Chickens are highly social animals who thrive in flocks of up to 30 members. A single chicken will not thrive in a solitary existence. Like other social birds, chickens like to eat and forage, roost and dust-bathe together. Unlike most other birds, they will lay eggs in common nests and often raise chicks communally. If you can't keep more than one chicken, you should consider another pet.
The Natural Chicken
Left to their own devices, chickens roost in trees, forage for insects or plants they enjoy, bathe in soft soil, drink from streams, lay eggs almost daily and raise chicks one or two times each year -- all in company with other chickens. Chickens are intelligent animals with complex pecking orders that determine social standing within groups. All of these things chickens do serve to remind us that a lone chicken, even in the best of homes, is not natural. Similarly, a flock of chickens confined in battery cages is not natural either. The secret to happy, healthy chickens is having proper facilities for all the activities they do, and keeping enough chickens so they can do those things together -- naturally.
The Single Chicken
In addition to being lonely, a single chicken will be bored. As a highly social, thinking being, a chicken doesn't want to sit alone all day with nothing to do any more than you would, and keeping at least two gives them someone to talk to. If you must have only one chicken as a pet, get a hen. Hens are more docile, quieter and affectionate than roosters, and they adapt to being handled better. For her protection and socialization, keep your single chicken in the house just as you would a pet dog or cat so she can interact with her humans in lieu of a flock. You also need to provide her interesting things to do. Build a chicken tractor -- a rolling secure pen -- for her to spend some time outside scratching for worms and bugs each day. Hang an apple for her to peck at, buy a small ball for her to chase, or entertain her with other fun bird toys.
Chickens for Eggs
If you want chickens to supply fresh eggs for your family, you will certainly need at least three hens to get a dozen eggs per week. Each hen lays only one egg in a 25-hour period, so the average laying-hen will produce five or six eggs per week at her peak. During molting, heat or other stress or during low-light conditions in winter, egg production drops and many hens may temporarily stop laying altogether. Since egg-laying is a regular part of a healthy hen's life, you don't need a rooster to have fresh eggs. The eggs will simply not be fertile. But they will be edible.
Chickens need clean, fresh water and nutritious, quality food daily, served in dispensers that prevent hens from perching on them and from getting in their food or water and fouling it. Provide plenty of commercial pellets and scratch feed; supplement with fresh fruits and vegetables, and allow your chickens to forage for insects and wild plant material regularly. The main thing is to give your hens places to do the things chickens do. They need space to stretch their wings and wander around without crowding, which can lead to conflicts, and they need an outside area where they can scratch, dust-bathe or race around naturally. They need at least one comfortable, quiet nesting box per every three hens, and raised roosts for sleeping -- all inside a well-ventilated but secure house you can close against marauding foxes and racoons each night.