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Chicken

life science Maturity 9-11 Vital Level 3 Next article →

The chicken, known scientifically as Gallus gallus domesticus, is a highly successful domesticated bird. It is a widespread species found in almost every part of the world. Most people keep chickens for their meat or their eggs. Some people also keep them as pets. As of 2023, the global chicken population is over 26.5 billion birds.

chicken meat production, World, 2023 (cropped)
chicken meat production, World, 2023 (cropped)

Every year, more than 50 billion birds are produced for human consumption. This makes chickens a central part of global animal husbandry, which is the science of raising livestock.

Chickens are descended from the red junglefowl, or Gallus gallus. These wild birds are native to Southeast Asia.

Red Junglefowl
Red Junglefowl

Scientists believe the two are the same species. Domestic chickens have also interbred with other types, such as the grey, green, and Sri Lankan junglefowl. For example, a gene for yellow skin came from the grey junglefowl. Modern chickens share between 71% and 79% of their genome with the red junglefowl. This means their genetic makeup is very similar to their wild ancestors.

Humans began domesticating chickens roughly 8,000 years ago in Southeast Asia.

Chicken domestication and dispersal
Chicken domestication and dispersal

One theory suggests this happened alongside the growth of rice. In central Thailand, at a site called Ban Non Wat, researchers found chicken bones from 3,250 years ago. They believe wild junglefowl were attracted to the rice seeds. The birds nested near the crops and eventually became tame. From Southeast Asia, chickens spread to China and India. They later reached Africa and the Americas through various trade routes and migrations.

Chickens have many different names based on their age and sex. An adult female is a hen. A young female under one year old is a pullet. In the poultry industry, a pullet is considered sexually immature if it is under 22 weeks of age. An adult male is a cock or a rooster. A young male is a cockerel.

A Barred Rock Chicken Named Rootrip
A Barred Rock Chicken Named Rootrip

Newly hatched birds are called chicks or biddies. There are also specialized breeds. Broilers are chickens bred specifically for meat. Laying hens are bred to produce eggs. A single laying hen can produce over 300 eggs in one year.

Physically, chickens are large, active birds that are most busy during the day. They have round bodies and short wings. Because their flight muscles are quite heavy, they can only fly short distances. Most breeds have unfeathered legs. Both males and females have a fleshy crest on their heads called a comb. They also have skin flaps under their beaks called wattles. These features are usually more prominent on males. Some breeds even have extra feathers under their faces that look like a beard.

Chickens are social animals that live in groups called flocks. They follow a social structure known as a pecking order. This was described by Thorleif Schjelderup-Ebbe in 1921. In this system, certain individuals are dominant. These dominant birds get first access to food and the best nesting sites. Chickens also use complex vocalizations to communicate. Roosters use a loud crow to signal their territory. Hens cluck to call their chicks or to signal after laying an egg. They even have different warning calls for predators on the ground versus those in the air.

Reproduction in chickens is controlled by a neuroendocrine system. This involves hormones like estrogen and progesterone.

Newly-hatched chickens
Newly-hatched chickens

To mate, a rooster may perform a circle dance near a hen. If the hen is receptive, the male mounts her. Sperm transfer happens through a process called the "cloacal kiss." After mating, the hen may go "broody." This means she sits on a nest to incubate her eggs. The incubation period lasts about 21 days. When the chicks hatch, they use a tiny egg tooth to break the shell. The hen then protects and warms them as they learn to feed.

Chickens are omnivores, meaning they eat both plants and animals. In the wild, they scratch the soil for seeds and insects. They may even eat small animals like lizards, snakes, or mice. While they are often seen as food sources, they are very intelligent. Their emotions and social behaviors are similar to other birds and mammals. They can even work together to mob and kill a predator, such as a young fox.

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🖼️ Images & Media (9)
Rooster crowing small.ogv
File:Newly-hatched chickens.jpg
Newly-hatched chickens.jpg
File:Red Junglefowl.jpg
Red Junglefowl.jpg
File:Chicken domestication and dispersal.svg
Chicken domestication and dispersal.svg
File:Map showing prehistoric diffusion of domestic chickens (Gallus gallus) into the Pacific via the Austronesian migrations (Thomson, Lebrasseur, & Austin, 2014).png
Map showing prehistoric diffusion of...
File:A Barred Rock Chicken Named Rootrip.png
A Barred Rock Chicken Named Rootrip.png
File:Pesse oujheas H9N2 tanfla.JPG
Pesse oujheas H9N2 tanfla.JPG
File:chicken meat production, World, 2023 (cropped).svg
chicken meat production, World, 2023 (cropped).svg
File:COCK FIGHT.JPG
COCK FIGHT.JPG
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