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A chicken (Gallus gallus domesticus) is a type of domesticated bird which is often raised as a type of poultry. It is believed to be descended from the wild Indian and south-east Asian Red Junglefowl. With a population of more than 24 billion in 2003 (according to the Firefly Encyclopedia of Birds), there are more chickens in the world than any other bird. They provide two sources of food frequently consumed by humans: their meat, also known as chicken, and eggs.
General biology and habitat Male chickens are known as roosters (in the U.S., Canada and Australia), cocks, or cockerels if they are young. Female chickens are known as hens, or 'chooks' in Australasian English. Young females 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. However, in some breeds, such as the Sebright, the cock only has slightly pointed neck feathers, and the identification must be made by looking at the comb. Chickens have a fleshy crest on their heads called a comb, and a fleshy piece of hanging skin under their beak called a wattle. These organs help to cool the bird by redirecting bloodflow to the skin. Both the male and female have distinctive wattles and combs. In males, the combs are often more prominent, though this is not the case in all varieties. Domestic chickens are typically fed commercially prepared feed that includes a protein source as well as grains. Chickens often scratch at the soil to get at adult insects and larvae or seed. Incidents of cannibalism can occur when a curious bird pecks at a pre-existing wound or during fighting (even among female birds). This is exacerbated in close quarters. In commercial egg production this is controlled by trimming the beak (removal of ⅔ of the top half and occasionally ⅓ of the lower half of the beak). Domestic chickens are not capable of flying for long distances, although they are generally capable of flying for short distances such as over fences. Chickens will sometimes fly simply in order to explore their surroundings, but will especially fly in an attempt to flee when they perceive danger. Because of the risk of flight, chickens raised in the open air 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 (more on wing clipping). 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. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Chickens will try to lay in nests that already contain eggs, and have been known to move eggs from neighbouring nests into their own. Some farmers use fake eggs made from plastic or stone to encourage hens to lay in a particular location. 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. Hens can also 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 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. Chickens are domesticated descendants of the red junglefowl, which is biologically classified as the same species. Recent studies * have shown that chickens (and possibly other bird species) still retain the genetic blueprints to produce teeth in the jaws, although these are dormant in living animals. These are a holdover from primitive birds such as Archaeopteryx, which were descended from theropod dinosaurs. Courting 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. Going broody 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 broody, the hen keeps the eggs at a 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 hear the chicks peeping inside the eggs, and will gently cluck to encourage them to break out of their shells. If the eggs are not fertilized and do not hatch, the hen will eventually grow tired of being broody 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 mothers. Artificial incubation Chicken egg incubation can successfully occur artificially as well. Nearly all chicken eggs will hatch after 21 days of good conditions - 99.5° fahrenheit (37.5°C) and around 55% relative humidity (increase to 70% in the last three days of incubation to help soften egg shell). 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 usually small boxes (styrofoam incubators are popular) and hold a few to 50 eggs. Eggs must be turned three to five times each day, rotating at least 90 degrees. If eggs aren't turned, the embryo inside will stick to the shell and likely will be hatched with physical defects. This process is natural; hens will stand up three to five times a day and shift the eggs around with their beak. Chickens as food
Chickens as pets
Chickens in agriculture In the United States, chickens were once raised primarily on family farms. Prior to about 1930, chicken was served primarily on special occasions or on Sunday, as the birds were typically more valued for their eggs than meat. Excess roosters or non-productive hens would be culled from the flock first for butchering. As cities developed and markets sprung up across the nation, live chickens from local farms could often be seen for sale in crates outside the market to be butchered and cleaned onsite by the butcher. With the advent of vertical integration and selective breeding of efficient meat-type birds, poultry production changed dramatically. Large farms and packing plants emerged that could grow birds by the thousands. Chickens could be sent to slaughterhouses for butchering and processing into pre-packaged commercial products to be frozen or shipped fresh to markets or wholesalers. Meat-type chickens currently grow to market weight in 6-7 weeks whereas only fifty years ago it took three times as long (reference: Havenstein, G.B., P.R. Ferket, and M.A. Qureshi, 2003a. Growth, livability, and feed conversion of 1957 versus 2001 broilers when feed representative 1957 and 2001 broiler diets. Poult. Sci. 82:1500-1508). This is due exclusively to genetic selection and nutritional advances (and not to use of growth hormones, which are illegal for use in poultry in the US and many other countries). Once a meat consumed only occasionally, the common availability and lower cost has made chicken a common and significant 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. Another breed of chicken, the Leghorn, was further developed to be efficient layers of eggs. Egg production and consumption changed with the development of automation and refrigeration. Large farms were devoted solely to egg production and packaging. Today, eggs are produced on large egg ranches on which environmental parameters are well controlled. Chickens are exposed to artificial light cycles to stimulate egg production year-round. In addition, it is a common practice to induce molt through careful 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, however this varies from breed to time of year. For