小时经常看赵忠祥的动物世界，虽然不明白什么叫适者生存，长大以后才对这句话有所领悟，不管是动物还是人都需要物竞天择,适者生存，当你看到成千上万的野生动物万里迁徙的时候，你就会肃然起敬。

While seeing an animal in the wild can be fun, seeing thousands of them migrating is mesmerizing and awe-inspiring. These awesome wildlife photos will show you just how amazing of a sight a migration can be!Every year, birds, mammals, fish, reptiles and other animals around the world migrate for various reasons.

How they know when and where to go? Although seasons and temperatures seem to be the most important factor, the whole mechanism is not yet clearly understood. Migration yields things not usually seen - tree branches bending from the weight of butterflies, birds, flying from Alaska to New Zealand without stopping.Also animals don't always just travel across the map, either - some fish migrate to different depths!