Chicken Types, Characteristics & Uses

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. Large numbers of embryos can be provided commercially; fertilized eggs can easily be opened and used to observe the developing embryo. Keeping chickens as pets became increasingly popular in the 2000s among urban and suburban residents.

Social hierarchy

In groups of male chicks, however, fights for dominance may continue into adulthood. The pecking order is established within groups of female chicks by the 10th week of life. The time between ovulation and egg-laying is approximately 23–26 hours.

• Sperm transfer occurs by cloacal contact between the male and female, in an action called the ‘cloacal kiss’.
• 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.
• 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.

Farming

Genomic studies estimated that the chicken was domesticated 8,000 years ago in Southeast Asia and spread to China and India 2,000 to 3,000 years later. Fertile chicken eggs hatch at the end of the incubation period, about 21 days; the chick uses its egg tooth to break out of the shell. The concept of dominance, involving pecking, was described in female chickens by Thorleif Schjelderup-Ebbe in 1921 as the “pecking order”. Individual chickens dominate others, establishing a pecking order; dominant individuals take priority for access to food and nest sites. Chickens are primarily kept for their meat and eggs, though they are also kept as pets. In situations where one adult bird challenges another—which happens most often when a new bird is introduced into the flock—fights involving males risk injury and death more often than fights involving females.

Egg laying is stimulated by the long stretches of daylight that occur during the warmer months; however, artificial lights placed in chicken coops can trigger a hen’s egg laying response throughout the year. Males (called cocks or roosters) and females (hens) are known for their fleshy combs, lobed wattles hanging below the bill, and high-arched tails. In the process of domestication, chickens were apparently kept initially for cockfighting, and only later used khela 88 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.

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. A flock thus uses only a few preferred locations, rather than having a different nest for every bird. Reproduction declines with age, thought to be due to a decline in GnRH-I-N. If the female is unreceptive, she runs off; otherwise, she crouches, and the male mounts, treading with both feet on her back.