CHICKEN中文繁體翻譯：劍橋詞典

For most of that period, chickens were a common part of the livestock complement of farms and ranches throughout Eurasia and Africa. Each flock of chickens develops a social hierarchy that determines access to food, nesting sites, mates, and other resources. In 2006, scientists researching the ancestry of birds switched on a chicken recessive gene, talpid2, and found that the embryo jaws initiated formation of teeth, like those found in ancient bird fossils. This stimulates the hen to lose her feathers but also re-invigorates egg-production.

• The hen can hear the chicks peeping inside the eggs, and will gently cluck to encourage them to break out of their shells.
• Chickens will sometimes attempt flight simply to explore their surroundings, however, they will especially fly in an attempt to flee when they perceive danger or pursued by a predator.
• Domesticated chickens freely interbreed with populations of red junglefowl.
• This stimulates the hen to lose her feathers but also re-invigorates egg-production.

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Despite the chicken’s close relationship with the red jungle fowl, there is evidence that the gray jungle fowl (G. sonneratii) of southern India and other jungle fowl species, also members of Gallus, may have contributed to the bird’s ancestry. In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used for food. Many people obtain chickens for their egg production but often name them and treat them as any other pet like cats or dogs. 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. The possibility that domestic chickens were in the Americas before Western contact is debated by researchers, but blue-egged chickens, found only in the Americas and Asia, suggest an Asian origin for early American chickens.

In the wild, they scratch at the soil to search for seeds, insects, and animals as large as lizards, small snakes, and young mice. Some breeds have a mutation that causes extra feathering under the face, giving the appearance of a beard. Modern varieties however grow much faster; by day 35 a Ross 708 broiler may weigh 1.8 kg (4.0 lb) as against the 1.05 kg (2.3 lb) of a heritage chicken of the same age. Newly hatched chicks of both modern and heritage varieties weigh the same, about 37 g (1.3 oz).

Specialized breeds such as broilers and laying hens have been developed for meat and egg production, respectively. In the United States alone, more than 8 billion chickens are slaughtered each year for meat, and more than 300 million chickens are reared for egg production. More than 50 billion chickens are reared annually as a source of meat and eggs.

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Hens remain on the nest for about two days after the first chick hatches; during this time the newly hatched chicks feed by absorbing the internal yolk sac. The hen sits on the nest, fluffing up or pecking defensively if disturbed. Reproduction declines with age, thought to be due to a decline in GnRH-I-N.

Domestication

Besides humans, lots of animals eat chickens as well. Modern egg-laying breeds rarely go broody and those that do often stop part-way through the incubation cycle. 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. Individual chickens in a flock will dominate others, establishing a ‘pecking order’, with dominant individuals having priority for access to food and nesting locations. Domestic chickens are typically fed commercially prepared feed that includes a protein source as well as grains. Chickens can be kept as pets, for breeding, egg laying and a food product.

All the time she is sitting in the nest she will regularly turn the eggs keeping them at a constant temperature and humidity. When a hen becomes familiar coming to his ‘call’ the rooster may mate with the hen and fertilize her egg. Removing hens or krikya-online.com roosters from a flock causes a temporary disruption to this social order until a new pecking order is established. Chickens have a communal approach to the incubation of eggs and raising of young. Chickens are gregarious birds and live together as a flock.