你的迷惑来自于断句,正确的断句为:
Gone,be the birds,when they don't wanna sing.
下面还接有一句,看了更清楚了:
Gone,people,all awkward with their things,
Gone.
be在首句中实际是起祈使句的动词的作用.
如果是整句的话(不断句),应该是Gone are the birds when they don't wanna sing.
这是倒装句,正序为Birds are gone when they don't wanna sing.
直接用be的句型还是有的,如新概念里就出现一句:
Whether it be bird,fish or beast,the porpoise is intrigued with anything that is alive.
海豚对凡是活的东西都感兴趣,不管是鸟、是鱼,还是野兽.
这是虚拟语气用在由 “whether” 引导的让步状语从句中,从句谓语用原形动词.