Cursorial Birds and Swimming Birds

　　In the long process of survival competition, different birds gradually adapt themselves to different habitat and develop into different ecological species. 

　　Birds living in campos and tropical deserts such as ostrich and emu have larger sizes. Their wings degenerate and they lost their ability to fly. But their feet are very strong and they can run very quickly. Therefore, they become cursorial birds.

　　Wild ducks, wild geese, pelicans, cormorants, gulls, albatrosses, frigate birds and sea swallows like to live on rivers, lakes and seawaters. Some of them are good at swimming and some are good at diving; therefore, they become birds of swimming. 

　　Egrets, water rails, cranes and storks have long necks, legs and bills. They like to walk and search food in shallow waters and swampland. Therefore, they are called wading birds.

　　All kinds of chickens, turtledoves and doves often walk on the ground. They are good at walking instead of flying. Thus, they are called terrestrial birds.