction of stress in farm-raised poultry.

Herd

Herd

A herd is a social group of certain animals of the same species, either wild or domestic. The form of collective animal behavior associated with this is called herding.

Origin and dispersal

Origin

Male red junglefowl.
Male red junglefowl.

Galliformes, the order of bird that chickens belong to, is directly linked to the survival of birds when all other dinosaurs went extinct. Water or ground-dwelling fowl, similar to modern partridges, survived the Cretaceous–Paleogene extinction event that killed all tree-dwelling birds and dinosaurs.[55] Some of these evolved into the modern galliformes, of which domesticated chickens are a main model. They are descended primarily from the red junglefowl (Gallus gallus) and are scientifically classified as the same species.[56] As such, domesticated chickens can and do freely interbreed with populations of red junglefowl.[56] Subsequent hybridization of the domestic chicken with grey junglefowl, Sri Lankan junglefowl and green junglefowl occurred;[57] a gene for yellow skin, for instance, was incorporated into domestic birds through hybridization with the grey junglefowl (G. sonneratii).[58] In a study published in 2020, it was found that chickens shared between 71% - 79% of their genome with red junglefowl, with the period of domestication dated to 8,000 years ago.[57]

Red junglefowl hen in India
Red junglefowl hen in India

Domestication

In the last decade, there have been a number of genetic studies to clarify the origins. According to one early study, a single domestication event of the red junglefowl in what now is the country of Thailand gave rise to the modern chicken with minor transitions separating the modern breeds.[59] The red junglefowl, known as the bamboo fowl in many Southeast Asian languages, is well adapted to take advantage of the vast quantities of seed produced during the end of the multi-decade bamboo seeding cycle, to boost its own reproduction.[60] In domesticating the chicken, humans took advantage of this predisposition for prolific reproduction of the red junglefowl when exposed to large amounts of food.[61]

Exactly when and where the chicken was domesticated remains a controversial issue. Genomic studies estimate that the chicken was domesticated 8,000 years ago[57] in Southeast Asia and spread to China and India 2000–3000 years later. Archaeological evidence supports domestic chickens in Southeast Asia well before 6000 BC, China by 6000 BC and India by 2000 BC.[57][62][63] A landmark 2020 Nature study that fully sequenced 863 chickens across the world suggests that all domestic chickens originate from a single domestication event of red junglefowl whose present-day distribution is predominantly in southwestern China, northern Thailand and Myanmar. These domesticated chickens spread across Southeast and South Asia where they interbred with local wild species of junglefowl, forming genetically and geographically distinct groups. Analysis of the most popular commercial breed shows that the White Leghorn breed possesses a mosaic of divergent ancestries inherited from subspecies of red junglefowl.[64][65][66]

Dispersal

Middle Eastern chicken remains go back to a little earlier than 2000 BC in Syria; chickens went southward only in the 1st millennium BC. They reached Egypt for purposes of cockfighting about 1400 BC, and became widely bred only in Ptolemaic Egypt (about 300 BC).[67] Phoenicians spread chickens along the Mediterranean coasts as far as Iberia. During the Hellenistic period (4th–2nd centuries BC), in the Southern Levant, chickens began to be widely domesticated for food.[68] This change occurred at least 100 years before domestication of chickens spread to Europe.

Chickens reached Europe circa 100 BC.[69] Breeding increased under the Roman Empire, and was reduced in the Middle Ages.[67] Genetic sequencing of chicken bones from archaeological sites in Europe revealed that in the High Middle Ages chickens became less aggressive and began to lay eggs earlier in the breeding season.[70]

Three possible routes of introduction into Africa around the early first millennium AD could have been through the Egyptian Nile Valley, the East Africa Roman-Greek or Indian trade, or from Carthage and the Berbers, across the Sahara. The earliest known remains are from Mali, Nubia, East Coast, and South Africa and date back to the middle of the first millennium AD.[67]

Domestic chicken in the Americas before Western contact is still an ongoing discussion, but blue-egged chickens, found only in the Americas and Asia, suggest an Asian origin for early American chickens.[67]

