求翻译：“如果候鸟失去了南方，眼睛无法改变焦距，又会怎么样呢？”我自言自语，“我真的该走了，这夜该很美。”是什么意思？

"If birds lost the South, eyes can't change the focal length, but what about? "I said to himself," I really should go, this night was beautiful. ”