Chicken

The chicken (Gallus gallus domesticus) is a type of bird that people have kept for a very long time. It comes from the red junglefowl and was first kept by humans in Southeast Asia about 8,000 years ago. Today, chickens are one of the most common domesticated animals in the world.

People keep chickens mainly for their meat and eggs. Some people also keep them as pets.

Chickens are social birds. They make many different sounds and have interesting behaviors. Chickens appear in stories, traditions, and writings in many places around the world. They are very important for farming and are a big part of animal husbandry.

Etymology

The word chicken comes from an old English word, cicen. It has German roots, but we are not sure where the word came from. It might have come from trying to copy the sound a chicken makes.

Nomenclature

Here are some common words for chickens:

• Biddy: a chicken or a newly hatched chicken
• Capon: a male chicken that has been neutered
• Chick: a young chicken
• Chook: a chicken (used in Australia and New Zealand)
• Cock: a fertile adult male chicken
• Cockerel: a young male chicken
• Hen: an adult female chicken
• Pullet: a young female chicken less than a year old
• Rooster: a fertile adult male chicken, especially in North America
• Yardbird: a chicken (used in some parts of the southern United States)

The word "chicken" can also mean a young chick. This is how the word was used long ago, like in a play by William Shakespeare called Macbeth. It is still seen in place names such as the Hen and Chicken Islands. Sometimes chickens are called "common fowl" or "domestic fowl".

Description

Chickens are large birds that are active during the day. They have round bodies, unfeathered legs, and short wings. Unlike their wild relatives, chickens cannot fly far because they are too heavy. Their size and colors vary a lot between types. Baby chicks weigh about 37 g when they hatch, but modern chickens grow faster than older types.

Both male and female chickens have a special fleshy crest on their heads called a comb and flaps of skin under their beaks called wattles. These are usually bigger on males. Some chickens even have extra feathers under their faces, giving them a bearded look. Chickens eat many things, searching the ground for seeds, insects, and small animals. They can live between 5 to 10 years, depending on their type. Chickens live in groups and take turns getting food and nesting spots. They make different sounds to talk to each other and warn of danger.

Reproduction and life-cycle

Some roosters may dance around a hen to show interest. If she responds, they mate. After mating, the male shows a special display with his tail.

Sperm transfer happens through a special contact called the 'cloacal kiss'. Like all birds, chickens control their reproduction through a special system in their brains. Hormones help start and keep the changes for reproduction.

Hens often try to lay eggs in nests that already have eggs and may move eggs from other nests into their own. A flock usually uses just a few favorite spots for nesting. In natural conditions, most hens lay eggs until their clutch is complete, then they sit on the nest to keep the eggs warm until they hatch. This is called going broody.

Chickens from high-altitude areas in Tibet have special adaptations in their eggs that help them hatch better in low oxygen areas. When placed in such environments, the embryos in these eggs produce more hemoglobin, which helps them get oxygen more easily.

Fertile chicken eggs hatch after about 21 days. The chick uses a small bump called an egg tooth to break out of the shell. After hatching, the hen stays close to her chicks for about two days. During this time, the chicks feed by absorbing an internal yolk sac. The hen protects her chicks, keeps them warm, and leads them to food and water. The chicks quickly learn to follow the hen. She continues to care for them until they are several weeks old.

Origin

Chickens are birds that are related to modern partridges. They belong to the Galliformes order of birds. Chickens survived a big event called the Cretaceous–Paleogene extinction event.

They come mostly from the red junglefowl (Gallus gallus). Domesticated chickens can breed with red junglefowl.

Further information: Domestication

The red junglefowl likes to eat seeds, especially when many seeds grow at once during the multi-decade bamboo seeding cycle. People noticed that red junglefowl have lots of babies when there is lots of food.

Scientists think people started keeping chickens about 8,000 years ago in Southeast Asia. They later spread to China and India. Early evidence of chickens has been found in Southeast Asia before 6000 BC, in China by 6000 BC and India by 2000 BC. Studies show that all chickens likely came from one group of red junglefowl in Southeast Asia. These chickens then spread and mixed with local wild birds.

Bones found at many sites show that the earliest chickens lived about 3,250 years ago in Thailand, at Ban Non Wat. Some scientists think that wild birds were attracted to rice fields, nested nearby, and became domesticated chickens. Bones of these birds were found in graves, showing they were kept by people.

Dispersal

Austronesia

The word for chickens in old languages shows that people raised them a very long time ago. Chickens traveled with people across many islands and places, starting around 3000 BC from Taiwan. They may have reached South America long ago, but we are not sure.

Africa

Chickens came to Egypt from the Middle East around 1400 BC and were raised there by about 300 BC. They spread to Africa through many paths, including trade and travel.

Americas

Some researchers think chickens might have been in the Americas before Europeans came, based on special blue-egged chickens found there and in Asia. But we do not have enough information to be sure, and more study is needed.

Eurasia

Finding the age of chicken bones is hard because they are small and break easily. There are clues from old writings and art that show chickens were common in places like Central Asia by the 4th century BC. Chickens were in the Middle East before 2000 BC and spread around the Mediterranean by people from Syria. By the time of the Roman Empire, raising chickens became more common.

Diseases

Main article: Poultry disease

Chickens can get sick from tiny creatures called parasites like mites. They can also catch diseases caused by tiny living things called pathogens, such as bacteria and viruses. One parasite, Dermanyssus gallinae, feeds on the chicken’s blood. This can bother the chicken and make it lay fewer eggs. The parasite can also spread some diseases like salmonellosis and spirochaetosis. There are also viral diseases, such as avian influenza.

Use by humans

Main article: Poultry farming

Chickens are common animals that people keep on farms. Many chickens are raised for their meat and eggs. Some chickens live on special farms, while others are kept on farms where they can move around more freely.

Keeping chickens as pets is popular, especially in cities and towns. People enjoy their company and find them intelligent and fun. Chickens can be friendly and gentle, making them good pets for children.

Main article: Cockfight

Chickens have been used in science to study how animals grow. Their eggs help scientists learn about body parts.

Main article: Cultural references to chickens

Chickens appear in many stories, traditions, and artworks. They are important in some religions and cultures and have inspired art and literature. Chickens are also featured in movies and nursery rhymes.

See also: Chicken as biological research model and Shell-less chick embryo culture