A lack of data from Thailand, Russia, the Indian subcontinent, Southeast Asia and Sub-Saharan Africa makes it difficult to lay out a clear map of the spread of chickens in these areas; better description and genetic analysis of local breeds threatened by extinction may also help with research into this area.[67]

South America

An unusual variety of chicken that has its origins in South America is the Araucana, bred in southern Chile by the Mapuche people. Araucanas lay blue-green eggs. Additionally, some Araucanas are tailless, and some have tufts of feathers around their ears. It has long been suggested that they pre-date the arrival of European chickens brought by the Spanish and are evidence of pre-Columbian trans-Pacific contacts between Asian or Pacific Oceanic peoples, particularly the Polynesians, and South America. In 2007, an international team of researchers reported the results of their analysis of chicken bones found on the Arauco Peninsula in south-central Chile. Radiocarbon dating suggested that the chickens were pre-Columbian, and DNA analysis showed that they were related to prehistoric populations of chickens in Polynesia.[71] These results appeared to confirm that the chickens came from Polynesia and that there were transpacific contacts between Polynesia and South America before Columbus's arrival in the Americas.[72][73]

However, a later report looking at the same specimens concluded:

A published, apparently pre-Columbian, Chilean specimen and six pre-European Polynesian specimens also cluster with the same European/Indian subcontinental/Southeast Asian sequences, providing no support for a Polynesian introduction of chickens to South America. In contrast, sequences from two archaeological sites on Easter Island group with an uncommon haplogroup from Indonesia, Japan, and China and may represent a genetic signature of an early Polynesian dispersal. Modeling of the potential marine carbon contribution to the Chilean archaeological specimen casts further doubt on claims for pre-Columbian chickens, and definitive proof will require further analyses of ancient DNA sequences and radiocarbon and stable isotope data from archaeological excavations within both Chile and Polynesia.[74]

The debate for and against a Polynesian origin for South American chickens continued with this 2014 paper and subsequent responses in PNAS.[75]

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Galliformes

Galliformes

Galliformes is an order of heavy-bodied ground-feeding birds that includes turkeys, chickens, quail, and other landfowl. Gallinaceous birds, as they are called, are important in their ecosystems as seed dispersers and predators, and are often reared by humans for their meat and eggs, or hunted as game birds.

Order (biology)

Order (biology)

Order is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. An immediately higher rank, superorder, is sometimes added directly above order, with suborder directly beneath order. An order can also be defined as a group of related families.

Partridge

Partridge

A partridge is a medium-sized galliform bird in any of several genera, with a wide native distribution throughout parts of Europe, Asia and Africa. Several species have been introduced to the Americas. They are sometimes grouped in the Perdicinae subfamily of the Phasianidae. However, molecular research suggests that partridges are not a distinct taxon within the family Phasianidae, but that some species are closer to the pheasants, while others are closer to the junglefowl.

Cretaceous–Paleogene extinction event

Cretaceous–Paleogene extinction event

The Cretaceous–Paleogene (K–Pg) extinction event was a sudden mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 million years ago. With the exception of some ectothermic species such as sea turtles and crocodilians, no tetrapods weighing more than 25 kilograms survived. It marked the end of the Cretaceous Period, and with it the Mesozoic era, while heralding the beginning of the Cenozoic era, which continues to this day.

Grey junglefowl

Grey junglefowl

The gray junglefowl, also known as Sonnerat's junglefowl, is one of the wild ancestors of the domestic chicken together with the red junglefowl and other junglefowls.

Green junglefowl

Green junglefowl

The green junglefowl, also known as Javan junglefowl, forktail or green Javanese junglefowl, is the most distantly related and the first to diverge at least 4 million years ago among the four species of the junglefowl. Hybridization with domestic chicken has also been reported. Green junglefowl is a medium-sized bird in the pheasant family Phasianidae.

Egypt

Egypt

Egypt, officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Mediterranean Sea to the north, the Gaza Strip of Palestine and Israel to the northeast, the Red Sea to the east, Sudan to the south, and Libya to the west. The Gulf of Aqaba in the northeast separates Egypt from Jordan and Saudi Arabia. Cairo is the capital and largest city of Egypt, while Alexandria, the second-largest city, is an important industrial and tourist hub at the Mediterranean coast. At approximately 100 million inhabitants, Egypt is the 14th-most populated country in the world.

