Why are pigeons found only in the city?

Actually pigeons, sometimes called rock doves are fairly common in rural and agricultural areas. They are just not seen in the kind of numbers they are in large cities. There are probably two reasons they prefer large metropolitan areas.

The first reason is the availability of food in the large cities. City pigeons will eat anything and it makes sense that there is more food left on and around the streets of big cities than on the streets of smaller more rural towns.

Another reason is that rock doves typically live only in open areas and rarely in densely wooded places. The big cities offer sites similar to their natural rocky ledges– under bridges, the ledges of tall buildings, etc.

Source: Wikipedia and the New York Times Book of Science Questions and Answers.