Beijing, March 14 (Youth.cn) - Photo taken in Beidagang Wetland in Tianjin on March 13th. Egrets fly freely. With the temperature goes up, migrant birds gradually begin to migrate. Peak migration season of migrant birds begins from March in Tianjin and will last until end May. It is estimated that more than 500,000 migrant birds will pass through this area in this spring. Photo/CFP