Ptolemy

Ptolemy

Claudius Ptolemy was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importance to later Byzantine, Islamic, and Western European science. The first is the astronomical treatise now known as the Almagest, although it was originally entitled the Mathēmatikē Syntaxis or Mathematical Treatise, and later known as The Greatest Treatise. The second is the Geography, which is a thorough discussion on maps and the geographic knowledge of the Greco-Roman world. The third is the astrological treatise in which he attempted to adapt horoscopic astrology to the Aristotelian natural philosophy of his day. This is sometimes known as the Apotelesmatika but more commonly known as the Tetrábiblos, from the Koine Greek meaning "Four Books", or by its Latin equivalent Quadripartite.

Hellenistic period

Hellenistic period

In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in 31 BC and the conquest of Ptolemaic Egypt the following year. The Ancient Greek word Hellas was gradually recognized as the name for Greece, from which the word Hellenistic was derived. "Hellenistic" is distinguished from "Hellenic" in that the latter refers to Greece itself, while the former encompasses all ancient territories under Greek influence, in particular the East after the conquests of Alexander the Great.

Middle Ages

Middle Ages

In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire and transitioned into the Renaissance and the Age of Discovery. The Middle Ages is the middle period of the three traditional divisions of Western history: classical antiquity, the medieval period, and the modern period. The medieval period is itself subdivided into the Early, High, and Late Middle Ages.

DNA sequencing

DNA sequencing

DNA sequencing is the process of determining the nucleic acid sequence – the order of nucleotides in DNA. It includes any method or technology that is used to determine the order of the four bases: adenine, guanine, cytosine, and thymine. The advent of rapid DNA sequencing methods has greatly accelerated biological and medical research and discovery.

High Middle Ages

High Middle Ages

The High Middle Ages, or High Medieval Period, was the period of European history that lasted from AD 1000 to 1300. The High Middle Ages were preceded by the Early Middle Ages and were followed by the Late Middle Ages, which ended around AD 1500.

Use by humans

Farming

A former battery hen, five days after release. Note the pale comb – the comb may be an indicator of health or vigor.[76]
A former battery hen, five days after release. Note the pale comb – the comb may be an indicator of health or vigor.[76]

More than 50 billion chickens are reared annually as a source of meat and eggs.[77] In the United States alone, more than 8 billion chickens are slaughtered each year for meat,[78] and more than 300 million chickens are reared for egg production.[79]

The vast majority of poultry are raised in factory farms. According to the Worldwatch Institute, 74 percent of the world's poultry meat and 68 percent of eggs are produced this way.[80] An alternative to intensive poultry farming is free-range farming.

Friction between these two main methods has led to long-term issues of ethical consumerism. Opponents of intensive farming argue that it harms the environment, creates human health risks and is inhumane.[81] Advocates of intensive farming say that their highly efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in state-of-the-art environmentally controlled facilities.[82]

Reared for meat

A commercial chicken house with open sides raising broiler pullets for meat
A commercial chicken house with open sides raising broiler pullets for meat

Chickens farmed for meat are called broilers. Chickens will naturally live for six or more years, but broiler breeds typically take less than six weeks to reach slaughter size.[83] A free range or organic broiler will usually be slaughtered at about 14 weeks of age.

Reared for eggs

Chickens farmed primarily for eggs are called layer hens. In total, the UK alone consumes more than 34 million eggs per day.[84] Some hen breeds can produce over 300 eggs per year, with "the highest authenticated rate of egg laying being 371 eggs in 364 days".[85] After 12 months of laying, the commercial hen's egg-laying ability starts to decline to the point where the flock is commercially unviable. Hens, particularly from battery cage systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from around seven years to less than two years.[86] In the UK and Europe, laying hens are then slaughtered and used in processed foods or sold as 'soup hens'.[86] In some other countries, flocks are sometimes force moulted, rather than being slaughtered, to re-invigorate egg-laying. This involves complete withdrawal of food (and sometimes water) for 7–14 days[87] or sufficiently long to cause a body weight loss of 25 to 35%,[88] or up to 28 days under experimental conditions.[89] This stimulates the hen to lose her feathers, but also re-invigorates egg-production. Some flocks may be force-moulted several times. In 2003, more than 75% of all flocks were moulted in the US.[90]

