鸟类在迁移时所遵循的路线,无论是往南还是往北,无论是秋天还是春天,都极少经过城市。鸟群在田地开有垄沟的圆形山丘上,沿着森林边缘高高飞越天空,有时仿佛顺着一条河流的蜿蜒曲线或一条山谷的洼地,有时又像随着看不见的风向而翱翔。但 The routes followed by migrating birds, whether they are south or north, rarely pass through cities, whether they fall or spring. Flock of Birds Flies round the ditch on a circular hill in the field, flying high above the edge of the forest over the sky, sometimes as if by a meandering curve of a river or a depression in a valley, sometimes flying like an invisible wind . but