Following the flow of wind means that they're always heading toward areas of low pressure, 随着风向迁徙意味着 它们总是飞向低压地区
the journey to the sea is not always smooth or uninterrupted. 流向大海的过程也并非都是平缓连续的
they can always descend to lower warmer altitudes 便会搬迁到温暖的低海拔地区