As pets

A 95-year-old woman from Havana, Cuba, with her pet rooster
A 95-year-old woman from Havana, Cuba, with her pet rooster

Keeping chickens as pets became increasingly popular in the 2000s[91] among urban and suburban residents.[92] Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs. Chickens provide companionship and have individual personalities. While many do not cuddle much, they will eat from one's hand, jump onto one's lap, respond to and follow their handlers, as well as show affection.[93][94]

Chickens are social, inquisitive, intelligent[95] birds, and many find their behaviour entertaining.[96] Certain breeds, such as Silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities.[97] Many people feed chickens in part with kitchen food scraps.

Backyard heritage chickens eating kitchen food scraps.
Backyard heritage chickens eating kitchen food scraps.

[98]

Cockfighting

Two cocks fighting
Two cocks fighting

A cockfight is a contest held in a ring called a cockpit between two cocks known as gamecocks. This term, denoting a cock kept for game, sport, pastime or entertainment, appears in 1646,[99] after "cock of the game" used by George Wilson in the earliest known book on the secular sport, The Commendation of Cocks and Cock Fighting of 1607. Gamecocks are not typical farm chickens. The cocks are specially bred and trained for increased stamina and strength. The comb and wattle are removed from a young gamecock because, if left intact, they would be a disadvantage during a match. This process is called dubbing. Sometimes the cocks are given drugs to increase their stamina or thicken their blood, which increases their chances of winning. Cockfighting is considered a traditional sporting event by some, and an example of animal cruelty by others and is therefore outlawed in most countries.[100] Usually wagers are made on the outcome of the match, with the survivor or last bird standing declared winner.

Chickens were originally used for cockfighting, a sport where 2 male chickens (cocks) fight each other until one dies or becomes badly injured. Cocks possess congenital aggression toward all other cocks to contest with females. Studies suggest that cockfights have existed even up to the Indus Valley civilisation as a pastime.[101] Today it is commonly associated with religious worship, pastime, and gambling in Asian and some South American countries. While not all fights are to the death, most use metal spurs as a weapon attached above or below the chicken's own spur, which typically results in death in one or both cocks. If chickens are in practice, owners place gloves on the spurs to prevent injuries. Cockfighting has been banned in most western countries and debated by animal rights activists for its brutality.

Artificial incubation

An egg incubator
An egg incubator

Incubation can occur artificially in machines that provide the correct, controlled environment for the developing chick.[102][103] The average incubation period for chickens is 21 days but the duration depends on the temperature and humidity in the incubator. Temperature regulation is the most critical factor for a successful hatch. Variations of more than 1 °C (1.8 °F) from the optimum temperature of 37.5 °C (99.5 °F) will reduce hatch rates. Humidity is also important because the rate at which eggs lose water by evaporation depends on the ambient relative humidity. Evaporation can be assessed by candling, to view the size of the air sac, or by measuring weight loss. Relative humidity should be increased to around 70% in the last three days of incubation to keep the membrane around the hatching chick from drying out after the chick cracks the shell. Lower humidity is usual in the first 18 days to ensure adequate evaporation. The position of the eggs in the incubator can also influence hatch rates. For best results, eggs should be placed with the pointed ends down and turned regularly (at least three times per day) until one to three days before hatching. If the eggs aren't turned, the embryo inside may stick to the shell and may hatch with physical defects. Adequate ventilation is necessary to provide the embryo with oxygen. Older eggs require increased ventilation.

Many commercial incubators are industrial-sized with shelves holding tens of thousands of eggs at a time, with rotation of the eggs a fully automated process. Home incubators are boxes holding from 6 to 75 eggs; they are usually electrically powered, but in the past some were heated with an oil or paraffin lamp.

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Poultry farming

Poultry farming

Poultry farming is the form of animal husbandry which raises domesticated birds such as chickens, ducks, turkeys and geese to produce meat or eggs for food. Poultry – mostly chickens – are farmed in great numbers. More than 60 billion chickens are killed for consumption annually. Chickens raised for eggs are known as layers, while chickens raised for meat are called broilers.

