When Korea held the Olympics in 1988, people set one hundred pigeons free. After that, pigeons became a problem destroyed city environment. First, their excretion spoils the beauty of the city, especially, parks. It’s too much, so people can’t clean. Second, there are many pigeons which are infected with heavy metals. It can be infectious and fatal to people. Third, they infiltrate grain markets to get feed. They cause damage to grain dealers.