A reader who acquired two Brahma bantams asked what to do after a predator took one of them. The remaining bird was lonely.
Chickens, like these Barred Rocks at Ryon Carey's farm in Kansas, are social birds. They live in flocks and are at something of a loss on their own. Solitary chickens often forge relationships with a cat or dog or other animal, to need their social needs.
Chickens are well known for their pecking order. It's an important part of a chicken's day, jockeying around to reinforce social position and occasionally experiencing a change.
Start with no fewer than three chickens. One is often lost to a predator or other incident. Then the remaining two will at least have each other, until you can get more.
Communities such as Madison, Wisconsin, http://www.madcitychickens.com/, limit backyard chicken to four hens. If you can legally do so, plan on a small flock of eight to ten, even if you do not plan to keep a rooster and breed them. Having a few more avoids sad situations such as a single hen.