Chicken as food

Chicken as food

Chicken is the most common type of poultry in the world. Owing to the relative ease and low cost of raising chickens—in comparison to mammals such as cattle or hogs—chicken meat and chicken eggs have become prevalent in numerous cuisines.

Battery cage

Battery cage

Battery cages are a housing system used for various animal production methods, but primarily for egg-laying hens. The name arises from the arrangement of rows and columns of identical cages connected together, in a unit, as in an artillery battery. Although the term is usually applied to poultry farming, similar cage systems are used for other animals. Battery cages have generated controversy between advocates for animal welfare and industrial producers.

Intensive animal farming

Intensive animal farming

Intensive animal farming or industrial livestock production, also known by its opponents as factory farming and macro-farms, is a type of intensive agriculture, specifically an approach to animal husbandry designed to maximize production, while minimizing costs. To achieve this, agribusinesses keep livestock such as cattle, poultry, and fish at high stocking densities, at large scale, and using modern machinery, biotechnology, and global trade. The main products of this industry are meat, milk and eggs for human consumption. There are issues regarding whether intensive animal farming is sustainable in the social long-run given its costs in resources. Analysts also raise issues about its ethics.

Ethical consumerism

Ethical consumerism

Ethical consumerism is a type of consumer activism based on the concept of dollar voting. People practice it by buying ethically made products that support small-scale manufacturers or local artisans and protect animals and the environment, while boycotting products that exploit children as workers, are tested on animals, or damage the environment.

Intensive farming

Intensive farming

Intensive agriculture, also known as intensive farming, conventional, or industrial agriculture, is a type of agriculture, both of crop plants and of animals, with higher levels of input and output per unit of agricultural land area. It is characterized by a low fallow ratio, higher use of inputs such as capital and labour, and higher crop yields per unit land area.

Broiler

Broiler

A broiler is any chicken that is bred and raised specifically for meat production. Most commercial broilers reach slaughter weight between four and seven weeks of age, although slower growing breeds reach slaughter weight at approximately 14 weeks of age. Typical broilers have white feathers and yellowish skin. Broiler or sometimes broiler-fryer is also used sometimes to refer specifically to younger chickens under 2.0 kilograms, as compared with the larger roasters.

Free range

Free range

Free range denotes a method of farming husbandry where the animals, for at least part of the day, can roam freely outdoors, rather than being confined in an enclosure for 24 hours each day. On many farms, the outdoors ranging area is fenced, thereby technically making this an enclosure, however, free range systems usually offer the opportunity for the extensive locomotion and sunlight that is otherwise prevented by indoor housing systems. Free range may apply to meat, eggs or dairy farming.

Egg as food

Egg as food

Humans have eaten animal eggs for thousands of years. The most widely consumed eggs are those of fowl, especially chickens. Eggs of other birds, including ostriches and other ratites, are eaten regularly but much less commonly than those of chickens. People may also eat the eggs of reptiles, amphibians, and fish. Fish eggs consumed as food are known as roe or caviar.

List of chicken breeds

List of chicken breeds

There are hundreds of chicken breeds in existence. Domesticated for thousands of years, distinguishable breeds of chicken have been present since the combined factors of geographical isolation and selection for desired characteristics created regional types with distinct physical and behavioral traits passed on to their offspring.

Forced molting

Forced molting

Forced molting, sometimes known as induced molting, is the practice by some poultry industries of artificially provoking a flock to molt simultaneously, typically by withdrawing food for 7–14 days and sometimes also withdrawing water for an extended period. Forced molting is usually implemented when egg-production is naturally decreasing toward the end of the first egg-laying phase. During the forced molt, the birds cease producing eggs for at least two weeks, which allows the bird's reproductive tracts to regress and rejuvenate. After the molt, the hen's egg production rate usually peaks slightly lower than the previous peak, but egg quality is improved. The purpose of forced molting is therefore to increase egg production, egg quality, and profitability of flocks in their second or subsequent laying phases, by not allowing the hen's body the necessary time to rejuvenate during the natural cycle of feather replenishment.

