Chickens eat barley and when slaughtered produce chicken meat used for cooking. Eggs that hatch, or eggs crushed in the grain mortar of a kitchen, produce crushed eggshells used for Cut Stone Obelisks and for Alchemy. Eggs, hens, and roosters can also be fed to cobras.
The egg came before the chicken: The first chickens came from eggs found in trees. Any person who knows the avian selection skill has a small chance of finding an egg every time they harvest wood from a tree. At this point, it is far simpler to trade for eggs or chickens than to search trees for eggs.
A Chicken Coop requires the following to build:
Eggs placed in a chicken coop will hatch into hens and (very rarely) roosters. Hens prevent eggs from hatching; if there are hens in a coop, no eggs will hatch. Roosters counter this effect: For every rooster in a coop, up to one egg will hatch at a time.
Hens in a coop will lay eggs. All eggs are fertile, regardless of the presence or absence of roosters.
It is worth noting that roosters are completely unnecessary when raising chickens. It is much simpler to keep two coops (one containing hens which lay eggs, and one containing only eggs which hatch new chickens) than it is to keep one coop containing both hens and roosters. (Alternately, a single coop may alternate periods of laying and hatching.)
The temperature of the coop appears to have an effect on the rate at which eggs hatch, hens lay new eggs, and chickens eat barley. Temperature may be controlled by adjusting the slats on the coop. Rumor has it that a temperature of 120 may be good for hatching eggs, and one of 80 may be good for laying.
Unfed chickens will eventually starve. Chickens eat 1 barley per real hour, or 3 Egypt hours.
Roosters are more likely to show up in a pen containing only 1-2 eggs. (Actually this conserves eggs - and it seems as if per hatching there is a max of 1 rooster).
At approximately 6 a.m. Egypt time, some percentage of eggs will hatch, and some percentage of hens will lay eggs. It seems that the laying occurs just after the hatching.
(See also: Agriculture, Livestock)