The most populous bird in the world is the Domesticated Chicken. Today there are more chickens than humans.  The modern chicken is descended from wild jungle fowl in the Indus river valley in southern Asia.  Mentions of domesticated chicken appear in China around 1,400 BC, in Babylon around 600 BC, and in Greece around 500 BC.  Chickens were raised by the Romans and were widely eaten in Europe during the Middle Ages.  Chicken reached unprecedented heights of popularity since World War II.  The war itself led to shortages of other types of meat, while post-war development of industrial poultry farming made chicken cheaper.  Chicken became more popular after researchers identified it as a relatively healthy alternative to red meat.