Havana

Havana

Havana is the capital and largest city of Cuba. The heart of the La Habana Province, Havana is the country's main port and commercial center. The city has a population of 2.3 million inhabitants, and it spans a total of 728.26 km2 (281.18 sq mi) – making it the largest city by area, the most populous city, and the fourth largest metropolitan area in the Caribbean region.

Diseases and ailments

Chickens are susceptible to several parasites, including lice, mites, ticks, fleas, and intestinal worms, as well as other diseases. Despite the name, they are not affected by chickenpox, which is generally restricted to humans.[104]

Chickens can carry and transmit salmonella in their dander and feces. In the United States, the Centers for Disease Control and Prevention advise against bringing them indoors or letting small children handle them.[105][106]

Some of the diseases that can affect chickens are shown below:

Name Common name Cause
Aspergillosis Aspergillus fungi
Avian influenza bird flu virus
Histomoniasis blackhead disease Histomonas meleagridis
Botulism paralysis Clostridium botulinum toxin
Cage layer fatigue mineral deficiency, lack of physical exercise
Campylobacteriosis tissue injury in the gut
Coccidiosis Coccidia
Colds virus
Crop bound[107] improper feeding
Dermanyssus gallinae red mite parasite
Egg binding oversized egg
Erysipelas Streptococcus bacteria
Fatty liver hemorrhagic syndrome high-energy food
Fowl cholera Pasteurella multocida
Fowlpox Fowlpox virus
Fowl typhoid bacteria
Avian infectious laryngotracheitis LT Gallid alphaherpesvirus 1
Gapeworm Syngamus trachea worms
Infectious bronchitis[108] Infectious bronchitis virus
Infectious bursal disease Gumboro infectious bursal disease virus
Infectious coryza in chickens Avibacterium paragallinarum
Lymphoid leukosis Avian sarcoma leukosis virus
Marek's disease Gallid alphaherpesvirus 2
Moniliasis yeast infection
or thrush
Candida fungi
Mycoplasma bacteria
Newcastle disease Avian avulavirus 1
Necrotic enteritis[109] bacteria
Omphalitis Mushy chick disease[110] bacteria
Peritonitis[111] infection in abdomen from egg yolk
Psittacosis Chlamydia psittaci
Pullorum Salmonella bacteria
Scaly leg Knemidokoptes mutans
Squamous cell carcinoma cancer
Tibial dyschondroplasia speed growing
Toxoplasmosis Toxoplasma gondii
Ulcerative enteritis[112] bacteria
Ulcerative pododermatitis bumblefoot bacteria

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Mite

Mite

Mites are small arachnids. Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evidence of a close relationship.

Flea

Flea

Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about 3 millimetres long, are usually brown, and have bodies that are "flattened" sideways or narrow, enabling them to move through their hosts' fur or feathers. They lack wings; their hind legs are extremely well adapted for jumping. Their claws keep them from being dislodged, and their mouthparts are adapted for piercing skin and sucking blood. They can leap 50 times their body length, a feat second only to jumps made by another group of insects, the superfamily of froghoppers. Flea larvae are worm-like, with no limbs; they have chewing mouthparts and feed on organic debris left on their hosts' skin.

Chickenpox

Chickenpox

Chickenpox, also known as varicella, is a highly contagious disease caused by the initial infection with varicella zoster virus (VZV). The disease results in a characteristic skin rash that forms small, itchy blisters, which eventually scab over. It usually starts on the chest, back, and face. It then spreads to the rest of the body. The rash and other symptoms, such as fever, tiredness, and headaches, usually last five to seven days. Complications may occasionally include pneumonia, inflammation of the brain, and bacterial skin infections. The disease is usually more severe in adults than in children.

Centers for Disease Control and Prevention

Centers for Disease Control and Prevention

The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgia.

Aspergillosis

Aspergillosis

Aspergillosis is a fungal infection of usually the lungs, caused by the genus Aspergillus, a common mould that is breathed in frequently from the air around, but does not usually affect most people. It generally occurs in people with lung diseases such as asthma, cystic fibrosis or tuberculosis, or those who have had a stem cell or organ transplant, and those who cannot fight infection because of medications they take such as steroids and some cancer treatments. Rarely, it can affect skin.

