Chicken Types, Characteristics & Uses

As with all birds, reproduction is controlled by a neuroendocrine system, the Gonadotropin-Releasing Hormone-I neurons in the hypothalamus. Chickens have been thought of primarily as providers of food, but their cognition, emotions, and sociality are comparable with other birds and mammals. 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.

Inbreeding of White Leghorn chickens tends to cause inbreeding depression expressed as reduced egg number and delayed sexual maturity. When eggs are placed in a hypoxic environment, chicken embryos from these populations express much more hemoglobin than embryos from other chicken populations. Adult chickens of both sexes have a fleshy crest on their heads called a comb or cockscomb, and hanging flaps of skin on either side under their beaks called wattles; combs and wattles are more prominent in males. Wild junglefowl can fly, whereas domestic chickens and their flight muscles are too heavy to allow them to fly more than a short distance. Defrost the chicken in the fridge (it can take around 2 days), then allow it to stand uncovered out of the fridge for no more than half an hour before cooking.

Domestication

This stimulates the hen to lose her feathers but also re-invigorates egg-production. In some other countries, flocks are sometimes force-moulted rather than being slaughtered to re-invigorate egg-laying. After 12 months of laying, the commercial hen’s egg-laying ability declines to the point where the flock is commercially unviable.

• Chickens are social, inquisitive, intelligent birds, and many people find their behaviour entertaining.
• The domestic chicken has subsequently hybridised with grey junglefowl, Sri Lankan junglefowl and green junglefowl; a gene for yellow skin, for instance, was incorporated into domestic birds from the grey junglefowl (G. sonneratii).
• 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.
• Middle Eastern chicken remains go back to a little earlier than 2000 BC in Syria.
• Chickens give different warning calls to indicate that a predator is approaching from the air or on the ground.

Africa

The chicks imprint on the hen and subsequently follow her continually. Eggs of chickens from the high-altitude region of Tibet have special physiological adaptations that result in a higher hatching rate in low oxygen environments. A flock thus uses only a few preferred locations, rather than having a different nest for every bird. Hens often try to lay in nests that already contain eggs and sometimes move eggs from neighbouring nests into their own. Sperm transfer occurs by cloacal contact between the male and female, in an action called the ‘cloacal kiss’.

Certain breeds, such as silkies and many bantam varieties, are generally docile and are often recommended as good pets around children with disabilities. This involves complete withdrawal of food (and sometimes water) for 7–14 days or sufficiently long to cause a body weight loss of 25 to 35%, or up to 28 days under experimental conditions. Hens, particularly from battery cage systems, are sometimes infirm or have lost a significant amount of their feathers, and their life expectancy has been reduced from mostly play around seven years to less than two years. Broiler breeds typically take less than six weeks to reach slaughter size, some weeks longer for free-range and organic broilers. Advocates of intensive farming say that their efficient systems save land and food resources owing to increased productivity, and that the animals are looked after in a controlled environment.