Tree don't care what the little bird sings
Trees are incapable of thoughts or feelings, and therefore a symbol of the indifference of the world itself. The world doesn’t care how beautiful or clever human beings think they are; it will still let them die. The trees don’t care how beautifully a bird can sing.
Also, the “tree” possibly represents the human race, and the “little bird” represents a person. Cave is essentially stating that one person’s opinion won’t make a bit of difference, as it will be drowned out by millions of other voices.
This song may very well be about indigenous peoples preparing to attack invasive christian settlers.
The Chief (tree) has hardened his heart to the words/warnings of his Messenger (bird)
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