Aspergillus

Aspergillus

Aspergillus is a genus consisting of several hundred mold species found in various climates worldwide.

Avian influenza

Avian influenza

Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds. The type with the greatest risk is highly pathogenic avian influenza (HPAI). Bird flu is similar to swine flu, dog flu, horse flu and human flu as an illness caused by strains of influenza viruses that have adapted to a specific host. Out of the three types of influenza viruses, influenza A virus is a zoonotic infection with a natural reservoir almost entirely in birds. Avian influenza, for most purposes, refers to the influenza A virus.

Histomoniasis

Histomoniasis

Histomoniasis is a commercially significant disease of poultry, particularly of chickens and turkeys, due to parasitic infection of a protozoan, Histomonas meleagridis. The protozoan is transmitted to the bird by the nematode parasite Heterakis gallinarum. H. meleagridis resides within the eggs of H. gallinarum, so birds ingest the parasites along with contaminated soil or food. Earthworms can also act as a paratenic host.

Histomonas meleagridis

Histomonas meleagridis

Histomonas meleagridis is a species of parasitic protozoan that infects a wide range of birds including chickens, turkeys, peafowl, quail and pheasants, causing infectious enterohepatitis, or histomoniasis. H. meleagridis can infect many birds, but it is most deadly in turkeys. It inhabits the lumen of cecum and parenchyma of liver, where it causes extensive necrosis. It is transmitted by another cecal parasite, the nematode Heterakis gallinarum.

Botulism

Botulism

Botulism is a rare and potentially fatal illness caused by a toxin produced by the bacterium Clostridium botulinum. The disease begins with weakness, blurred vision, feeling tired, and trouble speaking. This may then be followed by weakness of the arms, chest muscles, and legs. Vomiting, swelling of the abdomen, and diarrhea may also occur. The disease does not usually affect consciousness or cause a fever.

Clostridium botulinum

Clostridium botulinum

Clostridium botulinum is a Gram-positive, rod-shaped, anaerobic, spore-forming, motile bacterium with the ability to produce the neurotoxin botulinum.

Mineral deficiency

Mineral deficiency

Mineral deficiency is a lack of the dietary minerals, the micronutrients that are needed for an organism's proper health. The cause may be a poor diet, impaired uptake of the minerals that are consumed, or a dysfunction in the organism's use of the mineral after it is absorbed. These deficiencies can result in many disorders including anemia and goitre. Examples of mineral deficiency include, zinc deficiency, iron deficiency, and magnesium deficiency.

History

Two red junglefowl, a cock and a hen
Two red junglefowl, a cock and a hen

An early domestication of chickens in Southeast Asia is probable, since the word for domestic chicken (*manuk) is part of the reconstructed Proto-Austronesian language (see Austronesian languages). Chickens, together with dogs and pigs, were the domestic animals of the Lapita culture,[113] the first Neolithic culture of Oceania.[114]

The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BC.[115][116]

Chickens were spread by Polynesian seafarers and reached Easter Island in the 12th century AD, where they were the only domestic animal, with the possible exception of the Polynesian rat (Rattus exulans). They were housed in extremely solid chicken coops built from stone, which was first reported as such to Linton Palmer in 1868, who also "expressed his doubts about this".[117]

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Red junglefowl

Red junglefowl

The red junglefowl is a tropical bird in the family Phasianidae. It ranges across much of Southeast Asia and parts of South Asia. It was formerly known as the Bankiva or Bankiva Fowl. It is the species that gave rise to the chicken ; the grey junglefowl, Sri Lankan junglefowl and green junglefowl have also contributed genetic material to the gene pool of the chicken.

Proto-Austronesian language

Proto-Austronesian language

Proto-Austronesian is a proto-language. It is the reconstructed ancestor of the Austronesian languages, one of the world's major language families. Proto-Austronesian is assumed to have begun to diversify c. 3,500–4,000 BCE on Taiwan.

Austronesian languages

Austronesian languages

The Austronesian languages are a language family widely spoken throughout Maritime Southeast Asia, Madagascar, the islands of the Pacific Ocean and Taiwan. There are also a number of speakers in continental Asia. They are spoken by about 386 million people. This makes it the fifth-largest language family by number of speakers. Major Austronesian languages include Malay, Javanese, Sundanese, and Tagalog (Filipino). According to some estimates, the family contains 1,257 languages, which is the second most of any language family.

