Monday, February 26, 2007

General biology and habitat

Male chickens are known as roosters (in the U.S., Canada and Australia), cocks, or cockerels. Castrated roosters are called capons. Female chickens are known as hens, or 'chooks' in Australian English. Young females are known as pullets. Roosters can usually be differentiated from hens by their striking plumage, marked by long flowing tails and bright pointed feathers on their necks.

However, in some breeds, such as the Sebright, the cock only has slightly pointed neck feathers, and the identification must be made by looking at the comb. Chickens have a fleshy crest on their heads called a comb or cockscomb, and a fleshy piece of hanging skin under their beak called a wattle. These organs help to cool the bird by redirecting blood flow to the skin. Both the male and female have distinctive wattles and combs. In males, the combs are often more prominent, though this is not the case in all varieties.

Domestic chickens are typically fed commercially prepared feed that includes a protein source as well as grains. Chickens often scratch at the soil to get at adult insects and larvae or seed. Incidents of cannibalism can occur when a curious bird pecks at a preexisting wound or during fighting (even among female birds). This is exacerbated in close quarters. In commercial egg and meat production this is controlled by trimming the beak (removal of ⅔ of the top half and occasionally ⅓ of the lower half of the beak).

Domestic chickens are not capable of long distance flight, although they are generally capable of flying for short distances such as over fences. Chickens will sometimes fly to explore their surroundings, but usually only to flee perceived danger. Because of flight risk, chickens raised in open-air pens generally have one of their wings clipped by the breeder — the tips of the longest feathers on one of the wings are cut, resulting in unbalanced flight which the bird cannot sustain for more than a few meters (more on wing clipping).

Chickens are gregarious birds and live together as a flock. They have a communal approach to the incubation of eggs and raising of 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. Removing hens or roosters from a flock causes a temporary disruption to this social order until a new pecking order is established.

Chickens will try to lay in nests that already contain eggs, and have been known to move eggs from neighbouring nests into their own. Some farmers use fake eggs made from plastic or stone to encourage hens to lay in a particular location. The result of this behavior is that a flock will use only a few preferred locations, rather than having a different nest for every bird.

Hens can also be extremely stubborn about always laying in the same location. It is not unknown for two (or more) hens to try to share the same nest at the same time. If the nest is small, or one of the hens is particularly determined, this may result in chickens trying to lay on top of each other.

Contrary to popular belief, roosters do not crow only at dawn, but may crow at any time of the day or night. Their crowing - a loud and sometimes shrill call - is a territorial signal to other roosters. However, crowing may also result from sudden disturbances within their surroundings.

Recent studies have shown that chickens (and possibly other bird species) still retain the genetic blueprints to produce teeth in the jaws, although these are dormant in living animals. These are a holdover from primitive birds such as Archaeopteryx, which were descended from theropod dinosaurs.