example, a Barred Plymouth Rock may lay one egg a day, during the spring, summer and fall. But the same chicken may not lay at all during the winter. However, a chicken bred specifically for egg-laying may occasionally lay two eggs a day, and if housed correctly may lay all through the winter. Often, people in developing countries keep chickens for their eggs and meat. Issues with mass production Many animal rights advocates object to killing chickens for food or to the "factory farm conditions" under which they are raised. They contend that commercial chicken production often involves raising the birds in large, crowded rearing sheds that prevent the chickens from engaging in many of their natural behaviors. Contrary to popular belief, however, meat-type chickens are not raised in cages and are instead raised on the floor on litter such as rice hulls. They are slaughtered prior to sexual maturity, and thus many of the aggressive behaviors seen in adult chickens (fighting, cannibalism) are seldom seen in meat-type chickens. In 2004, 8.9 billion chickens were slaughtered in the United States*. Although many would argue that the birds are not intelligent and thus not a high priority for humane treatment on farms, a woman once brought a chicken on The Tonight Show with Jay Leno where it played "Mary Had A Little Lamb" on a toy piano and bowled 3 strikes. Animal rights groups such as PETA see this and other "amazing" trained chickens as evidence that they are intelligent and sentient and should not be killed or eaten *. Another animal welfare issue 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. In addition, many scientists have raised concerns that companies growing one variety of bird for eggs or meat are causing them to become much more susceptible to disease. For this reason, many scientists are promoting the conservation of heritage breeds to retain genetic diversity in the species. Chicken diseases Chickens are susceptible to parasites, including lice, mites, ticks, fleas, and intestinal Worms as well as many other deseases. (Despite the name, they are not affected by Chickenpox; it is a disease of humans, not chickens.) Some of the common deseases that affect chickens are shown below: Chickens in religion
History The first pictures of chickens in Europe are found on Corinthian pottery of the 7th century BC. The poet Cratinus (mid-5th century BC, according to the later Greek author Athenaeus) calls the chicken "the Persian alarm". In Aristophanes's comedy The Birds (414 BC) 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. In ancient Greece, chickens were still rare and were a rather prestigious food for symposia. Delos seems to have been a centre of chicken breeding. An early domestication of chickens in Southeast Asia is probable, since the word for domestic chicken ( 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. Traveling as cargo on trading boats, they reached the Asian continent via the islands of Indonesia and from there spread west to Europe and western Asia. Chickens in ancient Rome The Romans used chickens for oracles, both when flying ("ex avibus") and when feeding ("auspicium ex tripudiis"). The hen ("gallina") gave a favourable 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 BC, 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 161 BC a law was passed in Rome that forbade the consumption of fattened chickens. It was renewed a number of times, but does not seem to have been successful. Fattening chickens with bread soaked in milk was thought to give especially delicious results. The Roman gourmet Apicius offers 17 recipes for chicken, mainly boiled chicken with a sauce. All parts of the animal are used: the recipes include the stomach, liver, testicles and even the pygostyle (the fatty "tail" of the chicken where the tail feathers attach). The Roman author Columella gives advice on chicken breeding in his eighth book of his treatise on agriculture. He identifies Tanagrian, Rhodic, Chalkidic and Median (commonly misidentified as Melian) breeds, which have an impressive appearance, a quarrelsome nature and were used for cockfighting by the Greeks. For farming, native (Roman) chickens are to be preferred, or a cross between native hens and Greek cocks. Dwarf chickens are nice to watch because of their size but have no other advantages. Per Columella, the ideal flock consists of 200 birds, which can be supervised by one person if someone is watching for stray animals. White chickens should be avoided as they are not very fertile and are easily caught by eagles or goshawks. One cock should be kept for five hens. In the case of Rhodian and Median cocks that are very heavy and therefore not much inclined to sex, only three hens are kept per cock. The hens of heavy fowls are not much inclined to brood; therefore their eggs are best hatched by normal hens. A hen can hatch no more than 15-23 eggs, depending on the time of year, and supervise no more than 30 hatchlings. Eggs that are long and pointed give more male, rounded eggs mainly female hatchlings. Per Columella, Chicken coops should face southeast and lie adjacent to the kitchen, as smoke is beneficial for the animals. Coops should consist of three rooms and possess a hearth. Dry dust or ash should be provided for dust-baths. According to Columella, chicken should be fed on barley groats, small chick-peas, millet and wheat bran, if they are cheap. Wheat itself should be avoided as it is harmful to the birds. Boiled ryegrass (Lollium sp.) and the leaves and seeds of alfalfa (Medicago sativa L.) can be used as well. Grape marc can be used, but only when the hens stop laying eggs, that is, about the middle of November; otherwise eggs are small and few. When feeding grape marc, it should be supplemented with some bran. Hens start to lay eggs after the winter solstice, in warm places around the first of January, in colder areas in the middle of February. Parboiled barley increases their fertility; this should be mixed with alfalfa leaves and seeds, or vetches or millet if alfalfa is not at hand. Free-ranging chickens should receive two cups of barley daily. Columella advises farmers to slaughter hens that are older than three years, because they no longer produce sufficient eggs. Capons were produced by burning out their spurs with a hot iron. The wound was treated with potter's chalk. For the use of poultry and eggs in the kitchens of ancient Rome see Roman eating and drinking. Chicken Breeds Real chickens Fictional chickens Mythical creatures with chicken-like anatomy Chicken as symbol See also | |||||||||||||||||||||||||||||||||||||||||||
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