Neolithic

Neolithic

The Neolithic period, or New Stone Age, is an Old World archaeological period and the final division of the Stone Age. It saw the Neolithic Revolution, a wide-ranging set of developments that appear to have arisen independently in several parts of the world. This "Neolithic package" included the introduction of farming, domestication of animals, and change from a hunter-gatherer lifestyle to one of settlement.

Pottery

Pottery

Pottery is the process and the products of forming vessels and other objects with clay and other ceramic materials, which are fired at high temperatures to give them a hard and durable form. Major types include earthenware, stoneware and porcelain. The place where such wares are made by a potter is also called a pottery. The definition of pottery, used by the ASTM International, is "all fired ceramic wares that contain clay when formed, except technical, structural, and refractory products". In art history and archaeology, especially of ancient and prehistoric periods, "pottery" often means vessels only, and sculpted figurines of the same material are called "terracottas".

Polynesia

Polynesia

Polynesia is a subregion of Oceania, made up of more than 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are called Polynesians. They have many things in common, including language relatedness, cultural practices, and traditional beliefs. In centuries past, they had a strong shared tradition of sailing and using stars to navigate at night. The largest country in Polynesia is New Zealand.

Easter Island

Easter Island

Easter Island is an island and special territory of Chile in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian Triangle in Oceania. The island is most famous for its nearly 1,000 extant monumental statues, called moai, which were created by the early Rapa Nui people. In 1995, UNESCO named Easter Island a World Heritage Site, with much of the island protected within Rapa Nui National Park.

Polynesian rat

Polynesian rat

The Polynesian rat, Pacific rat or little rat, known to the Māori as kiore, is the third most widespread species of rat in the world behind the brown rat and black rat. The Polynesian rat originated in Southeast Asia, and like its relatives has become widespread, migrating to most of Polynesia, including New Zealand, Easter Island, and Hawaii. It shares high adaptability with other rat species extending to many environments, from grasslands to forests. It is also closely associated with humans, who provide easy access to food. It has become a major pest in most areas of its distribution.

Gallery

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Leghorn chicken

Leghorn chicken

The Leghorn is a breed of chicken originating in Tuscany, in central Italy. Birds were first exported to North America in 1828 from the Tuscan port city of Livorno, on the western coast of Italy. They were initially called "Italians", but by 1865 the breed was known as "Leghorn", the traditional anglicisation of "Livorno". The breed was introduced to Britain from the United States in 1870. White Leghorns are commonly used as layer chickens in many countries of the world. Other Leghorn varieties are less common.

Joseph Crawhall III

Joseph Crawhall III

Joseph Crawhall was an English artist born in Morpeth, Northumberland.

Orpington chicken

Orpington chicken

The Orpington is a British breed of chicken. It was bred in the late nineteenth century by William Cook of Orpington, Kent, in south-east England. It was intended to be a dual-purpose breed, to be reared both for eggs and for meat, but soon became exclusively a show bird.

Ontario

Ontario

Ontario is one of the thirteen provinces and territories of Canada. Located in Central Canada, it is Canada's most populous province, with 38.3 percent of the country's population, and is the second-largest province by total area. Ontario is Canada's fourth-largest jurisdiction in total area when the territories of the Northwest Territories and Nunavut are included. It is home to the nation's capital city, Ottawa, and the nation's most populous city, Toronto, which is Ontario's provincial capital.

Canada

Canada

Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over 9.98 million square kilometres, making it the world's second-largest country by total area. Its southern and western border with the United States, stretching 8,891 kilometres (5,525 mi), is the world's longest binational land border. Canada's capital is Ottawa, and its three largest metropolitan areas are Toronto, Montreal, and Vancouver.

Explanatory notes

  1. ^ The surgical and chemical castration of chickens is now illegal in some parts of the world.

Source: "Chicken", Wikipedia, Wikimedia Foundation, (2022, November 25th), https://en.wikipedia.org/wiki/Chicken.

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