the movement of large numbers of people, birds or animals from one place to another 迁移；移居；迁徙
seasonal migration
季节性迁徙
mass migrations
大规模的迁移
the movement of large numbers of people, birds or animals from one place to another 迁移；移居；迁徙
seasonal migration
季节性迁徙
mass migrations
大规模的迁移