The coturnix quail has a long history of domestication reaching back to 11th and 12th century Japan. Originally kept as song birds, and later recognized by eastern medicine to have extremely nutrient dense eggs led to the selective breeding of quail for eggs. Sadly due to the events of World War II the remaining lines of quail bred for their singing abilities was lost, but the quail egg industry has rebuilt and flourished.
The remaining quail lines have been bred to be extremely productive in egg laying, while maintaining a very quiet disposition and small space requirements. Due to being selectively bred for these qualities it only takes 20 or so birds to keep an average family in eggs year-round, as each female can lay between 250-300 eggs per year, and these birds can be stocked comfortably at 3 per square foot. In fact coturnix quail have been domesticated for some long that it is very rare that a quail will go brooding and reproduce with out the aid of human intervention and an incubator.
Another benefit to raising quail is that they reach maturity in as little as 8 weeks and will be in full laying production by week 10. This allows for extremely fast ramping up of egg and meat production on demand. Also because the reproduction stage is controlled by you, you can determine when you want to increase production for eggs and meat. This fast life cycle also aids in the ability of the quail to adapt to many different situations through only few generations of selective breeding. I have personal friends that are raising them from Wyoming to Texas with only mild modifications to their housing.